Crystal oscillator emulator

The present invention relates to a voltage controlled oscillator (VCO).

Accurate frequency references are required in many types of electronic devices such as mobile phones and other mobile devices. Crystal oscillators are generally used to provide accurate frequency references for these electronic devices. However, crystal oscillators have some inherent disadvantages, including large bulk size, brittleness and high cost. Also, the size and cost of a crystal oscillator is related to the resonance frequency, so the cost and brittleness can increase rapidly as the frequency increases and decreases. As the size of electronic devices continues to decline, the use of crystal oscillators becomes a problem due to size, fragility and cost limits.

Semiconductor oscillators are an inadequate alternative to crystal oscillators and are generally unsuitable for use as accurate frequency references due to excessive changes in oscillation frequency, especially temperature changes.

<p> An object of the present invention is to provide a voltage controlled oscillator.</p>

<p> In order to solve the above problems, in the embodiment of the present invention, an apparatus that generates an output signal having a frequency and has a die temperature is provided. The device includes a first temperature sensor that detects the first temperature, a non-volatile memory that stores calibration information for controlling the output signal frequency as a function of the first temperature, and a function of the calibration information for the output signal. It is provided with a semiconductor oscillator generated as.</p><p> One or more embodiments of the present invention will be described in detail with reference to the accompanying drawings and the description below. Other features, objects and effects of the present invention will be apparent from the description and drawings, as well as the claims.</p>

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention within the scope of the claims, and all combinations of features described in the embodiments are included. It is not always essential for the means of solving the invention.

FIG. 1 shows an embodiment of a crystal oscillator emulator 10 for generating an output signal 12 having an accurate frequency. The crystal oscillator emulator 10 can be built on a single semiconductor die using any process, including a complementary metal oxide semiconductor (CMOS) process.

The crystal oscillator emulator 10 may include a semiconductor oscillator 14 to generate the output signal 12. Any type of semiconductor oscillator can be used, including LC oscillators, RC oscillators and ring oscillators. The semiconductor oscillator 12 includes a control input 16 for changing the frequency of the output signal. The control input 16 may also be any electrical input that results in a controlled change in the output signal frequency, such as the supply voltage of the ring oscillator, and a voltage input to the varicap of the LC oscillator.

The non-volatile memory 18 contains calibration information 20 for controlling the output signal frequency as a function of temperature. Any type of non-volatile memory can also employ an associative storage device (CAM). The calibration information 20 may include a correction factor applied to the control input 16 of the semiconductor oscillator 14 to control the output signal frequency. The calibration information 20 may be a function of temperature change from the calibration temperature to the operating temperature as well as a function of absolute temperature.

The temperature sensor 22 can sense the temperature of the semiconductor die. The temperature sensor is preferably located on the semiconductor die near the semiconductor oscillator 14. Any type of temperature sensor 22 may include a thermistor and an infrared detector. The temperature sensor 22 can be configured to measure a change in temperature from a reference temperature or a current temperature.

FIG. 2 shows a storage method 30 in which the calibration information 20 is stored in the non-volatile memory 18. Storage scheme 30 can be any form of database, including CAM, index schemes, lookup tables and hash tables.

FIG. 3 shows an example of a typical graph 32 of the temperature vs. correction coefficient value for maintaining a constant output signal frequency in the crystal oscillator emulator 10. The data constituting the curve can be obtained by any method including device level test and batch mode test.

A typical device level test may include testing each device to determine the correction factor applied to the semiconductor oscillator to maintain a constant output frequency with temperature changes. In one scheme, the reference value for the control input of the semiconductor oscillator is determined for a predetermined frequency and at a predetermined temperature of the semiconductor die of the device, such as the minimum operating temperature. The reference value can be determined directly from the measurement of the characteristics of other devices or by the interpolation method. The reference value can also be determined for each possible output frequency. Further, the reference value for each potential output frequency can be obtained by extrapolation from the reference value for a predetermined frequency using a known circuit relationship. The reference value for each possible output frequency can be stored as an absolute value or as a ratio, frequency coefficient to calculate the reference value from a single reference value.

