Circuits and methods for motion detection

FIELD OF THE INVENTION

0001This invention relates generally to integrated circuits and, more particularly, to integrated circuits for detecting a movement of a ferromagnetic object.

BACKGROUND

0002Magnetic field sensors (e.g., rotation detectors) for detecting ferromagnetic articles and/or magnetic articles are known. The magnetic field associated with the ferromagnetic article or magnetic article is detected by a magnetic field sensing element, such as a Hall element or a magnetoresistance element, which provides a signal (i.e., a magnetic field signal) proportional to a detected magnetic field. In some arrangements, the magnetic field signal is an electrical signal.

0003The magnetic field sensor processes the magnetic field signal to generate an output signal that changes state each time the magnetic field signal crosses thresholds, either near to peaks (positive and/or negative peaks) or near to some other level, for example, zero crossings of the magnetic field signal. Therefore, the output signal has an edge rate or period indicative of a movement speed (e.g., a rotation speed) of the ferromagnetic or magnetic object, for example, a gear or a ring magnet.

0004One application for a magnetic field sensor is to detect the approach and retreat of each tooth of a rotating ferromagnetic gear, either a hard magnetic gear or a soft ferromagnetic gear. In some particular arrangements, a ring magnet having magnetic regions (including permanent or hard magnetic material) with alternating polarity is coupled to the ferromagnetic gear or is used by itself. The magnetic field sensor is responsive to approach and retreat of the magnetic regions of the ring magnet. In other arrangements, a gear is disposed proximate to a stationary magnet and the magnetic field sensor is responsive to perturbations of a magnetic field as the gear rotates.

0005In one type of magnetic field sensor, sometimes referred to as a peak-to-peak percentage detector (or threshold detector), one or more threshold levels are equal to respective percentages of the peak-to-peak magnetic field signal. One such peak-to-peak percentage detector is described in U.S. Pat. No. 5,917,320 entitled “Detection of Passing Magnetic Articles While Periodically Adapting Detection Threshold” and assigned to the assignee of the present invention.

0006Another type of magnetic field sensor, sometimes referred to as a slope-activated detector (or peak referenced detector), is described in U.S. Pat. No. 6,091,239 entitled “Detection Of Passing Magnetic Articles With a Peak Referenced Threshold Detector,” also assigned to the assignee of the present invention. In the peak referenced magnetic field sensor, the threshold signal differs from the positive and negative peaks (i.e., the peaks and valleys) of the magnetic field signal by a predetermined amount. Thus, in this type of magnetic field sensor, the output signal changes state when the magnetic field signal comes away from a peak or valley of the magnetic field signal by the predetermined amount.

0007It should be understood that, because the above-described threshold detector and the above-described peak referenced detector both have circuitry that can identify the positive and negative peaks of a magnetic field signal, the threshold detector and the peak referenced detector both include a circuit portion, which is configured to detect positive peaks and/or negative peaks of the magnetic field signal. The threshold detector and the peak referenced detector, however, each use the detected peaks in different ways.

0008In order to accurately detect the positive and negative peaks of a magnetic field signal, the rotation detector is capable of tracking at least part of the magnetic field signal. To this end, typically, one or more digital-to-analog converters (DACs) can be used to generate a tracking signal, which tracks the magnetic field signal. For example, in the above-referenced U.S. Pat. Nos. 5,917,320 and 6,091,239, two DACs are used, one (PDAC) to detect the positive peaks of the magnetic field signal and the other (NDAC) to detect the negative peaks of the magnetic field signal.

0009Some types of rotation detectors perform one or more types of initialization or calibration, for example, at a time near to start up or power up of the rotation detector, or otherwise, from time to time as desired. During one type of calibration, the above-described threshold level is determined. In some types of calibration, a time interval during which the calibration occurs is determined in accordance with a predetermined number of cycles of the magnetic field signal. Thus, for fast magnetic field signals (e.g., for fast rotating gears), the time available for calibration is small. In those applications for which the movement or rotation is rapid and the time available for calibration is small, the rotation detector might not provide accurate motion detection fast enough.

0010It would, therefore, be desirable to provide a movement detector (e.g., a rotation detector) that can provide accurate and reliable motion detection (rotation speed and/or rotation direction) within a relatively short time frame, as well as over relatively long time frames.

SUMMARY

0011In general overview, the invention is directed to aspects of a circuit capable of detecting movement of an object within a relatively short period of time and, in some embodiments, detecting a speed and/or a direction of movement of an object within a relatively short period of time. The circuit detects object movement using one or more predetermined threshold detectors based on a predetermined threshold of a magnetic field signal associated with a magnetic field of an object. The circuit also detects object movement using one or more tracking threshold detectors by tracking the magnetic field signal over time. The predetermined threshold detectors can detect object movement quickly in comparison to the tracking threshold detectors, which require a calibration period (for example, a period which may include a period from startup or power up of a circuit) to track positive and negative peaks of the magnetic field signal. The circuit includes an output selector to generate an output related to the output of one of the predetermined threshold detectors or the tracking threshold detectors based on a predetermined condition. In some embodiments, the predetermined condition is related to a number of cycles of a magnetic field signal or the calibration time period of the tracking threshold detectors.

0012In some embodiments, a circuit capable of detecting a speed and a direction of a moving object includes a pair of predetermined threshold detectors responsive to a first pair of magnetic field elements (operative to provide a first magnetic field signal) and a second pair of magnetic field elements (operative to provide a second magnetic field signal). The first and second magnetic field signals are proportional to responses of the first and second pairs of magnetic field elements. The circuit also includes a pair of tracking threshold detectors responsive to the first and second magnetic field signals. The output selector generates an output signal related to a combination of output signals generated by the pair of predetermined threshold detectors and the pair of tracking threshold detectors based on the predetermined condition.

0013The circuit may be used in applications in which it is desired, needed, or necessary to detect object movement quickly and to generate an output signal indicative of such object movement. The object is not limited to any particular type of object which may include, but is not limited to, a toothed gear, crankshaft, camshaft, mechanical component of a toy or tool, etc. The object may include a ferromagnetic object, such as a soft ferromagnetic object. By way of non-limiting examples, the circuit may be used to detect movement of gears in a vehicle (for example, direction of rotation of transmission gears during vehicle operation), movement of vehicle wheels (for example, to generate an output signal indicative of forward or backward movement of a vehicle), etc.

0014In accordance with one aspect of the invention, a circuit responsive to movement of an object includes a magnetic field sensing element operative to provide a magnetic field signal proportional to a magnetic field associated with the object, a predetermined threshold detector including a comparator having a first input responsive to the magnetic field signal, a second input responsive to a predetermined threshold, and an output at which is provided a predetermined threshold detector output signal, and a tracking threshold detector including a tracking circuit coupled to receive the magnetic field signal and configured to track positive and negative peaks of the magnetic field signal and to generate a tracking signal, and a comparator having a first input responsive to the magnetic field signal, a second input responsive to an input signal related to the tracking signal, and an output at which is provided a tracking threshold detector output signal. The circuit also includes an output signal selector having a first input responsive to the tracking threshold detector output signal, a second input responsive to the predetermined threshold detector output signal, and configured to generate a circuit output signal related to at least one of the predetermined threshold detector output signal or the tracking threshold detector output signal based upon a predetermined condition.

0015In further embodiments, the circuit includes one or more of the following features: the predetermined condition is related to a predetermined number of cycles of the magnetic field signal; the predetermined condition is related to a predetermined number of cycles of the predetermined threshold detector output signal; the predetermined condition corresponds to a predetermined time; at least one of an automatic gain control coupled to the magnetic field sensing element and configured to process the magnetic field signal, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment coupled to the magnetic field sensing element and configured to process the magnetic field signal, wherein the predetermined condition corresponds to a condition of the automatic offset adjustment, and; the output signal selector is further configured to generate the circuit output signal related to the predetermined threshold detector output signal during a calibration time period of the tracking threshold detector and to generate the circuit output signal related to the tracking threshold detector output signal after the calibration time period wherein the predetermined condition corresponds to the end of the calibration time period.

0016In another embodiment, the circuit includes one or more of the following features: the magnetic field sensing element is a first pair of magnetic field sensing elements, the magnetic field signal is a first magnetic field signal, and the predetermined threshold detector is a first predetermined threshold detector responsive to the first magnetic field signal and operative to provide a first predetermined threshold detector output signal having a first predetermined threshold detector phase, the circuit further including a second pair of magnetic field sensing elements operative to provide a second magnetic field signal, and a second predetermined threshold detector including a comparator having a first input responsive to the second magnetic field signal, a second input responsive to the predetermined threshold, and an output at which is provided a second predetermined threshold detector output signal having a second predetermined threshold detector phase, wherein the signal selector further includes a third input responsive to the second predetermined threshold detector output signal and a difference between the first and second predetermined threshold detector phases is indicative of a movement direction of the object; the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals; the predetermined condition is related to a predetermined number of cycles of one of the first or second predetermined threshold detector output signals; the predetermined condition corresponds to a predetermined time, and; at least one of an automatic gain control coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic gain control.