The temperature of the semiconductor die is increased from the lowest operating temperature to the maximum operating temperature by discrete steps. The number of discrete steps is preferably limited to about 6 temperatures to reduce test costs, but any number of discrete steps can also be used. Although it is desirable to use an on-chip heater to heat the semiconductor die, any means of varying the temperature of the semiconductor die can also be used. At each discrete step, the semiconductor die temperature and correction factor to maintain a constant frequency output can be measured.

The correction coefficient is preferably a ratio applied to the reference value in order to obtain a compensation value or a correction value for the control input. The calibration factor can also vary from any reference value such as 1. It is preferred that a single correction factor applied to the semiconductor oscillator to keep the output signal at any one of a number of predetermined frequencies be calculated for each temperature step. For example, if the correction factor of 1.218 is determined to correspond to a temperature change of 45 ° C, the control input of the semiconductor oscillator is adjusted as a function of the correction factor by changing the control input in proportion to the correction factor. obtain. Alternatively, the correction factor may be applied to a reference value corresponding to the desired output frequency so that the control input produces an adjusted adjustment value. Alternatively, the correction factor can be measured corresponding to each of several output frequencies at each temperature step.

Batch mode testing of the crystal oscillator emulator 10 to obtain calibration information 20 can conveniently reduce costs by reducing the number of measurements for a batch of semiconductor dies. In batch mode testing, test results for a subset of crystal oscillator emulators 10 from the same batch of semiconductor dies can be used for all of the batch equipment. The subset of crystal oscillator emulators tested can vary from 1 to any portion of the total amount of equipment. For example, a single crystal oscillator emulator 10 is tested and the resulting batch calibration information can be stored in each of the devices in the batch. Note that each crystal oscillator emulator 10 can be tested for a subset of calibration information such as output frequency at reference temperature. A subset of instrument-specific calibration information can be used to modify the batch calibration information stored in each instrument.

FIG. 4 shows another aspect of the crystal oscillator emulator 40. The crystal oscillator emulator 40 is a corresponding element numbered 40-52, except that the crystal oscillator emulator 40 may include one or more heaters 54, controllers 56 and selective inputs 58 alone or in combination. The function of is similar to that of the crystal oscillator 10.

The heater 54 may be located on the semiconductor die near the semiconductor oscillator 44 to provide a partial heating source. Any type of heater 54 may be used, including transistor heaters and electric resistance heaters. The heater 54 may be operated in response to an input from the temperature sensor 42 to control the temperature of the semiconductor die. The heater 54 may increase the semiconductor die temperature to a level corresponding to one of the temperature levels for which the correction factor has been determined. Also, a package with high thermal impedance can surround the crystal oscillator emulator 40.

In one case, the heater 54 may raise the semiconductor die temperature to the maximum operating temperature. Here, during equipment or batch level testing, only the correction factors corresponding to the maximum operating temperature will have to be determined. This reduces costs.

The heater 54 can also be controlled to raise the semiconductor die temperature to one of several predetermined temperature levels for which a correction factor has been determined. The second temperature sensor can sense external temperatures such as ambient temperature or device temperature. During temperature changes, the heater 54 can raise the semiconductor die temperature to the one closest to a predetermined temperature level while continuously changing the control input using an estimate calculated from the correction factors.

The controller 56 may add additional functionality, for example, by controlling the heater 54 in response to a large number of temperature sensors or by manipulating the calibration information 50 to obtain values for control inputs corresponding to intermediate temperatures. The controller 56 may be of any kind of element, including processors, logic circuits and software modules.

Selective input 58 can be used to select a particular output frequency within the range of output frequencies. The output frequency can be chosen as a function of the impedance of the external component connected to the selective input. The external component may be used directly as a part of a semiconductor oscillator that selects an output frequency, or may be used indirectly, such as selecting an impedance value within a predetermined range corresponding to a predetermined output frequency. The external component may be any component, but is preferably a passive element such as a register or capacitor.