0017In a further embodiment, the circuit includes one or more of the following features: the magnetic field sensing element is a first pair of magnetic field sensing elements and the magnetic field signal is a first magnetic field signal, and the tracking threshold detector is a first tracking threshold detector responsive to the first magnetic field signal and operative to provide a first tracking threshold detector output signal having a frequency indicative of movement speed of the object and a first tracking threshold detector phase, the circuit further including a second pair of magnetic field sensing elements operative to provide a second magnetic field signal, and a second tracking threshold detector including a tracking circuit coupled to receive the second magnetic field signal and configured to track positive and negative peaks of the second magnetic field signal and to generate a second tracking signal and a comparator having a first input responsive to the second magnetic field signal, a second input responsive to an input signal related to the second tracking signal, and an output at which is provided a second tracking threshold detector output signal having a second tracking threshold detector phase wherein the signal selector further includes a third input responsive to the second tracking threshold detector output signal and a difference between the first and second tracking threshold detector phases is indicative of a movement direction of the object; the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals; the predetermined condition is related to a predetermined number of cycles of one of the first or second tracking threshold detector output signals; the predetermined condition corresponds to a predetermined time; at least one of an automatic gain control coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic offset adjustment; the predetermined threshold detector is a first predetermined threshold detector responsive to the first magnetic field signal and the first predetermined threshold detector comparator is responsive to a first predetermined threshold and is operative to provide a first predetermined threshold detector output signal having a frequency indicative of movement speed of the object and a first predetermined threshold detector phase, the circuit further including a second predetermined threshold detector including a second comparator circuit having an input responsive to the second magnetic field signal and another input responsive to a second predetermined threshold and operative to provide a second predetermined threshold detector output signal having a second predetermined threshold detector phase wherein the signal selector further comprises a fourth input responsive to the second predetermined threshold detector output signal and a difference between the first and second predetermined threshold detector phases is indicative of a movement direction of the object; at least one of the first or second predetermined threshold detectors includes a Schmitt trigger; the output signal selector further includes a third input responsive to the second tracking threshold detector output signal and a fourth input responsive to the second predetermined threshold detector output signal and is further configured to provide the circuit output signal corresponding to a combination of the first and second tracking threshold detector output signals or a combination of the first and second predetermined threshold detector output signals based upon the predetermined condition.

0018In accordance with another aspect of the invention, a circuit responsive to movement of an object including a first pair of magnetic field sensing elements operative to provide a first magnetic field signal proportional to a magnetic field associated with the object, a second pair of magnetic field sensing elements operative to provide a second magnetic field signal proportional to the magnetic field, a first predetermined threshold detector including a first comparator circuit having an input responsive to the first magnetic field signal and another input responsive to a first predetermined threshold and an output at which is provided a first predetermined threshold detector output signal having a frequency indicative of movement speed of the object and a first predetermined threshold detector phase, a second predetermined threshold detector including a second comparator circuit having an input responsive to the second magnetic field signal and another input responsive to a second predetermined threshold and an output at which is provided a second predetermined threshold detector output signal having a second predetermined threshold detector phase, wherein a difference between the first and second predetermined threshold detector phases is indicative of a movement direction of the object, a first tracking threshold detector responsive to the first magnetic field signal and an output at which is provided a first tracking threshold detector output signal having a frequency indicative of a tracking threshold speed of the object and a first tracking threshold detector phase, a second tracking threshold detector responsive to the second magnetic field signal and an output at which is provided a second tracking threshold detector output signal having a second tracking threshold detector phase different than the first tracking threshold detector phase, wherein a difference between the first and second tracking threshold detector phases is indicative of the movement direction of the object. The circuit also includes an output signal selector coupled to receive the first predetermined threshold detector output signal, the second predetermined threshold detector output signal, the first tracking threshold detector output signal, and the second tracking threshold detector output signal and configured to generate a circuit output signal related to at least one of the received detector signals based upon a predetermined condition.

0019In a further embodiment, the circuit includes one or more of the following features: the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals; the predetermined condition is related to a predetermined number of cycles of one of the first predetermined threshold detector output signal, second predetermined threshold detector output signal, first tracking threshold detector output signal, or second tracking threshold detector output signal; the predetermined condition corresponds to a predetermined time, and; at least one of an automatic gain control coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment coupled to one of the first pair or the second pair of magnetic field sensing elements and configured to process a corresponding one of the first or second magnetic field signals, wherein the predetermined condition corresponds to a condition of the automatic offset adjustment.

0020In accordance with yet another aspect, a method of detecting a movement of an object includes generating a magnetic field signal proportional to a magnetic field associated with the object, generating a tracking signal responsive to the magnetic field signal to track positive and negative peaks of the magnetic field signal, generating a predetermined threshold output signal responsive to the magnetic field signal and to a predetermined threshold, generating a tracking threshold output signal responsive to the magnetic field signal and to the tracking signal, and providing an overall output signal related to a selected one of the predetermined threshold output signal or the tracking threshold output signal based upon a predetermined condition.

0021In another embodiment, the method includes one or more of the following features: the predetermined condition is related to a predetermined number of cycles of the magnetic field signal; the predetermined condition is related to a predetermined number of cycles of the predetermined threshold output signal; the predetermined condition corresponds to a predetermined time; processing the magnetic field signal using at least one of an automatic gain control, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic adjustment control, wherein the predetermined condition corresponds to a condition of the automatic adjustment control; said providing the overall output signal further includes selecting the overall output signal to be related to the predetermined threshold output signal during a calibration time period, and selecting the overall output signal to be related to the tracking threshold output signal after the calibration time period, wherein the predetermined condition corresponds to the end of the calibration time period; said magnetic field signal is a first magnetic field signal proportional to a magnetic field of the object at a first position, said tracking signal is a first tracking signal responsive to the first magnetic field signal, said tracking threshold output signal is a first tracking threshold output signal responsive to the first magnetic field signal and to the first tracking signal, wherein the first tracking threshold output signal has a frequency indicative of a movement speed of the object and a first tracking threshold output signal phase, and said predetermined threshold output signal is a first predetermined threshold output signal responsive to the first magnetic field signal and to a first predetermined threshold, the first predetermined threshold output signal having a frequency indicative of the movement speed of the object and having a first predetermined threshold output signal phase, further including generating a second magnetic field signal proportional to a second magnetic field associated with the object at a second position offset from the first position, generating a second tracking signal responsive to the second magnetic field signal to track positive and negative peaks of the second magnetic field signal, generating a second tracking threshold output signal responsive to the second magnetic field signal and to the second tracking signal and having a second tracking threshold output signal phase, a difference of the first and second tracking threshold output signal phases indicative of a movement direction of the object, and generating a second predetermined threshold output signal responsive to the second magnetic field signal and to a second predetermined threshold and having a second predetermined threshold output signal phase, a difference of the first and second output signal phases indicative of movement direction of the object, wherein said overall output signal is further related to a selected one of a combination of the first and second predetermined threshold output signals or a combination of the first and second tracking threshold output signals based upon the predetermined condition; the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals; the predetermined condition is related to a predetermined number of cycles of one of the first predetermined threshold detector output signal, second predetermined threshold detector output signal, first tracking threshold detector output signal, or second tracking threshold detector output signal; the predetermined condition corresponds to a predetermined time, and; further including processing one of the first or second magnetic field signals using at least one of an automatic gain control, wherein the predetermined condition corresponds to a condition of the automatic gain control, or an automatic offset adjustment, wherein the predetermined condition corresponds to a condition of the automatic offset adjustment.

BRIEF DESCRIPTION OF THE DRAWINGS

0022The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which:

0023<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram showing an exemplary circuit for object motion detection, having a predetermined threshold detector, a tracking threshold detector, and an output signal selector;

0024<figref idref="DRAWINGS">FIG. 2</figref> is a block diagram showing another exemplary circuit for object motion detection, having one or more predetermined threshold detectors, one or more tracking threshold detectors, and an output signal selector;

0025<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram showing an exemplary peak-to-peak percentage detector that can be used in the tracking threshold detector of <figref idref="DRAWINGS">FIG. 1</figref>;

0026<figref idref="DRAWINGS">FIG. 4A</figref> is a block diagram showing an exemplary peak referenced detector that can be used in the tracking threshold detector of <figref idref="DRAWINGS">FIG. 1</figref>;

0027<figref idref="DRAWINGS">FIG. 4B</figref> is a graph showing illustrative waveforms associated with the peak referenced detector of <figref idref="DRAWINGS">FIG. 4A</figref>;

0028<figref idref="DRAWINGS">FIG. 5</figref> is a block diagram showing an exemplary zero-crossing detector that can be used in the tracking threshold detector of <figref idref="DRAWINGS">FIG. 1</figref>;

0029<figref idref="DRAWINGS">FIG. 6</figref> is a flow chart representative of a method for object motion detection that may be implemented in the circuit of <figref idref="DRAWINGS">FIGS. 1 and 2</figref>;

0030<figref idref="DRAWINGS">FIG. 7</figref> is a graph showing magnetic field signals and predetermined threshold detector output signals associated with a circuit embodiment of <figref idref="DRAWINGS">FIG. 2</figref>;

0031<figref idref="DRAWINGS">FIG. 8</figref> is a graph showing magnetic field signals and tracking threshold detector output signals associated with a circuit embodiment of <figref idref="DRAWINGS">FIG. 2</figref>; and

0032<figref idref="DRAWINGS">FIG. 9</figref> is a graph showing output signal selection of an output signal selector that can be used with a circuit embodiment of <figref idref="DRAWINGS">FIG. 2</figref>.

DETAILED DESCRIPTION

0033Before describing the inventive systems, methods, and techniques, some introductory concepts and terminology are explained. As used herein, the term “magnetic field sensing element” is used to describe a variety of types of electronic elements that can sense a magnetic field. The magnetic field sensing elements can be, but are not limited to, Hall effect elements, magnetoresistance elements, or magnetotransistors. As is known, there are different types of Hall effect elements. These Hall effect elements may be made of a IV type semiconductor material such as Silicon (Si) or Germanium (Ge), or a III-V type semiconductor material such as Gallium-Arsenide (GaAs) or an Indium compound, for example, Indium-Antimonide (InSb).

0034As is also known, there are different types of magnetoresistance elements, for example, anisotropic magnetoresistance (AMR) elements, giant magnetoresistance (GMR) elements, tunneling magnetoresistance (TMR) elements, and magnetic tunnel junction (MTJ) elements.