FIG. 5 shows, for example, an embodiment of a crystal oscillator emulator 100 with two selection pins 102 and 104 connected to two external impedances 106 and 108. One or more pins can be used to interface with external components. The crystal oscillator emulator 100 looks up or retrieves information from external components connected to selection pins 102 and 104. Derived information can have three or more predetermined level ranges that correspond to selected levels of emulator features. For example, a single pin connected to an external register can be used to select any one of the 16 output frequency levels. The resistance of the external register is preferably selected from one of 16 predetermined standard values. Each of the 16 values of the resistor corresponds to one of the 16 output frequency levels. It should be noted that the low precision passive element is preferably used as an external component in order to reduce cost and inventory. Each external component can have a predetermined nominal value of N, which is a multiple of each corresponding to the selection of a given characteristic level. If one pin is used, different characteristic levels of N can be chosen. When two pins are used, different characteristic levels of N * N can be selected to accommodate the increasing number of selected pins. For example, the types of device features that can be selected include output frequency, frequency tolerance, and reference correction factor. For example, the crystal oscillator emulator 100 may include a single selection pin 102 connected to an external register that can have a nominal value chosen from a group of 16 predetermined values. Each of the 16 predetermined values has a measured range corresponding to one of 16 predetermined output frequency levels from 1 MHz to 100 MHz.

The external impedances 106 and 108 are preferably registers, capacitors, or combinations of registers and capacitors, and can be any component, primarily including inductance, resistance, capacitance, or a combination thereof. External impedances 106 and 108 can be connected directly or indirectly from energy sources such as Vdd and ground or appropriate references to pins 102 and 104. For example, the external impedance 106 can be connected to Vdd by a register / transistor network and to selection pin 102 by a capacitor network.

The crystal oscillator emulator 100 may determine a predetermined selection value corresponding to a measurement of impedance connected to the selection pin. Impedance is chosen to have standard values such as nominal resistance for registers with a 10% tolerance (eg, 470, 560, 680, ...) to reduce equipment and inventory costs. Is preferable. To illustrate the tolerance of measurement and the tolerance of external impedance, the impedance value range may correspond to a single selection value. The selected value is preferably a digital value, but may be an analog value. For example, a measured resistance value from 2400 ohms to 3000 ohms can be associated with a digital value corresponding to 2. The value of the measured resistor from 3001 ohms to 4700 ohms is associated with the digital value corresponding to 3. The measurement resistance includes fluctuations depending on the external impedance and the allowable range of the built-in measurement circuit. The impedance measured at each selection pin is used to determine the corresponding digital value. The range of digital values includes 3 or more digital values, preferably 10 to 16 digital values per selection pin. The digital value corresponding to each selection pin can be used in connection with representing a memory address. For example, a device with three selection pins each interfacing an impedance value that maps to one of ten digital values can represent 1000 memory addresses or a look-up table. The contents of the storage location corresponding to the memory address are used to set values for the output or internal characteristics of the device. A typical other device can include two selection pins, each configured to interface an external impedance that maps to a digital value within the range of 10 values. The digital values of the combination can represent 100 memory addresses or look-up tables, each of which may contain data for setting the features of the crystal oscillator emulator 100.

FIG. 6 shows a block diagram of an embodiment of the crystal oscillator emulator 120. The crystal oscillator emulator 120 includes a selection pin 122 that interfaces an external impedance 124 used to select the configuration of the crystal oscillator emulator 120. The external impedance 124 is similar to the external impedances 116 and 118 in terms of function and range.

The measurement circuit 126 connected to the selection pin 122 measures electrical features that are a function of the external impedance 124. For example, current can be supplied to the external impedance and the voltage measured across the external impedance 124. Also, the voltage is determined across the external impedance 124, from which the current can be measured. Any measurement technique for measuring passive devices can also be used to measure electrical features, including static and dynamic techniques. Typical measurement techniques include timing circuits, analog-to-digital converters (ADCs) and digital-to-analog converters (DACs). The measurement circuit preferably has a high dynamic range. The measurement circuit 126 may generate an output having a value corresponding to the value of the external impedance 124. The output may be digital or analog. The same output value represents a range of external impedance values to compensate for value fluctuations such as external impedance value tolerances, interconnection losses and measurement circuit tolerances due to factors including process, temperature and power. Is preferable. For example, all measured external impedance values in the 22-32 ohm range can correlate to a digital output value of "0100". On the other hand, the measured external impedance value in the range of 32 to 54 ohms can correlate with the digital output value of "0101". The actual external impedance value is a subset of the external impedance value measured to account for the value variation. For example, in the above case, the actual external impedance values can be 24-30 ohms and 36-50 ohms. In each case, inexpensive low precision registers may be chosen to have values such as 27 ohms and 43 ohms as the median of the range. In this way, inexpensive low precision components can be utilized to be selected in the range of high precision output. The selection value can be used directly as a variable value for controlling the device characteristics of the crystal oscillator emulator 120. The variable value can also be determined indirectly from the selected value.