0035Some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, most, but not all, types of magnetoresistance elements tend to have axes of maximum sensitivity parallel to the substrate and most, but not all, types of Hall elements tend to have axes of sensitivity perpendicular to a substrate.

0036As used herein, the term “magnetic field sensor” is used to describe a circuit that includes a magnetic field sensing element. Magnetic field sensors are used in a variety of applications including, but not limited to, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch or proximity detector that senses the proximity of a ferromagnetic or magnetic object, a motion detector (e.g., a rotation detector) that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet or teeth of a ferromagnetic gear, and a magnetic field sensor that senses a magnetic field density of a magnetic field. Rotation detectors are used as examples herein. However, the circuits and techniques described herein apply also to any magnetic field sensor capable of detecting a motion of an object.

0037Operation of a magnetic field sensor in a so-called “calibration mode,” also referred to herein as an “initialization mode,” is described herein. Reference is also made herein to operation of a magnetic field sensor in a so-called “running mode.” The calibration mode can occur at the beginning of operation (or from time to time as desired) and the running mode is achieved at other times. Operation of the running mode is described in greater detail in one or more of the above-mentioned patents, notably, U.S. Pat. No. 5,917,320 and U.S. Pat. No. 7,362,094, which are incorporated by reference herein in their entirety.

0038While a calibration time period is discussed herein, and end of which ends the calibration mode discussed herein in accordance with certain criteria, it should be recognized that other calibrations can be performed after the end of the indicated calibration time period. For example, an automatic gain control can continue calibrating after the end of the indicated calibration time period. At some point after the end of the indicated calibration time period, but not necessarily coincident with the end of the indicated calibration time period, the magnetic field sensors described herein can enter the running mode, during which updates to values of circuit parameters can update in a different way than during the calibration mode.

0039Referring to <figref idref="DRAWINGS">FIG. 1</figref>, an exemplary circuit <b>100</b> responsive to movement of an object <b>124</b> includes a magnetic field sensing element <b>104</b> for generating differential signal <b>104</b>A, <b>104</b>B (i.e., a magnetic field signal) proportional to a magnetic field associated with the object <b>124</b>. The magnetic field sensing element <b>104</b> can include, but is not limited to, a Hall effect element, a magnetoresistance element, or a magnetotransistor.

0040The object <b>124</b> can be an object configured to rotate, for example, a ferromagnetic gear. The circuit <b>100</b> can include an amplifier <b>106</b> coupled to receive the differential signal <b>104</b>A, <b>104</b>B from the magnetic field sensing element <b>104</b> and configured to generate a signal <b>106</b>A (also a magnetic field signal).

0041Circuit <b>100</b> also includes a predetermined threshold detector <b>120</b>. In some embodiments, the predetermined threshold detector <b>120</b> includes an amplifier <b>122</b> coupled to receive the signal <b>106</b>A and configured to generate a signal <b>122</b>A (also a magnetic field signal). In some embodiments, the amplifier <b>122</b> includes an automatic gain control (AGC) amplifier and/or the circuit <b>100</b> includes an automatic offset adjustment (AOA).

0042The predetermined threshold detector <b>120</b> can include a comparator <b>128</b> having a first input <b>128</b>A responsive to the magnetic field signal <b>122</b>A, a second input <b>128</b>B responsive to a predetermined threshold <b>130</b>, and an output <b>128</b>C at which is provided a predetermined threshold detector output signal <b>140</b>. In some embodiments, the predetermined threshold <b>130</b> is an electrical signal having a reference voltage value, for example 1.5 volts.

0043Circuit <b>100</b> also includes a tracking threshold detector <b>110</b>. In some embodiments, the tracking threshold detector <b>110</b> includes an amplifier <b>112</b> coupled to receive the signal <b>106</b>A and configured to generate a signal <b>112</b>A (also a magnetic field signal). In some embodiments, the amplifier <b>112</b> includes an AGC amplifier and/or the circuit <b>100</b> includes an AOA.

0044The tracking threshold detector <b>110</b> can include a tracking circuit <b>116</b> coupled to receive the signal <b>112</b>A and configured to track positive and negative peaks of the signal <b>112</b>A and to generate a tracking signal <b>117</b>. The tracking threshold detector <b>110</b> can also include comparator <b>118</b> having a first input <b>118</b>A responsive to signal <b>112</b>A, a second input <b>118</b>B responsive to an input signal related to the tracking signal <b>117</b>, and an output <b>118</b>C at which is provided a tracking threshold detector output signal <b>145</b>.

0045In further embodiments discussed in detail herein below, the tracking threshold detector <b>110</b> includes a peak-to-peak percentage detector (<figref idref="DRAWINGS">FIG. 3</figref>), a peak referenced detector (<figref idref="DRAWINGS">FIGS. 4A and 4B</figref>), a zero-crossing detector (<figref idref="DRAWINGS">FIG. 5</figref>), or combinations thereof.

0046In some embodiments, detectors <b>110</b>, <b>120</b> are rotation detectors to detect rotational movements of the object <b>124</b>, while in some other embodiments, detectors <b>110</b>, <b>120</b> are translation detectors to detect translational movements of the object <b>124</b>. It should be noted that detectors <b>110</b>, <b>120</b> are not limited to detection of stated kinds of object movement, and may detect other types of object movements, including combinations of object rotation and translation.

0047It should be noted that signals <b>104</b>A, <b>104</b>B, <b>106</b>A, <b>112</b>A, <b>122</b>A are all magnetic field signals, and are all indicative of a magnetic field experienced by the magnetic field sensing element <b>104</b>.

0048Circuit <b>100</b> can also include an output signal selector <b>150</b> having a first input <b>150</b>A responsive to the tracking threshold detector output signal <b>145</b>, a second input <b>150</b>B responsive to the predetermined threshold detector output signal <b>140</b>, and configured to generate a circuit output signal <b>155</b> related to at least one of the predetermined threshold detector output signal <b>140</b> or the tracking threshold detector output signal <b>145</b> based upon a predetermined condition.

0049As will be described more fully below in conjunction with <figref idref="DRAWINGS">FIGS. 8 and 9</figref>, in some embodiments, output signal selector <b>150</b> is configured to generate the circuit output signal <b>155</b> related to the predetermined threshold detector output signal <b>140</b> during a calibration time period of the tracking threshold detector <b>110</b> and to generate the circuit output signal <b>155</b> related to the tracking threshold detector output signal <b>145</b> after the calibration time period wherein the predetermined condition corresponds to the end of the calibration time period.

0050In some embodiments, the predetermined condition is related to a predetermined number of cycles of the magnetic field signal <b>106</b>A, for example, three cycles.

0051In other embodiments, the predetermined condition is related to a predetermined number of cycles of the predetermined threshold detector output signal <b>140</b>, for example, three cycles.

0052In still other embodiments, the predetermined condition corresponds to a predetermined time, for example, 1.0 second. In some embodiments, the predetermined time is related to the rotation speed and/or a predetermined time after rotation is detected. For faster rotation speeds, the time can be shorter while for slower rotation speeds the time can be longer.

0053In other embodiments, the circuit <b>100</b> includes at least one of an AGC or an AOA coupled to the magnetic field sensing element <b>104</b> and configured to process the signal (as may be similar to signal <b>106</b>A). In these embodiments, the predetermined condition corresponds to a condition of the AGC, for example, a gain of the AGC that has not changed for 3 cycles of the signal or a condition of the AOA, for example, an offset value of the AOA.

0054The predetermined condition should not be construed as limited to the above described conditions but can also be based on various algorithms to determine when tracking threshold detector <b>110</b> is calibrated and to determine proper rotation speed and/or direction information.

0055In some arrangements, the magnetic field sensing element <b>104</b> can be responsive to motion of the object <b>124</b>, for example, motion of ferromagnetic gear teeth upon a gear, of which gear teeth <b>124</b>A-<b>124</b>C upon the gear <b>124</b> are representative. To this end, a fixed magnet (not shown) can be disposed proximate to the magnetic field sensing element <b>104</b> and the gear teeth can disturb the magnetic field generated by the magnet as the gear rotates. However, in other arrangements, the magnetic field sensing element <b>104</b> can be responsive to movement of magnetic regions upon a magnet, for example, magnetic regions <b>126</b>A-<b>126</b>C upon a ring magnet <b>126</b>. In some particular arrangements, the ring magnet <b>126</b> and the gear <b>124</b> are coupled together with a shaft or the like. In these particular arrangements, the ring magnet <b>126</b> can be proximate to the magnetic field sensing element <b>104</b>.

0056The magnetic field sensing element <b>104</b> is responsive to proximity of the ring magnet <b>126</b> and, in particular, to proximity of passing magnetic regions north (N) and south (S) <b>126</b>A-<b>126</b>C. In operation, the magnetic field sensing element <b>104</b> produces the differential magnetic field signal <b>104</b>A, <b>104</b>B (and also the magnetic field signals <b>106</b>A, <b>112</b>A, <b>122</b>A) having a generally repeating pattern when the ring magnet <b>126</b> rotates, wherein each peak (positive and negative) of the pattern is associated with one of the magnetic regions N, S.

0057Referring now to <figref idref="DRAWINGS">FIG. 2</figref>, in a further embodiment, a circuit <b>200</b> includes a first predetermined threshold detector <b>220</b>A, a second predetermined threshold detector <b>220</b>B, and a tracking threshold detector <b>210</b>A. The circuit <b>200</b> can also include a first pair of magnetic field sensing elements <b>205</b>A, including magnetic field sensing element <b>204</b>A and magnetic field sensing element <b>204</b>C, operative to provide a differential magnetic field signal <b>274</b>A, <b>274</b>B, <b>294</b>A, <b>294</b>B proportional to a magnetic field associated with an object <b>224</b>. In some embodiments, the circuit <b>200</b> can include an amplifier <b>206</b>A coupled to receive a differential signal <b>274</b>A, <b>274</b>B from the first pair of magnetic field sensing elements <b>205</b>A and configured to generate a signal <b>276</b>A (also a magnetic field signal).