The storage circuit 127 may include a variable value that can be chosen as a function of the selection value. The storage circuit 127 may be any storage structure including an associative storage device, static and dynamic memory, and a look-up table.

If the measurement circuit 126 produces an output value that has a one-to-one correspondence with an external impedance value, the digital value determinant 128 sets the output value to a selection value that corresponds to a range of external impedance values. Can be done.

FIG. 7 (a) shows the relationship between the groups of impedance value 150 and related selection value 154. A group of impedance values 150 can have a one-to-one correspondence with a group of digital output values 152 that are converted to a selection value 154 associated with each group of impedance values 150. The impedance values from the minimum impedance value to the maximum impedance are separated into three or more groups together with each group having a nominal impedance. The nominal impedance values of each group may be chosen to have an interval between the nominal impedance values. Here, the nominal values of the group of impedance values, 27 ohms and 43 ohms, have an interval of 16 ohms. The spacing between groups of impedance values is preferably based on geometric progressions, but any mathematical relationship can also be used to set spacing between groups such as logarithmic, linear, and exponential functions. .. The spacing between impedance groups can also be based on any impedance value in the group, including nominal, mean, intermediate, start, and end values. Factors that influence the choice of group impedance range and spacing can have various tolerances such as external impedance tolerances, internal voltage and current source tolerances, and measurement circuit tolerances. The tolerance can be caused by, for example, process, temperature, and power fluctuations.

FIG. 7 (b) shows the relationship between the range of impedance values 156 and related selection values 158. The range of impedance values 156 has a direct correspondence with the selection value 158. The impedance values from the minimum impedance value to the maximum impedance are separated into three or more groups, each group having a nominal impedance. The nominal impedance values of each group may be chosen to have an interval between the nominal impedance values. Here, the nominal values of the group of impedance values, 27 ohms and 43 ohms, have an interval of 16 ohms. Such a direct correspondence between the range of impedance values 156 and associated selection values 158 can be embodied, for example, by a non-linear analog-to-digital converter (not shown).

With reference to FIG. 6, the address generator 130 may determine the memory location corresponding to the digital output value associated with the external impedance connected to the selection pin. Memory locations can be grouped in such a way as a list for single selection pins, a lookup table for two selection pins, and a third order table for three selection pins.

The controller 132 may set the device characteristics of the crystal oscillator emulator 120 as a variable value function. The variable value can be generated directly by the measurement circuit, indirectly determined from the selection value, and determined from the contents of the memory location corresponding to the external impedance value connected to the selection pin.

Selection pin 122 can be used to implement additional functions: power down (PD), power enable, mode selection, reset, and synchronization operations. In this embodiment, the selection pin 124 becomes a multipurpose selection pin 122 that embodies additional functionality and constitutes the crystal oscillator emulator 120.

In one embodiment, the first range of impedance values connected to the multipurpose selection pin 122 can be used in the configuration of the crystal oscillator emulator 120, while the operation of additional functions is added to the multipurpose selection pin 122. It can be controlled by voltage or current, or an impedance value outside the first range of impedance values.

FIG. 8 shows an aspect of the oscillator assembly 200 that produces an output with a periodic waveform. The oscillator assembly 200 includes a crystal oscillator emulator 202 to drive a phase-locked loop (PLL) 204. The crystal oscillator emulator 202 may be similar in function and structure to the aspects of the crystal oscillator emulator described above. The oscillator assembly 200 can also include any type of PLL 204, such as a digital PLL and an analog PLL.

Multipurpose selection pins 206 and 208 can be used to select operating parameters for the PLL 204, such as divider factors. Multipurpose selection pins 206 and 208 can also be used to control and operate the crystal oscillator emulator 202, such as receiving and outputting frequency selection of reference clocks for calibration. External registers 210 and 212 may be connected to multipurpose selection pins 206 and 208 to select the operating frequency. The range of values for the external registers 210 and 212 corresponds to the selection of different operating frequencies. The respective external registers 210 and 212 can be used to select one of 16 predetermined operating frequencies. According to the combination, the external registers 210 and 212 can be selected from 256 operating frequencies. To control a number of functions, the respective multipurpose selection pins 206 and 208 may receive signals in different voltage ranges. For example, one multipurpose selection pin 206 can be connected to an external register 210 where a voltage in the range 0-2 volts can be expressed to determine resistance, and the multipurpose selection pin 206 can be in the range 2-3 volts. Can receive a reference clock signal operating in. The decoder 214 can sense signals on the multipurpose selection pins 206 and 208.

FIG. 9 shows a diffusion spectrum oscillator 300 that produces an output signal with a variable frequency. The diffusion spectrum oscillator 300 includes a crystal oscillator emulator 302 connected to the PLL 304. The frequency controller connected to the crystal oscillator emulator 302 can dynamically control the output frequency of the crystal oscillator emulator 302. The frequency control device may be any device or technology, including varicaps. This device controls the bias current source of the semiconductor oscillator and controls the control input voltage applied to the resonant capacitor of the semiconductor oscillator.

FIG. 10 shows the operation of one aspect of the crystal oscillator emulator. At block 400, the semiconductor oscillator is provided to generate an output signal with a periodic waveform. At block 402, the semiconductor oscillator can be tuned to produce a constant frequency above a predetermined range of temperature. In one embodiment, calibration may include varying the temperature of the semiconductor die above a predetermined temperature range and measuring calibration information to maintain a constant output frequency. The die temperature can be measured near the semiconductor oscillator. The calibration information may include control input values vs. die temperature to maintain a constant output frequency. Calibration information can be stored in non-volatile memory on the semiconductor die. At block 404, the operating frequency can be determined by probing an external component. At block 406, the semiconductor oscillator produces an output signal with an operating frequency. At block 408, the temperature of the semiconductor die is determined near the semiconductor oscillator. At block 410, the semiconductor die may be heated or cooled to control the die temperature to one or more predetermined temperature levels. At block 412, the control input can be controlled as a function of die temperature to compensate for changes in the operating frequency of the output signal caused by temperature changes. The stored calibration information can be used to control the control input. The calibration information can be used immediately for the die temperature corresponding to the stored temperature. For other die temperatures, the control input value can be estimated from the stored calibration information. At block 414, the frequency of the output signal can dynamically fluctuate as a function of the frequency control signal.

FIG. 11 shows an aspect of the low power oscillator 320 that produces a periodic signal. The low power oscillator 320 includes a crystal oscillator emulator 322 that tunes the active silicon oscillator 324. The crystal oscillator emulator 322 is normally off to reduce power consumption. At predetermined intervals, the crystal oscillator emulator 322 is switched to a power-on state to tune the active silicon oscillator 324. The active silicon oscillator 324 consumes less power than the crystal oscillator emulator 322, so it is the entire low power oscillator 320 that operates the crystal oscillator emulator 322 intermittently and continuously the active silicon oscillator 324. Reduces power consumption. Any type of active silicon oscillator can also be used, including ring oscillators and RC oscillators. The crystal oscillator emulator 324 can be configured according to any of the aspects of the invention, as described and described herein.

Adder 326 may determine the frequency error between the active silicon oscillator output and the crystal oscillator emulator output. The controller 328 may generate a control signal based on a frequency error to control the frequency of the active silicon oscillator 324. The controller 328 can also receive temperature information from the crystal oscillator emulator 322. Temperature information can include temperatures such as semiconductor temperature and ambient temperature. The controller 328 may include calibration information for the active silicon oscillator 324 similar to the calibration information for the crystal oscillator emulator 322. Frequency errors can be used to set initial values for the control signal, and temperature information combined with active silicon oscillator calibration information can be used to update the control signal while the crystal oscillator emulator 322 is powered down. Can be used. In one embodiment, the temperature detection circuit of the crystal oscillator emulator 322 may be in a continuously powered state such that continuous temperature information can be supplied to the controller 328. The control signal 334 can be digital or analog. If the control signal is digital, a digital-to-analog converter (DAC) 330 can convert the control signal to analog.

The regulator 332 may control the power supply for the active silicon oscillator 324 to tune the operating frequency in response to the control signal 334. The supply of voltage and / or current to the active silicon oscillator 324 can be controlled. For example, the regulator 332 can control the voltage level of the supply voltage.