0058In some embodiments, the first predetermined threshold detector <b>220</b>A can include an amplifier <b>222</b>A coupled to receive the signal <b>276</b>A and configured to generate a signal <b>272</b>B (also a magnetic field signal). In some embodiments, the amplifier <b>222</b>A includes an AGC amplifier and/or the circuit <b>100</b> includes an AOA.

0059The first predetermined threshold detector <b>220</b>A can include a comparator <b>228</b>A having a first input <b>278</b>A responsive to the magnetic field signal <b>272</b>B, a second input <b>278</b>B responsive to a predetermined threshold <b>230</b>A, and an output <b>278</b>C at which is provided a first predetermined threshold detector output signal <b>240</b>A. The predetermined threshold <b>230</b>A may include a plurality of predetermined thresholds, for example, a first predetermined threshold and a second predetermined threshold.

0060The circuit <b>200</b> can also include a second pair of magnetic field sensing elements <b>205</b>B, including magnetic field sensing element <b>204</b>B and magnetic field sensing element <b>204</b>C, operative to provide a second differential magnetic field signal <b>284</b>A, <b>284</b>B, <b>294</b>A, <b>294</b>B proportional to the magnetic field associated with object <b>224</b>. In some embodiments, circuit <b>200</b> can include an amplifier <b>206</b>B coupled to receive the differential signal <b>284</b>A, <b>284</b>B, <b>294</b>A, <b>294</b>B from the second pair of magnetic field sensing elements <b>205</b>B and configured to generate a signal <b>286</b>A (also a magnetic field signal).

0061In further embodiments, the second predetermined threshold detector <b>220</b>B includes an amplifier <b>222</b>B coupled to receive the signal <b>286</b>A and configured to generate a signal <b>282</b>B (also a magnetic field signal). In still further embodiments, the amplifier <b>222</b>B includes an AGC amplifier and/or the circuit <b>100</b> includes an AOA.

0062The second predetermined threshold detector <b>220</b>B can also include a comparator <b>228</b>B having a first input <b>288</b>A responsive to the magnetic field signal <b>282</b>B, a second input <b>288</b>B responsive to a predetermined threshold <b>230</b>B, and an output <b>288</b>C at which is provided a second predetermined threshold detector output signal <b>240</b>B. In some embodiments, the predetermined threshold <b>230</b>B of detector <b>220</b>B is the same as the predetermined threshold <b>230</b>A of detector <b>220</b>A, while in some other embodiments, the predetermined thresholds <b>230</b>A, <b>230</b>B are different.

0063In some embodiments, the tracking threshold detector <b>210</b>A of circuit <b>200</b> includes an amplifier <b>212</b>A coupled to receive the signal <b>276</b>A and configured to generate a signal <b>272</b>A (also a magnetic field signal). In some embodiments, the amplifier <b>212</b>A includes an AGC amplifier and/or the circuit <b>100</b> includes an AOA.

0064The tracking threshold detector <b>210</b>A can include a tracking circuit <b>216</b>A coupled to receive the signal <b>272</b>A and configured to track positive and negative peaks of the signal <b>272</b>A and to generate a tracking signal <b>277</b>A. The tracking threshold detector <b>210</b>A can also include a comparator <b>218</b>A having a first input <b>278</b>A responsive to signal <b>272</b>A, a second input <b>278</b>B responsive to an input signal related to the tracking signal <b>277</b>A, and an output <b>278</b>C at which is provided a first tracking threshold detector output signal <b>245</b>A.

0065The circuit <b>200</b> can also include an output signal selector <b>250</b> (as may be similar to output signal selector <b>150</b> described in conjunction with <figref idref="DRAWINGS">FIG. 1</figref>) having a first input <b>250</b>A responsive to the tracking threshold detector output signal <b>245</b>A, a second input <b>250</b>B responsive to the first predetermined threshold detector output signal <b>240</b>A, and a third input <b>250</b>C responsive to the second predetermined threshold detector output signal <b>240</b>B. The output signal selector <b>250</b> is configured to generate a circuit output signal <b>255</b> related to at least one of the first predetermined threshold detector output signal <b>240</b>A, the tracking threshold detector output signal <b>245</b>A, or the second predetermined threshold detector output signal <b>240</b>B based upon a predetermined condition.

0066Output signal selector <b>250</b> selects signals <b>245</b>A, <b>245</b>B, <b>240</b>A, <b>240</b>B based on a predetermined condition and includes logic for example to determine speed and/or direction and/or vibration information based on one or more of these signals. For example, higher signal edge rates can correspond to relatively fast object movement and lower signal edge rates can correspond to relatively slow object movement. In embodiments in which the object is a rotating gear, for example, signal frequency (related to edge rate) is indicative of rotation speed of the gear. The relative phase sequences of rising and falling edges of two of the signals can be used to determine a direction of object movement. It will be understood that logic to determine speed and/or direction information may include analog logic, digital logic, and/or mixed logic.

0067In these embodiments, the first predetermined threshold detector output signal <b>240</b>A has a first predetermined threshold detector phase and the second predetermined threshold detector output signal <b>240</b>B has a second predetermined threshold detector phase. A difference between the first and second predetermined threshold detector phases is indicative of a movement direction of the object <b>224</b>. A frequency of either the predetermined threshold detector output signal <b>240</b>A, the threshold detector output signal <b>245</b>A, or the second predetermined threshold detector output signal <b>240</b>B is related to a speed of rotation of the object <b>224</b>.

0068In a further embodiment, the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals <b>276</b>A, <b>286</b>A, for example, three cycles.

0069In another embodiment, the predetermined condition is related to a predetermined number of cycles of one of the first or second predetermined threshold detector output signals <b>240</b>A, <b>240</b>B, for example, three cycles.

0070In a further embodiment, the predetermined condition corresponds to a predetermined time. In some embodiments, the predetermined time is related to the rotation speed and/or a predetermined time after rotation is detected.

0071In another embodiment, circuit <b>200</b> includes an AGC coupled to one of the first or second pair of magnetic field sensing elements <b>205</b>A, <b>205</b>B and configured to process a respective one of the first or second magnetic field signals (<b>276</b>A, <b>286</b>A) wherein the predetermined condition corresponds to a condition of the AGC, for example, a gain of the AGC. Circuit <b>200</b> optionally includes an AOA coupled to one of the first or second pair of magnetic field sensing elements <b>205</b>A, <b>205</b>B and configured to process a respective one of the first or second magnetic field signals (<b>276</b>A, <b>286</b>A) wherein the predetermined condition corresponds to a condition of AOA.

0072Referring again to <figref idref="DRAWINGS">FIG. 2</figref>, in another embodiment, the circuit <b>200</b> includes the first tracking threshold detector <b>210</b>A, a second tracking threshold detector <b>210</b>B, and the first predetermined threshold detector <b>220</b>A. In this embodiment, circuit <b>200</b> includes the first pair of magnetic field sensing elements <b>205</b>A and the second pair of magnetic field sensing elements <b>205</b>B.

0073In some embodiments, the second tracking threshold detector <b>210</b>B includes an amplifier <b>212</b>B coupled to receive the signal <b>286</b>A (from the second magnetic field sensing element <b>205</b>B) and configured to generate a signal <b>282</b>A (also a magnetic field signal). In some embodiments, the amplifier <b>212</b>B is an AGC amplifier and/or the circuit <b>100</b> includes an AOA.

0074The second tracking threshold detector <b>210</b>B can include a tracking circuit <b>216</b>B coupled to receive the signal <b>282</b>A and configured to track positive and negative peaks of the signal <b>282</b>A and to generate a tracking signal <b>277</b>B. The second tracking threshold detector <b>210</b>B can also include a comparator <b>218</b>B having a first input <b>288</b>A responsive to signal <b>282</b>A, a second input <b>288</b>B responsive to an input signal related to the tracking signal <b>277</b>B, and an output <b>288</b>C at which is provided a second tracking threshold detector output signal <b>245</b>B.

0075In this embodiment, the circuit <b>200</b> includes the output signal selector <b>250</b> (as may be similar to output signal selector <b>150</b> described in conjunction with <figref idref="DRAWINGS">FIG. 1</figref>) having a first input <b>250</b>A responsive to the first tracking threshold detector output signal <b>245</b>A, a second input <b>250</b>D responsive to the second tracking threshold detector output signal <b>245</b>B, and a third input <b>250</b>B responsive to the first predetermined threshold detector output signal <b>240</b>A. The output signal selector <b>250</b> is configured to generate a circuit output signal <b>255</b> related to at least one of the first tracking threshold detector output signal <b>245</b>A, the first predetermined threshold detector output signal <b>240</b>A, or the second tracking threshold detector output signal <b>245</b>B based upon a predetermined condition.

0076In this embodiment, the first tracking threshold detector output signal <b>245</b>A has a first tracking threshold detector phase and the second tracking threshold detector output signal <b>245</b>B has a second tracking threshold detector phase. A difference between the first and second tracking threshold detector phases is indicative of a movement direction of the object <b>224</b>. A frequency of either the first tracking threshold detector output signal <b>245</b>A, the first predetermined threshold detector output signal <b>240</b>A, or the second tracking threshold detector output signal <b>245</b>B is related to a speed of rotation of the object <b>224</b>.

0077Referring yet again to <figref idref="DRAWINGS">FIG. 2</figref>, in a further embodiment, a circuit <b>200</b> includes the first tracking threshold detector <b>210</b>A, the second tracking threshold detector <b>210</b>B, the first predetermined threshold detector <b>220</b>A, and the second predetermined threshold detector <b>220</b>B. In this embodiment, the output signal selector <b>250</b> includes a first input <b>250</b>A responsive to the first tracking threshold detector output signal <b>245</b>A, a second input <b>250</b>B responsive to the first predetermined threshold detector output signal <b>240</b>A, a third input <b>250</b>C responsive the second predetermined threshold detector output signal <b>240</b>B, and a fourth input <b>250</b>D responsive the second tracking threshold detector output signal <b>245</b>B. In such an arrangement, the output signal selector <b>250</b> is configured to provide the circuit output signal <b>255</b> corresponding to a combination of the first and second tracking threshold detector output signals <b>245</b>A, <b>245</b>B or a combination of the first and second predetermined threshold detector output signals <b>240</b>A, <b>240</b>B based upon the predetermined condition.

0078In a further embodiment, the predetermined condition is related to a predetermined number of cycles of one of the first or second magnetic field signals <b>276</b>A, <b>286</b>A, for example, three cycles.

0079In a further embodiment, the predetermined condition is related to a predetermined number of cycles of one of the first predetermined threshold detector output signal <b>240</b>A, the second predetermined threshold detector output signal <b>240</b>B, the first tracking threshold detector output signal <b>245</b>A, or the second tracking threshold detector output signal <b>245</b>B, for example, three cycles.

0080In a further embodiment, at least one of the first or second predetermined threshold detectors <b>220</b>A, <b>220</b>B includes a Schmitt trigger.

0081It should be apparent to one of ordinary skill in the art that the circuit is not limited to above-described configurations, and may encompass other desired configurations including multiple tracking threshold detectors (i.e., more than two tracking threshold detectors) and/or multiple predetermined threshold detectors (i.e., more than two predetermined threshold detectors).

0082Operation of the circuits <b>100</b>, <b>200</b> is described below in conjunction with <figref idref="DRAWINGS">FIG. 7-9</figref>.

0083Referring now to <figref idref="DRAWINGS">FIG. 3</figref>, a peak-to-peak percentage detector <b>26</b> suitable for use as the tracking circuit <b>116</b> of <figref idref="DRAWINGS">FIG. 1</figref> is shown. Peak-to-peak percentage detector <b>26</b> is coupled to a comparator <b>428</b>, like comparator <b>118</b> of <figref idref="DRAWINGS">FIG. 1</figref>. A magnetic field signal <b>18</b>, like signal <b>112</b>A of <figref idref="DRAWINGS">FIG. 1</figref>, is provided as an input to the detector <b>26</b>.

0084Magnetic field signal <b>18</b> is applied to a non-inverting input of a first comparator <b>400</b> and to the inverting input of a second comparator <b>404</b>. The output signals of comparators <b>400</b> and <b>404</b> provide input signals GT_PDAC <b>458</b> and LT_NDAC <b>461</b>, respectively, to an update controller <b>409</b> that provides control signals to counters <b>414</b> and <b>430</b>, as shown.

0085The update controller <b>409</b> provides a p_updn signal <b>463</b> to an UPDN (up/down) input of a counter <b>414</b> to control the count direction. As will become apparent, the p_updn signal <b>463</b> normally causes the counter <b>414</b> to count up. Under certain conditions however, the p_updn signal <b>463</b> causes the counter <b>414</b> to count down for some clock cycles. The counter <b>414</b> is clocked by a system clock signal, CLK. A p_hold signal <b>465</b> is coupled to a HOLD input of the counter <b>414</b>. The counter output is held constant (i.e., the counter is disabled) when the HOLD input signal is at a first logic level and is released (i.e., the counter is enabled) when HOLD input signal is at a second logic level. The counter <b>414</b> may be a six bit counter which is enabled when the HOLD input is low.

0086The outputs of the counter <b>414</b> are coupled to inputs of a positive digital-to-analog converter (PDAC) <b>403</b>. The PDAC <b>403</b> is buffered by a buffer <b>424</b> to provide a PDAC signal <b>402</b>, which may be a voltage that tracks positive peaks of the magnetic field signal <b>18</b> (i.e., a tracking signal).

0087The comparator <b>400</b>, counter <b>414</b>. PDAC <b>403</b>, and buffer <b>424</b> comprise a “positive portion” of the detector circuitry. A “negative portion” of the detector <b>26</b> is similarly arranged, as shown. In particular, update controller <b>409</b> provides an n_updn signal <b>466</b> to an UPDN input of counter <b>430</b> to control the count direction. As will become apparent, the n_updn signal <b>466</b> normally causes the counter <b>430</b> to count down. Under certain conditions however, the n_updn signal <b>466</b> causes the counter <b>430</b> to count up for some clock cycles. The counter <b>430</b> is clocked by a system clock signal, CLK. An n_hold signal <b>468</b> is coupled to a HOLD input of the counter <b>430</b>. The counter output is held constant (i.e., the counter is disabled) when the HOLD input signal is at a first logic level and is released (i.e., the counter is enabled) when the HOLD input signal is at a second logic level. The counter <b>430</b> may be a six bit counter which is enabled when the HOLD input is low.

0088The outputs of the counter <b>430</b> are coupled to inputs of a negative digital-to-analog converter (NDAC) <b>405</b>. The NDAC <b>405</b> is buffered by a buffer <b>436</b> to provide an NDAC signal <b>406</b>, which may be a voltage that tracks negative peaks of the magnetic field signal <b>18</b> (i.e., a tracking signal).

0089The buffered PDAC and NDAC signals <b>402</b>, <b>406</b> are coupled to a resistor divider comprising series-coupled resistors <b>408</b>, <b>412</b>, and <b>416</b> in order to generate peak-to-peak threshold signals THRESHHI and THRESHLO, as will be described more fully below in conjunction with <figref idref="DRAWINGS">FIG. 8</figref>.

0090Each of the threshold signals THRESHHI and THRESHLO is a percentage of the difference between the PDAC and NDAC voltages, or, in other words, a percentage of the peak-to-peak magnetic field signal <b>18</b>. As described more fully below in conjunction with <figref idref="DRAWINGS">FIG. 8</figref>, in one embodiment, an upper threshold value <b>440</b> is at approximately 75% of the peak-to-peak signal and a lower threshold value <b>444</b> is at approximately 25% of the peak-to-peak signal. It will be appreciated that other percentages may be suitable. Switches <b>424</b><i>a </i>and <b>424</b><i>b </i>are arranged and controlled so as to apply one of the threshold levels to comparator <b>428</b>, as shown. Switch <b>424</b><i>b </i>is controlled by the POSCOMP signal. In particular, switch <b>424</b><i>a </i>is controlled by an inverted version of the POSCOMP signal, or POSCOMPN. Further, the magnetic field signal <b>18</b> is applied to a non-inverting input of comparator <b>428</b>.

0091Referring now to <figref idref="DRAWINGS">FIG. 4A</figref>, a peak referenced detector <b>10</b> suitable for use as the tracking threshold detector <b>110</b> of <figref idref="DRAWINGS">FIG. 1</figref> is shown, which uses a single digital-to-analog converter (DAC) <b>28</b> to track a magnetic field signal <b>2</b>. The magnetic field signal <b>2</b> is coupled to an inverting input of a tracking comparator <b>20</b> which receives at a non-inverting input an output signal PEAKDAC (i.e., the tracking signal) of a DAC <b>28</b>, as shown. The magnetic field signal <b>2</b> is further coupled to an inverting input of a comparator <b>40</b>, like comparator <b>118</b> of <figref idref="DRAWINGS">FIG. 1</figref>, which receives at the non-inverting input the PEAKDAC signal and which generates a detector output signal, POSCOMP. The comparator <b>40</b> has internal hysteresis, here on the order of 100 mV, so that the POSCOMP output signal changes state when the magnetic field signal <b>2</b> exceeds the PEAKDAC signal by approximately 100 mV. The output signal of the comparator <b>20</b>, COMPOUT, is coupled to an exclusive OR (XOR) gate <b>36</b> which additionally receives the POSCOMP signal and which provides a HOLD input signal to an up/down counter <b>24</b>. Counter <b>24</b> is further responsive to a clock signal, CLK, and to the POSCOMP signal for controlling whether counter <b>24</b> counts up or down. The output of the counter <b>24</b> is converted into the tracking PEAKDAC signal by the DAC <b>28</b>.

0092As illustrated in <figref idref="DRAWINGS">FIG. 4B</figref>, whenever the magnetic field signal <b>2</b> exceeds the PEAKDAC signal by the small hysteresis level of comparator <b>20</b>, the COMPOUT signal transitions to a logic high level. The HOLD input to the counter <b>24</b> is coupled to the exclusive OR (XOR) gate <b>36</b>, which is coupled to COMPOUT and additionally receives the POSCOMP signal. Once the counter <b>24</b> counts up one step, the COMPOUT signal goes low causing the count value to be held until the signal exceeds the PEAKDAC signal by the small hysteresis level of comparator <b>20</b> again. When the signal reaches a positive peak, as occurs at time t₁, the PEAKDAC signal stays above the signal <b>2</b>, thereby causing the HOLD input to the counter <b>24</b> to be asserted until the hysteresis of the comparator <b>40</b> has been overcome, as occurs when the POSCOMP signal goes low, just before time t₂. In this way, the positive and negative peaks of the signal are tracked by the PEAKDAC signal and the detector output signal POSCOMP transitions when the signal differs from the PEAKDAC signal by more than the hysteresis amount of comparator <b>40</b> (as occurs at times t₀and t₂).