During operation, the active silicon oscillator 324 is normally in a state of producing a periodic output signal. The crystal oscillator emulator 322 is normally off. In the off state, all or part of the crystal oscillator emulator 322 may be powered off to save power. At a predetermined time, power is applied to the crystal oscillator emulator 322. The semiconductor oscillator of the crystal oscillator emulator 322 is adjusted by the stored calibration information. The frequency of the output signal of the crystal oscillator emulator 322 is compared with the frequency of the output signal of the active silicon oscillator 324 to determine the frequency error of the active silicon oscillator 324. The control signal 334 changes in response to a frequency error, thus causing a shift in the supply voltage from the voltage regulator 332, causing a change in the output frequency of the active silicon oscillator 324 and reducing the frequency error.

FIG. 12 shows another aspect of the low power oscillator 350 that produces a periodic signal. The low power oscillator 350 includes a crystal oscillator emulator 352 coupled with a charging pump oscillator 354. The crystal oscillator emulator 352 is turned off to reduce power consumption. With the power off, all or part of the crystal oscillator emulator 352 can be powered down. At predetermined intervals, the crystal oscillator emulator 352 can be used to power on and tune the charging pump oscillator 354. The predetermined interval can be determined as a function of circuit parameters such as operating time, semiconductor temperature change, ambient temperature change, semiconductor temperature, and supply voltage change.

The charging pump oscillator 354 may include a charging pump 356, a loop filter 358, a voltage controlled oscillator (VCO) 360, and a phase detector 362. The charging pump oscillator 354 is similar to a conventional charging pump oscillator in operation, except that the reference input of the phase detector 362 receives a reference clock signal from the crystal oscillator emulator 352.

The multiplexer 364 receives an output signal from the crystal oscillator emulator 352 and the charging pump oscillator 354. One of the output signals is selected and passed through the multiplexer 375 to the phase-locked loop 366. The phase lock loop 366 generates an output signal as a function of the output signal from the crystal oscillator emulator 352 and the charging pump oscillator 354.

During operation, the charging pump oscillator 354 is normally in a state of producing a periodic output signal. The crystal oscillator emulator 352 is normally off. In the off state, all or part of the crystal oscillator emulator 352 can be powered off to reduce power consumption. At a predetermined time, power is applied to the crystal oscillator emulator 352. The semiconductor oscillator of the crystal oscillator emulator 352 is adjusted by the stored calibration information. The output signal of the crystal oscillator emulator 352 is compared with the output signal of the charging pump oscillator 354 to determine the phase error of the charging pump oscillator 324. The VCO360 is controlled to reduce phase errors so that the output signal of the charging pump oscillator 354 is tuned to the output signal of the crystal oscillator emulator 352. One of the output signals can be selected and fed to the PLL366.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that such modified or improved forms may also be included in the technical scope of the present invention.

<figref num="1">It is a block diagram which shows the aspect of a crystal oscillator emulator.</figref><figref num="2">It is a table which shows the relationship with a temperature and a correction coefficient.</figref><figref num="3">It is a graph which shows the relationship with a temperature and a correction coefficient.</figref><figref num="4">It is a block diagram which shows the aspect of a crystal oscillator emulator.</figref><figref num="5">It is a two-dimensional drawing of the aspect of a crystal oscillator emulator connected to an external impedance.</figref><figref num="6">It is a detailed block diagram of the mode of the crystal oscillator emulator connected to the external impedance.</figref><figref num="7">(a) and (b) are drawings showing the relationship between the external impedance value and the digital value.</figref><figref num="8">It is a block diagram of the mode of an oscillator assembly for generating an output having a periodic waveform.</figref><figref num="9">It is a block diagram of the aspect of the diffusion spectrum generator.</figref><figref num="10">It is a flowchart of operation for emulating a crystal oscillator.</figref><figref num="11">It is a block diagram of the mode of a low power oscillator.</figref><figref num="12">It is a block diagram of another aspect of a low power oscillator.</figref>

Code description

10,40: Crystal oscillator emulator 14,44: Semiconductor oscillator 18,48: Non-volatile memory 20,50: Calibration information 22,42: Temperature sensor 54: Heater 56: Controller 200: Oscillator assembly 202: Crystal oscillator emulator 204: Phase Locked Loop (PLL) 206,208: Multipurpose Select Pin 210,212: External Register