0093Referring now to <figref idref="DRAWINGS">FIG. 5</figref>, a so-called “zero-crossing detector” <b>500</b>, a tracking and comparator circuit, can be compared with the tracking circuit <b>116</b> and comparator <b>118</b> of <figref idref="DRAWINGS">FIG. 1</figref>. Here, an amplifier <b>506</b> is coupled to receive signals <b>502</b>A, <b>502</b>B, <b>504</b>A, <b>504</b>B from two magnetic field sensing elements <b>502</b>, <b>504</b>. The amplifier <b>506</b> is configured to generate a differential magnetic field signal <b>506</b>A, <b>506</b>B coupled to a band pass filter (BPF) <b>508</b>. The magnetic field signal <b>506</b>A, <b>506</b>B is comparable to the magnetic field signal <b>106</b>A of <figref idref="DRAWINGS">FIG. 1</figref>. The BPF <b>508</b> is configured to generate a differential filtered signal <b>508</b>A, <b>508</b>B. A comparator <b>528</b> is coupled to receive the differential filtered signal <b>508</b>A, <b>508</b>B and configured to generate a motion signal, POSCOMP <b>510</b>A.

0094Referring now to <figref idref="DRAWINGS">FIG. 6</figref>, a method <b>600</b> of detecting a movement of an object includes, at <b>602</b> generating a magnetic field signal proportional to a magnetic field associated with the object, at <b>604</b>, generating a tracking signal responsive to the magnetic field signal to track positive and negative peaks of the magnetic field signal, at <b>606</b>, generating a predetermined threshold output signal responsive to the magnetic field signal and to a predetermined threshold, at <b>608</b>, generating a tracking threshold output signal responsive to the magnetic field signal and to the tracking signal and, at <b>610</b>, providing an overall output signal related to a selected one of the predetermined threshold output signal or the tracking threshold output signal based upon a predetermined condition.

0095It should be appreciated that method <b>600</b> could be implemented in a circuit, for example, circuit <b>100</b> described in conjunction with <figref idref="DRAWINGS">FIG. 1</figref>, or circuit <b>200</b> described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>. Furthermore, one or more of the method steps (i.e., steps <b>602</b>, <b>604</b>, <b>606</b>, <b>608</b>, <b>610</b>) may be implemented in a processor and, in particular, may be implemented as computer software instructions loaded from a memory into a processor for execution.

0096Alternatively, one or more of the method steps may be performed by functionally equivalent circuits such as a digital signal processor circuit or an application specific integrated circuit (ASIC). The method does not depict the syntax of any particular programming language. Rather, the method illustrates the information one of ordinary skill in the art requires to fabricate circuits or to generate computer software to perform the processing required to implement at least a portion of the techniques described herein. It will be appreciated by those of ordinary skill in the art that the particular sequence of steps described is illustrative only and can be varied without departing from the spirit of the techniques described herein.

0097In a further embodiment of method <b>600</b>, the predetermined condition is related to a predetermined number of cycles of the magnetic field signal. In a non-limiting example, a processor may process the magnetic field signal to recognize a predetermined number of cycles of the magnetic field signal (for example, three cycles of the magnetic field signal). The processor determines that the predetermined condition has been met (i.e., that three cycles of the magnetic field signal have occurred) and provides an overall output signal by selecting one of the predetermined threshold output signal or the tracking threshold output signal. In one configuration, the processor provides an overall output signal related to the predetermined threshold output signal before the predetermined condition is realized (i.e., before the processor recognizes the predetermined number of cycles of the magnetic field signal), and provides the overall output signal related to the tracking threshold output signal after the predetermined condition is realized (i.e., after the processor recognizes the predetermined number of cycles of the magnetic field signal).

0098In another embodiment of the method <b>600</b>, the predetermined condition is related to a predetermined number of cycles of the predetermined threshold output signal. In a non-limiting example, a processor may process the predetermined threshold output signal to recognize a predetermined number of cycles of the signal (for example, three cycles of the predetermined threshold output signal). The processor determines that the predetermined condition has been met (i.e., that three cycles of the predetermined threshold output signal have occurred) and provides an overall output signal by selecting one of the predetermined threshold output signal or the tracking threshold output signal. In one configuration, the processor provides an overall output signal related to the predetermined threshold output signal before the predetermined condition is realized (i.e., before the processor recognizes three cycles of the predetermined threshold output signal), and provides the overall output signal related to the tracking threshold output signal after the predetermined condition is realized (i.e., after the processor recognizes the three cycles of the predetermined threshold output signal).

0099In a further embodiment of the method <b>600</b>, the predetermined condition corresponds to a predetermined time. The predetermined time may optionally be related to a calibration time of a circuit, such as circuit <b>100</b> described in conjunction with <figref idref="DRAWINGS">FIG. 1</figref> or circuit <b>200</b> described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>. As will be described more fully below, the calibration time may correspond to a calibration period related to offset and gain adjustments of the differential signals.

0100Accordingly, in a further embodiment, the method <b>600</b> includes selecting the overall output signal to be related to the predetermined threshold output signal during a calibration time period and selecting the overall output signal to be related to the tracking threshold output signal after the calibration time period. In this way, the predetermined condition corresponds to the end of the calibration time period.

0101In a non-limiting example, a processor provides a selected one of the predetermined threshold output signal or the tracking threshold output signal based upon the predetermined time (for example, in some embodiments, the time is related to target rotation speed). In a further embodiment, the predetermined time is defined relative to a time at which an object whose movement is to be detected begins to move or a time at which a circuit (as may be the same or similar to circuit <b>200</b>) starts up or powers up. In a non-limiting example, the object is a rotating gear coupled to a rotating shaft of an engine. The rotating gear can be used to detect motion (and, more particularly, the speed and direction of motion) of engine components. By way of a non-limiting example, for a vehicle, this may include motion detection of a crankshaft, exhaust camshaft, intake camshaft, piston, connecting rods, valves, transmission gears, wheels, etc.

0102It should be noted that the predetermined time may be defined relative to various timing events. For example, the above-mentioned engine may be placed in a neutral state during which engine components are at rest (or at idle) and no movement detection is desired or necessary. However, once the engine is engaged and components begin to operate, the processor tracks the elapsed time and provides the predetermined threshold output signal until reaching the predetermined time, after which, the processor provides the tracking threshold output signal.

0103In another embodiment, the method <b>600</b> includes processing the magnetic field signal using an AGC, wherein the predetermined condition corresponds to a condition of the AGC, for example, at a time when the AGC stops updating. In still further embodiments, the method <b>600</b> includes processing the magnetic field signal using an AOA, wherein the predetermined condition corresponds to a condition of the AOA, for example, an offset value.

0104Referring now to <figref idref="DRAWINGS">FIG. 7</figref>, a graph <b>700</b> has a horizontal axis with a scale in arbitrary units of time and a vertical axis in arbitrary units of voltage. One portion <b>700</b>A of the graph <b>700</b> includes a time-varying magnetic field signal <b>772</b>A representative of, for example, the magnetic field signal <b>272</b>B of <figref idref="DRAWINGS">FIG. 2</figref>. The magnetic field signal <b>772</b>A is responsive to a magnetic field associated with the movement of an object, as may be similar to object <b>224</b> described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>.

0105Another portion <b>700</b>C of the graph <b>700</b> includes a predetermined threshold detector output signal <b>740</b>A representative of, for example, the predetermined threshold detector output signal <b>240</b>A output from predetermined threshold detector <b>220</b>A of <figref idref="DRAWINGS">FIG. 2</figref>. In operation, the predetermined threshold detector output signal <b>740</b>A is representative of the output of a comparator (as may be similar to comparator <b>228</b>A described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>) coupled at a first input to the magnetic field signal <b>772</b>A and at a second input to a reference voltage representative of a predetermined threshold Th. The magnetic field signal <b>772</b>A crosses the predetermined threshold Th (here point <b>773</b>A, <b>773</b>B) as it heads toward and away from a peak of the signal <b>772</b>A (an example of such a peak is designated by reference numeral <b>771</b>), causing the output of the comparator to change from a first state (an example of which is designated by reference numeral <b>776</b>) to a second state (an example of which is designated by reference numeral <b>774</b>), and then back to the first state <b>776</b>. The first and second states <b>776</b>, <b>774</b> of the predetermined threshold detector output signal <b>740</b>A are separated by positive and negative edges (examples of which are designated respectively by reference numerals <b>775</b>A and <b>775</b>B). In the same or different embodiment, the predetermined threshold Th includes a first predetermined threshold (i.e., predetermined threshold at point <b>773</b>A) and a second predetermined threshold (for example, predetermined threshold at point <b>773</b>C) which induce the first and second states <b>776</b>, <b>774</b>.

0106In some embodiments, the first and second states <b>776</b>, <b>774</b> of the predetermined threshold detector output signal <b>740</b>A are responsive to a time-varying magnetic field associated with an object and sensed by a pair of magnetic field sensing elements (as may be similar to first pair of magnetic field sensing elements <b>205</b>A described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>), which provides the signal <b>772</b>A. The magnetic field signal <b>772</b>A exhibits a pattern (which is shown here for simplicity to be a sinusoidal pattern) related to the time-varying magnetic field produced by the object as it moves past the magnetic field sensing elements (and, more particularly, as portions of the object, such as gear teeth <b>224</b>A, <b>224</b>B, <b>224</b>C of object <b>224</b>, move past the magnetic field sensing elements). The first and second states <b>776</b>, <b>774</b> of the predetermined threshold detector output signal <b>740</b>A can be said to encode the cycles of the pattern and, in this way, are indicative of object movement that induces the pattern. In some embodiments, the second state <b>774</b> is related to portions of the object (such as a subset of the gear teeth having a north or south polarity) as they move past the magnetic field sensing elements. In some embodiments, the magnetic field signal <b>772</b>A saturates (examples of which are designated by reference numerals <b>779</b>A and <b>779</b>B).

0107Another portion <b>700</b>B of the graph <b>700</b> includes a time-varying magnetic field signal <b>772</b>B representative of, for example, the magnetic field signal <b>282</b>B of <figref idref="DRAWINGS">FIG. 2</figref>. The magnetic field signal <b>772</b>B is responsive to a magnetic field associated with the movement of an object, as may be similar to object <b>224</b> described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>.

0108Graph <b>700</b> (at portion <b>700</b>C) includes a predetermined threshold detector output signal <b>740</b>B representative of, for example, the predetermined threshold detector output signal <b>240</b>B output from predetermined threshold detector <b>220</b>B of <figref idref="DRAWINGS">FIG. 2</figref>. In operation, the predetermined threshold detector output signal <b>740</b>B is representative of the output of a comparator (as may be similar to comparator <b>228</b>B described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>) coupled at a first input to the magnetic field signal <b>772</b>B and at a second input to a reference voltage representative of a predetermined threshold Th. The magnetic field signal <b>772</b>B crosses the predetermined threshold Th (here points <b>783</b>A, <b>783</b>B) as it heads toward and away from a peak of signal <b>772</b>B (an example of such a peak is designated by reference numeral <b>781</b>) causing the output of the comparator to change from a first state (an example of which is designated by reference numeral <b>786</b>) to a second state (an example of which is designated by reference numeral <b>784</b>), and then back to the first state <b>776</b>. The first and second states <b>786</b>, <b>784</b> of the predetermined threshold detector output signal <b>740</b>B are separated by positive and negative edges (examples of which are designated respectively by reference numerals <b>785</b>A and <b>785</b>B).

0109In some embodiments, the first and second states <b>786</b>, <b>784</b> of the predetermined threshold detector output signal <b>740</b>B are responsive to a time-varying magnetic field associated with an object and sensed by a pair of magnetic field sensing element (as may be similar to second pair of magnetic field sensing elements <b>205</b>B described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>), which provides the signal <b>772</b>B. The magnetic field signal <b>772</b>B exhibits a pattern (which is shown here for simplicity to be a sinusoidal pattern) related to the time-varying magnetic field as the object moves past the magnetic field sensing elements (and, more particularly, as portions of the object, such as gear teeth <b>224</b>A, <b>224</b>B, <b>224</b>C of object <b>224</b>, move past the magnetic field sensing elements). The first and second states <b>786</b>, <b>784</b> of the predetermined threshold detector output signal <b>740</b>B can be said to encode cycles of the pattern and, in this way, are indicative of object movement that induces the pattern. In some embodiments, the second state <b>784</b> is related to portions of the object (such as a subset of the gear teeth having a north or south polarity) as they move past the magnetic field sensing elements.

0110An edge rate or period of the predetermined threshold detector output signals <b>740</b>A, <b>740</b>B are indicative of a speed of object movement. In other words, higher edge rates correspond to relatively fast object movement and lower edge rates correspond to relatively slow object movement. In embodiments in which the object is a rotating gear, signal frequency is indicative of rotation speed of the gear.

0111In <figref idref="DRAWINGS">FIG. 7</figref>, an orientation of triangular icons <b>777</b> is indicative of a direction of object movement. As can be seen in graph <b>700</b>, all of the icons are oriented toward the right-hand side of the paper indicating that the object is moving in the same direction over the entire graphed time. Furthermore, the predetermined threshold detector output signals <b>740</b>A, <b>740</b>B can be said to have a relative phase. The relative phase sequences of rising and falling edges can be used to determine a direction of object movement. In embodiments in which the object is a rotating gear, icon direction is indicative of clockwise or counter-clockwise rotational movement of the gear.

0112Referring now to <figref idref="DRAWINGS">FIG. 8</figref>, a graph <b>800</b> has a horizontal axis with a scale in arbitrary units of time and a vertical axis in arbitrary units of voltage. One portion <b>800</b>A of the graph <b>800</b> includes a time-varying magnetic field signal <b>872</b>A representative of, for example, the magnetic field signal <b>272</b>A of <figref idref="DRAWINGS">FIG. 2</figref>. The magnetic field signal <b>872</b>A is responsive to a magnetic field associated with the movement of an object, as may be similar to object <b>224</b> described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>. In normal operation, a PDAC signal <b>874</b>A, which may be representative of the PDAC signal <b>402</b> described in conjunction with <figref idref="DRAWINGS">FIG. 3</figref>, can acquire and track positive peaks (an example of which is designated by reference numeral <b>871</b>A). The PDAC signal <b>874</b>A attempts to track the magnetic field signal <b>872</b>A between various times in the cycle, for example, between times t₁and t₂, eventually achieving a positive peak of the magnetic field signal <b>872</b>A at about time t₅, which may be within about three cycles (or over a time period which may be related to a rotation speed of the detection target) of the magnetic field signal <b>872</b>A. The PDAC signal <b>874</b>A holds at other times.

0113It should be noted that the PDAC signal <b>874</b>A is generated at times before achieving a positive peak of the magnetic field signal <b>872</b>A (such times denoted by dashed line box <b>890</b>A), but is inaccurate and does not represent the true motion detection information and so is not shown in <figref idref="DRAWINGS">FIG. 8</figref>. It should also be noted that in some embodiments, PDAC signal <b>874</b>A is released just before positive peaks of magnetic field signal <b>872</b>A (for example, just before positive peak <b>871</b>A) and tracks the magnetic field signal <b>872</b>A as it acquires the peak.

0114Similarly, an NDAC signal <b>876</b>A, which may be representative of the NDAC signal <b>406</b> described in conjunction with <figref idref="DRAWINGS">FIG. 3</figref>, can acquire and track negative peaks (an example of which is designated by reference numeral <b>881</b>A). The NDAC signal <b>876</b>A attempts to track the magnetic field signal <b>872</b>A between various times in the cycle, for example, between times t₃and t₄, eventually achieving a negative peak of the magnetic field signal <b>872</b>A at about time t₆, which may also be within about three cycles of the magnetic field signal <b>872</b>A. The NDAC signal <b>876</b>A holds at other times.

0115It should be noted that the NDAC signal <b>876</b>A is generated at times before achieving a negative peak of the magnetic field signal <b>872</b>A (such times denoted by dashed line box <b>892</b>A), but is inaccurate and does not represent the true motion detection information and so is not shown in <figref idref="DRAWINGS">FIG. 8</figref>. It should also be noted that in some embodiments, NDAC signal <b>876</b>A is released just before negative peaks of magnetic field signal <b>872</b>A (for example, just before negative peak <b>881</b>A) and tracks the magnetic field signal <b>872</b>A as it acquires the peak.

0116Another portion <b>800</b>B of the graph <b>800</b> includes a time-varying magnetic field signal <b>872</b>B representative of, for example, the magnetic field signal <b>282</b>A of <figref idref="DRAWINGS">FIG. 2</figref>. The magnetic field signal <b>872</b>B is responsive to a magnetic field associated with the movement of an object, as may be similar to object <b>224</b> described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>. In normal operation, a PDAC signal <b>874</b>B, which may be representative of the PDAC signal <b>402</b> described in conjunction with <figref idref="DRAWINGS">FIG. 3</figref>, can acquire and track positive peaks (an example of which is designated by reference numeral <b>871</b>B). The PDAC signal <b>874</b>B attempts to track the magnetic field signal <b>872</b>B between various times in the cycle, for example, between times t₇and t₈, eventually achieving a positive peak of the magnetic field signal <b>872</b>A at about time t₁₁, which may be within about three cycles of the magnetic field signal <b>872</b>A. The PDAC signal <b>874</b>B holds at other times.

0117It should be noted that the PDAC signal <b>872</b>B is generated at times before achieving a positive peak of the magnetic field signal <b>872</b>B (such times denoted by dashed line box <b>890</b>B), but is inaccurate and does not represent the true motion detection information and so is not shown in <figref idref="DRAWINGS">FIG. 8</figref>. It should also be noted that in some embodiments, PDAC signal <b>872</b>B is released just before positive peaks of magnetic field signal <b>872</b>B (for example, just before positive peak <b>871</b>B) and tracks the magnetic field signal <b>872</b>B as it acquires the peak.

0118Similarly, an NDAC signal <b>876</b>B, which may be representative of the NDAC signal <b>406</b> described in conjunction with <figref idref="DRAWINGS">FIG. 3</figref>, can acquire and track negative peaks (an example of which is designated by reference numeral <b>881</b>B). The NDAC signal <b>876</b>B attempts to track the magnetic field signal <b>872</b>B between various times in the cycle, for example, between times t₉and t₁₀, eventually achieving a negative peak of the magnetic field signal <b>872</b>B at about time t₁₂, which may also be within about three cycles of the magnetic field signal <b>872</b>B. The NDAC signal <b>876</b>B holds at other times.

0119It should be noted that the NDAC signal <b>876</b>B is generated at times before achieving a negative peak of the magnetic field signal <b>872</b>B (such times denoted by dashed line box <b>892</b>B), but is inaccurate and does not represent the true motion detection information and so is not shown in <figref idref="DRAWINGS">FIG. 8</figref>. It should also be noted that in some embodiments, NDAC signal <b>876</b>B is released just before negative peaks of magnetic field signal <b>872</b>B (for example, just before negative peak <b>881</b>B) and tracks the magnetic field signal <b>872</b>B as it acquires the peak.

0120Another portion <b>800</b>C of the graph <b>800</b> includes a tracking threshold detector output signal <b>745</b>A representative of, for example, the tracking threshold detector output signal <b>245</b>A output from tracking threshold detector <b>210</b>A of <figref idref="DRAWINGS">FIG. 2</figref>. In operation, the tracking threshold detector output signal <b>745</b>A is representative of the output of a comparator (as may be similar to comparator <b>218</b>A described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>) coupled at a first input to the magnetic field signal <b>872</b>A and at a second input to a tracking signal, as may be similar to the tracking signal <b>277</b>A output from tracking circuit <b>216</b>A and described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>.

0121The tracking threshold output signal <b>745</b>A has edges <b>747</b>A, <b>747</b>B that align with positive and negative peaks, respectively, of the magnetic field signal <b>872</b>A. It can be seen in <figref idref="DRAWINGS">FIG. 8</figref> that at some time (e.g., at about t₆), edges of the tracking threshold output signal <b>745</b>A will align to a peak-to-peak magnitude of the magnetic field signal <b>872</b>A, at which time the tracking threshold detector can be said to be calibrated to the magnetic field signal <b>872</b>A (i.e., the tracking threshold detector output signal <b>745</b>A will accurately track the positive and negative peaks of the magnetic field signal <b>872</b>A). The tracking threshold output signal <b>745</b>A is generated at times before it aligns to the peak-to-peak magnitude of the magnetic field signal <b>872</b>A (such times denoted by dashed line box <b>893</b>), but is not used and so is not shown in <figref idref="DRAWINGS">FIG. 8</figref>.

0122Portion <b>800</b>C of the graph <b>800</b> also includes a tracking threshold detector output signal <b>745</b>B representative of, for example, the tracking threshold detector output signal <b>245</b>B output from tracking threshold detector <b>210</b>B of <figref idref="DRAWINGS">FIG. 2</figref>. In operation, the tracking threshold detector output signal <b>745</b>B is representative of the output of a comparator (as may be similar to comparator <b>218</b>B described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>) coupled at a first input to the magnetic field signal <b>872</b>B and at a second input to a tracking signal, as may be similar to the tracking signal <b>277</b>B output from tracking circuit <b>216</b>B described in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>.

0123Similarly to the above-described signal <b>745</b>A, the tracking threshold output signal <b>745</b>B has edges <b>757</b>A, <b>757</b>B that align with positive and negative peaks, respectively, of the magnetic field signal <b>872</b>B. It can be seen in <figref idref="DRAWINGS">FIG. 8</figref> that at some time (e.g., at about t₁₂), edges of the tracking threshold output signal <b>745</b>B will correspond to a peak-to-peak magnitude of the magnetic field signal <b>872</b>B, at which time the tracking threshold detector can be said to be calibrated to the magnetic field signal <b>872</b>B (i.e., the tracking threshold detector output signal <b>745</b>B will accurately track the positive and negative peaks of the magnetic field signal <b>872</b>B). The tracking threshold output signal <b>745</b>B is generated at times before it aligns to the peak-to-peak magnitude of the magnetic field signal <b>872</b>B (such times denoted by dashed line box <b>893</b>), but is not used and so is not shown in <figref idref="DRAWINGS">FIG. 8</figref>.

0124In <figref idref="DRAWINGS">FIG. 8</figref>, triangular icons (an example of which is designated by reference numeral <b>877</b>) are indicative of speed and direction of object movement. An edge rate or period of the tracking threshold detector output signals <b>745</b>A, <b>745</b>B indicative of a speed of object movement. In other words, higher edge rates correspond to relatively fast object movement and lower edge rates correspond to relatively slow object movement. In embodiments in which the object is a rotating gear, signal frequency is indicative of rotation speed of the gear.

0125In <figref idref="DRAWINGS">FIG. 8</figref>, the orientation of triangular icons <b>877</b> is indicative of a direction of object movement. As can be seen in graph <b>800</b>, a first triangular icon <b>877</b>A is shown in phantom relief to indicate that although the directional output is generated it is inaccurate and so the directional information may be generated from the predetermined threshold detectors. The other icons (for example, icon designated by reference numeral <b>877</b>B) are oriented toward the right-hand side of the paper. As may be the same or similar to the circuit arrangement described above in conjunction with <figref idref="DRAWINGS">FIG. 2</figref>, the first and second tracking threshold detector output signals <b>745</b>A, <b>745</b>B are responsive to object movement relative to offset magnetic field sensing elements (such as magnetic field sensing elements <b>204</b>A, <b>204</b>B). Accordingly, a relative phase sequence of rising and falling edges of the signal <b>745</b>A, <b>745</b>B is representative of object movement direction.

0126Successive edge <b>760</b>C and edge <b>760</b>B may be used to accurately determine and update the direction of object movement (as can be seen by triangular icon <b>877</b>B and all successive icons). In embodiments in which the object is a rotating gear, icon direction is indicative of clockwise or counter-clockwise rotational movement of the gear.

0127Referring again to <figref idref="DRAWINGS">FIGS. 7 and 8</figref>, it can be seen that correct object movement information (in particular, direction of object movement) can be generated at a time near circuit start up or power up at time t₀using the predetermined threshold detector output signal (<b>740</b>A, <b>740</b>B). For example, correct object movement direction information using the predetermined threshold detector output signal (<b>740</b>A, <b>740</b>B) can be generated quickly after time t₀at time t₀₁. The correct object movement direction information using the tracking threshold detector output signal (<b>745</b>A, <b>745</b>B) can be generated later than time t₀₁at time t₀₂. At least a portion of the time difference can be attributed to the time required to calibrate the tracking threshold detectors. In contrast, the predetermined threshold detectors can generate object movement direction information whenever the magnetic field signal crosses the predetermined threshold values (e.g., <b>773</b>A, <b>773</b>B or <b>773</b>A, <b>773</b>C), which can occur relatively soon after a start up or power up period of the circuit.

0128Referring now to <figref idref="DRAWINGS">FIG. 9</figref>, first graph <b>900</b>A has a horizontal axis with a scale in arbitrary units of time and a vertical axis in arbitrary units of voltage. Graph <b>900</b>A includes a first predetermined threshold detector output signal <b>940</b>A representative of, for example, the predetermined threshold detector output signal <b>240</b>A output from the predetermined threshold detector <b>220</b>A of <figref idref="DRAWINGS">FIG. 2</figref>, and a second predetermined threshold detector output signal <b>940</b>B representative of, for example, the predetermined threshold detector output signal <b>240</b>B output from the predetermined threshold detector <b>220</b>B of circuit <b>200</b> of <figref idref="DRAWINGS">FIG. 2</figref>. Graph <b>900</b>A also includes a first tracking threshold detector output signal <b>945</b>A representative of, for example, the tracking threshold detector output signal <b>245</b>A output from the tracking threshold detector <b>210</b>A of <figref idref="DRAWINGS">FIG. 2</figref>, and a second tracking threshold detector output signal <b>945</b>B representative of, for example, the tracking threshold detector output signal <b>245</b>B output from the tracking threshold detector <b>210</b>B of circuit <b>200</b> of <figref idref="DRAWINGS">FIG. 2</figref>.

0129A second graph <b>900</b>B has a horizontal axis with a scale in arbitrary units of time and a vertical axis to indicate selected output information (an example of which is designated by reference number <b>955</b>) related to one of the signals <b>940</b>A, <b>940</b>B, <b>945</b>A, <b>945</b>B of graph <b>900</b>A. The selected output information <b>955</b> relates to movement of an object, as may be the same or similar to object movement information (e.g., speed and direction of object movement) described above in conjunction with <figref idref="DRAWINGS">FIG. 7</figref> and <figref idref="DRAWINGS">FIG. 8</figref>.

0130For example, at time t₂₁, the selected object speed information <b>955</b>A is related to the signal <b>940</b>A and at time t₂₄the selected object speed information <b>955</b>B is related to signal <b>945</b>A. Here, during circuit start up or power up, an output signal selector (as may be the same or similar to output selector <b>250</b> of circuit <b>200</b> of <figref idref="DRAWINGS">FIG. 2</figref>) selects one of the predetermined threshold detector output signals (e.g., the first predetermined threshold detector output signal <b>940</b>A) to generate speed information and at time t₂₄selects one of the tracking threshold detector output signal (e.g., the first tracking threshold detector <b>945</b>A) to generate speed information.

0131At time t₂₂, the selected object direction information <b>955</b>C is derived from signals <b>940</b>A, <b>940</b>B and at time t₂₃the selected object direction information <b>955</b>D is derived from signals <b>945</b>A, <b>945</b>B. Here, during circuit start up or power up, the output signal selector selects relative phases of the predetermined threshold detector output signals (e.g., predetermined threshold detector output signals <b>940</b>A, <b>940</b>B) to derive direction information and at time t₂₃selects relative phases of the tracking threshold detector output signals (e.g., the tracking threshold detector signals <b>945</b>A, <b>945</b>B) to derive direction information. Time t₂₃(i.e., a time when output selector <b>250</b> of circuit <b>200</b> of <figref idref="DRAWINGS">FIG. 2</figref> switches from using the predetermined threshold detectors <b>220</b>A, <b>220</b>B to using the tracking threshold detectors <b>210</b>A, <b>210</b>B) may correspond to a predetermined condition including, but not limited to, a calibration time of a circuit and/or a predetermined number of cycles of one of the signals <b>940</b>A, <b>940</b>B, <b>945</b>A, <b>945</b>B. Triangular icons <b>977</b> represent object direction information output by the output signal selector related to the first and second predetermined threshold detector output signals <b>940</b>A, <b>940</b>B, and triangular icons <b>979</b> represent object direction information output by the output signal selector related to the first and second tracking threshold detector output signals <b>945</b>A, <b>945</b>B.

0132It will be appreciated that, in order to obtain a rapid determination of direction of movement, two predetermined threshold detectors should be used, so that a relative phase can be rapidly determined between the output signals of the two predetermined threshold detectors. However, use of only one predetermined threshold detector as in <figref idref="DRAWINGS">FIG. 1</figref> can still provide advantages, for example, a more rapid determination of object speed of movement (see, e.g., selected output information <b>955</b> beginning at time t₂₁).

0133While particular numbers of cycles, particular times, and other particular parameters are described above, it will be appreciated that other numbers of cycles, other times, and other particular parameters can be used.

0134It should be appreciated that a circuit as described herein may be used in applications in which it is desired, needed, or necessary to generate fast speed and/or direction information in sensor applications including, but not limited to, automotive engine management applications.

0135All publications and references cited herein are expressly incorporated herein by reference in their entirety.

0136Having described embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating these concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims.