Circuit for and method of load modulation in a system comprising a transmit resonant circuit and a receive resonant circuit

0001The invention relates to a method for load modulation in a compound of a Transmitting resonant circuit and a receiving oscillator circuit, wherein a voltage at an Transmitting resonant circuit by reaction to a change in voltage in a Receiving oscillator circuit is modulated.

0002Moreover, the invention relates to a circuit for load modulation in a Receiving resonant circuit with a transmitting resonant circuit is coupled transformer, with at least an inductance, a capacitor and a controllable impedance,

0003Such a method and such a circuit are per se and in particular by RFID applications (RFID = Radio Frequency Identification) is known. Under an RFID application is meant here any application in which a transmitting resonant circuit a supplied inductively coupled receiving oscillator circuit with energy and possibly via the Receiving resonant circuit data reads. Such compounds are, for example, to Object identification used, a transmitting resonant circuit of a reading device (reader) through a receiving resonant circuit a with a mark (a so-called tag) excellent responsive object and retrieves information.

0004To contact the transmitting resonant circuit of the reader generates a high frequency Magnetic field of the inductor in a a receiving resonant circuit, located near Reader is, an AC voltage is induced. The in the receiving resonant circuit induced AC voltage is rectified and used for example for Power supply of a connected to the receiving resonant circuit integrated Circuit. Moreover, from the induced AC voltage, a clock frequency derived, the or integrated circuit, that is, for example, a microprocessor and / a memory element is available as a system clock. By supplementing the Inductance of the transmitting resonant circuit and / or receiving resonant circuit with be capacity, especially with parallel capacity to resonant circuits scored resonance effects, which greatly improve the efficiency of energy transfer.

0005A transfer of data from the reader to the receiving resonant circuit (downlink) can to be carried out as by turning on and off of the magnetic field. For one Data transport in the reverse direction from the receiving resonant circuit to the reader is the so-called load modulation used, the sufficient proximity (distance less than 0.16 * presupposes wavelength) of transmitting resonant circuit and receiving resonant circuit. at sufficient proximity, to the so-called transformer coupling, in which the power consumption of the receiving coil by a reverse effect on the Transmitting resonant circuit in voltage changes at the transmitting resonant circuit maps. controlled Modulations of the load, ie the impedance of the receiving oscillator circuit, therefore call Voltage changes produced in the transmitting resonant circuit, which for data transmission be evaluated.

0006With increasing quality of the inductors used in the receiving resonant circuit, ie with increasing ratio of reactance to effective resistance, reduces the Damping of the resonant circuit and the width of the resonance curve. The usage of Coils of higher quality thus causes a higher frequency selectivity and, at the same Voltage on the reader side, a higher voltage on the day-side, which reach the communication link is increased.

0007In this connection it is known per se, the voltage at the receiving resonant circuit to reduce certain values ​​or limit (terminal voltages), where under the modulation between two voltages is reversed or switched. To be depletion layer elements between resonant circuit terminals and a reference or Ground potential. A lower terminal voltage is for example realized by that over the barrier layer components drops its forward voltage, the Voltage drop due to the exponential dependence of the current of the voltage in is a first approximation independent of power supplies. In other words, unlike an ohmic Resistance increases the voltage drop is not linear with the current flow but remains at higher currents at about the height of the forward voltage,

0008As a result, the depletion layer elements act at high coil currents as a reliable limiting the resonant circuit voltage to an associated value. This is for systems with high-Q inductors of importance in spatial Near transmitting resonant circuit and receiving resonant circuit otherwise undesirable high might cause tensions.

0009The second, upper, terminal voltage, by a reverse in series with Forward direction Zener diode to be realized, the connected or controlled is short-circuited. In short-circuited state, the limit described is at the lower clamping voltage, while in the non-short-circuited state, the Breakdown voltage of the Zener diode for an additive offset voltage ensures that in the Sum with the aforementioned forward voltages defines an upper clamping voltage. in the State shorted zener diode flows a comparatively large current from the Receiving resonant circuit out, corresponding to the loaded state of the resonant circuit. Accordingly, the current drain from the resonant circuit and the load of the The resonant circuit is reduced by opening the short circuit across the Zener diode.

0010In this known load modulation, the following problem has been observed: if when switching on the modulation, ie in limiting the resonant circuit voltage on the lower clamping voltage, just a high coil current is induced, so under these flows Circumstances on the bridge of the Zener diode and connected in the forward direction remaining from depletion layer elements, the resonant circuit voltage drops below the Terminal voltage and can also fall under a threshold of detection for Vibrations (pulses) of the resonant circuit voltage is used. It can therefore under unfavorable Phase conditions when the load occur that the voltage at the Transmitting resonant circuit due to the reaction of one or more periods by a Detection threshold is lowered, which the information transfer falsified. This can result a data loss in the transmission of information coming from the reader.

0011Namely switched modulation at a high induced coil current, so ensure the depletion layer elements for a limitation of the resonant circuit voltage to a through the barrier layer components predetermined value. The diodes act at this stage as a DC voltage source and thus do not have the required coil current Damping counter, so that the induced oscillation is changed. The result is a Broadening of the present input clock phase (pulse broadening), at least for partial cancellation of the sequential oscillation leads. It occurs characterized in appearance that at least one vibration in the amplitude is too small for a given Detection threshold.

0012Against this background, the object of the invention to provide a method and a circuit, which at least reduces this drawback.

0013This object is both a process and in a circuit of the the type mentioned in each case achieved in that the load modulation by controlled change a resonant circuit impedance is carried out, the at least one barrier layer and a component having ohmic resistance.

0014The linear current / voltage dependence falls at a current flow a finite, inverse voltage from about an ohmic resistance. In contrast to limits the barrier component tend to the voltage drop at higher Amperage current sensitive to approximately the height of the forward voltage, so that it similar to a DC voltage source acts. It has been found that precisely these Combination of barrier components and ohmic resistances advantage to a reliable voltage limitation without the described disadvantage of provides information loss in unfavorable starting conditions of load modulation.

0015Within an embodiment of the method it is preferred that changing the Resonant circuit impedance by controlled bridging of at least one Barrier layer component and / or the Ohm's Chen resistance occurs.

0016Both options provide a defined impedance change caused by a transformer inductive feedback to the transmitting resonant circuit transmits and therefore to Data transmission can be used by the tag to reader.

0017With regard to embodiments of the circuit is preferable that the controllable impedance is located between a first oscillator circuit connection and a reference potential.

0018This configuration is the potential at the resonant circuit terminal via the controllable linked impedance to the reference potential and to a certain extent on defined, from Value of the impedance dependent values ​​limited what a reproducible reliable Data transfer allowed by load modulation.

0019is also preferred that the controllable impedance is a first controllable impedance between the first oscillator circuit connection and the reference potential and a second controllable Impedance between a second oscillator circuit connection and the reference potential having.

0020This construction of a circuit for clamping the resonant circuit potentials to predetermined Values ​​provides the aforementioned advantages to a greater extent because it predetermined for a Limiting the positive and negative deviations of the oscillation circuit potentials of the reference potential provides.

0021A further preferred embodiment is characterized by a to the reference potential symmetrical arrangement and structure of the first and second controllable impedance controllable impedance from.

0022This symmetrical structure causes vibrations sign independently the same influenced and limited to equal amounts of deviations from the reference potential will. This also increases the reliability of data transmission.

0023It is also preferred that the controllable impedance further comprises a switchable bridge comprises at least one barrier layer component and / or the ohmic resistor.

0024Due to the switchable bypass is a load modulation with little effort realized.

0025It is also preferable that the switchable bypass a shunt path of a having transistor.

0026This configuration provides a particularly simple and controllable monolithically integratable Possibility of load modulation.

0027A further preferred embodiment is characterized in that the controllable Impedance at least one series circuit of a first barrier member and a having ohmic resistance.

0028If you switch to the barrier components an ohmic resistance in series so attenuates the resistance of the coil current, with a suitable dimensioning to the extent that the mentioned pulse broadening and hence the partial cancellation at least reduced becomes. Consequently, all the vibrations in amplitude are sufficiently high so that they may exceed the predetermined detection threshold.

0029It is also preferred that the series circuit in addition to the first barrier layer component having at least one second barrier layer component, with the first barrier layer component is connected in series and having a forward direction that a forward direction of the first is depletion layer component opposite.

0030This configuration allows the resonant circuit voltage at the load modulation in limit two switching states to defined values. As long as both barrier components are not bridged, occurs from a current flow when it exceeds the sum And a breakdown voltage of the forward voltage of the other barrier layer component a. however, the blocking component is bypassed, the flow of current occurs when exceeding the A forward voltage. The difference between the forward voltage and the sum of of forward voltage and breakdown voltage thus defines the modulation of Load modulation in the receiving resonant circuit.

0031A further preferred embodiment is characterized by a Zener diode as the first or second barrier layer component made.

0032Zener diodes have the advantage that it permanently in the breakdown voltage area can be operated.

0033It is also preferred that the controllable impedance is a parallel circuit composed of at least having a semiconductor device and an ohmic resistance.

0034By such an arrangement, the desired properties can be further optimized. Of the Disadvantage that undesirable at high currents through the resistor large voltages occur, are avoided by the parallel lying barrier component which the voltage appearing on the value of its forward voltage limits.

0035A further preferred embodiment is characterized by a diode as a third Depletion layer component from.

0036Alternatively, a transistor is used as a third component barrier layer derived from a Voltage drop is controlled on the ohmic resistance and its Operating current path at least bridges the ohmic resistance.

0037It is preferred that the operating current path of the transistor between a Oscillator circuit connection and a reference potential.

0038This alternative has the special advantage that the current through the Operating current path directly to the reference potential, so as to Substrate terminal flows. He then no longer flows from the chain of further components first and second barrier layer components into which are thus made smaller can.

0039Further advantages result from the description and the accompanying figures.

0040It is understood that the aforementioned features and to be explained below more Not only in the particular combination indicated but also in other usable combinations or alone, without leaving the context of the present departing from the invention.

drawings

0041Embodiments of the invention are illustrated in the drawings and will be in the following description explained. The drawings show in schematic form:<dl tsize="6"><dt>Fig. 1</dt><dd>an overall system of a reader and a circuit with a Receiving resonant circuit;</dd><dt>FIG. 2</dt><dd>a known receiving resonant circuit with elements for load modulation;</dd><dt>Fig. 3</dt><dd>a desired modulation behavior;</dd><dt>Fig. 4</dt><dd>a problematic modulating behavior as in known circuits in Conjunction with receiving inductors of high quality has been observed;</dd><dt>Fig. 5</dt><dd>a first embodiment of a circuit part according to the invention; and</dd><dt>Fig. 6</dt><dd>A second embodiment of a circuit part according to the invention.</dd></dl>

0042Fig. 1 shows an overall system 10 consists of a reading device (reader) 12, and a receiving part 14, for example. An object brand (tag). The reader 12 has a transmitting resonant circuit 16, the inductive in the schematic illustration of FIG. 1 and capacitive elements 18 has elements 20th The receiver 14 has a receiving resonant circuit 22, the also at least one inductor 24 and a capacitance 26 has. Further, the Reception part 14, an interface 28 and, optionally, a control circuit 30 and / or a Memory 32.

0043Fig. 2 shows the receiving resonant circuit 22 along with details of a known Interface 28. In parallel with the parallel resonant circuit 22 of inductance 24 and capacitance 26 is a series circuit of upper first diode 34, a zener diode 36, a further Zener diode 38 and lower first diodes 40 is an intermediate zener diodes 36, 38 Reference potential terminal 42 which, for example, a ground potential for the circuit provides. The Zener diodes 36, 38 can be bridged by switches 44, 46, identified by the control circuit 30 are operated. The switches 44, 46 are preferably transistors, in particular realized as MOS transistors.

0044The upper first diodes 34 and the lower first diodes 40 are used for the sole Limiting the resonant circuit voltage between terminals 48, 50 of Receiving resonant circuit 22 when closed switches 44 and 46 and define the lower Limiting voltage. In this state, the diodes 34, 40 each define, when the potential difference between the reference potential terminal 42 and one of Terminals 48, 50 34 or 40 exceeds the sum of the forward voltages of the diodes. Therefore, the resonant circuit voltage is in bridged Zener diodes 36, 38 through this Sum of the forward voltages limited so that typically a value of 3 * 0.7 = 2.1 volts for three diodes 34, 40 sets.

0045In the case of open switches 44, 46, the potential difference between the terminal 42 must and each one of the terminals 48, 50, however, in addition, the breakdown voltage the Zener diodes 36, 38 pass before the resonant circuit voltage higher on a Level is limited. When opened switches 44.46 this limitation is assuming a breakdown voltage of 7 V to 2.1 V + 7 V = 9.1 V. This value defines the upper limitation voltage.

0046By opening and closing the switches 44, 46 modulates the control circuit 30 the value the maximum resonant circuit voltage and thus the impedance of the receiving oscillator circuit 22. As already mentioned, this modulation is formed by the impedance of the Receiving resonant circuit as a modulation of the load of the transmission resonant circuit 16 of the Prerequisite a transformer coupling (distance less 0.16 times Wavelength) in the terminal voltage of the transmission resonant circuit 16 from which to read out can be used by data from the receive part fourteenth

0047Fig. 3 shows a desired curve 52 of the resulting resonant circuit voltage in U_E on receiving oscillator circuit 22 under the influence of such a controlled load modulation the time t. The large amplitudes 54 face with open switches 44, 46 of FIG. 2 a and the small amplitudes 56 arise in closed switches 44, 46 a, which blocking Zener diodes 36, 38 are bridged in FIG. 2. With in connection with of Fig. 2 mentioned values, the value of the small amplitude 56 2.1 volts and the Value of large amplitude 54 is approximately 9.1V.

0048In reality, however, shows under adverse conditions an undesired effect, such as it is shown in Fig. 4. If when the load modulation, so the Limiting the resonant circuit voltage U_E on the lower clamp level just high Coil current is induced, so that flow under circumstances via bridging the Zener diode 36 or 38 and connected in the forward direction other Depletion layer elements 34, 40 from which the resonant circuit voltage U_E temporarily the clamp level and can also fall below a threshold 58 of the detection Vibrations (pulses) of the resonant circuit voltage U_E serves. In the illustration of FIG. 4 are those insufficiently high pulses with reference numerals 60, 62 in U_E history 64 in.

0049Usually, the control circuit 30 counts of the receiving section 14, the pulses and encoding Information for the reading device 12 by varying the length of high-periods 66 and / or low periods 68 of the envelope 70 of U_E-curve 64. It applies to "high" or "low" here on each of the absolute value of the signal level. The reading device 12 registered the length of these periods 66, 68 and reconstructs the information to be read. The faulty non-registration of pulses by the receiving part 14 leads to a Distortion of the information to be transmitted.

0050Fig. 5 shows a first embodiment of a circuit part according to the invention, with the this distortion can be at least reduced. In this case, based the subject of FIG. Fifth 3. New is on the article of Figure that in addition to the first barrier layer components 72, 74 at least one ohmic resistance 76 or 78 between a Oscillator circuit connection 48, 50 and the reference potential terminal 42 is located. A current flow via one of the ohmic resistors 76, 78 is bound with a voltage drop linked via the respective resistor 76, the 78th As a result, even under the mentioned unfavorable conditions when switching on the modulation always at least the constructed voltage drop across this resistor 76 and / or 78, resulting in a reliable detection thresholds is exceeded by 58 in Fig. 4 also in parallel Oscillation and turning on a load modulation leads. The depletion layer elements 72, 74 may the diodes 34, 40 in Fig. 3 correspond to, and / or, for example, as the base-emitter diodes of transistors having short-circuited collector-base junctions be realized.

0051Fig. Figure 6 shows a second embodiment of a circuit part according to the invention. Of the 5 subject of FIG. 6a differs from the subject matter of the FIG. By inter alia Semiconductor components 80, 81, limit the voltage drops across the resistors 76, 78th As mentioned earlier, 78 ensure the resistors 76, also at the critical turning a Load modulation when oscillation of an evaluable resonant circuit voltage amplitude. The disadvantage is that large oscillating circuit currents, such as those in the steady can state occur undesirably large voltage drops across the resistors 76, could cause 78th Also, in order to prevent this, the semiconductor components limit 80, 81 the voltage drop across the resistors 76, 78th

0052In the semiconductor device can be, for example, a diode 82, the parallel with the resistor 76 between a resonant circuit terminal 48 and the other Elements of the series circuit, so the first barrier layer 72 and the components second blocking layer devices (Zener diodes) 36 is located in FIG. 5. This is for the A semiconductor device 80 shown in Fig. 6a.

0053Alternatively, 80 can be realized as a Zener diode 84, the semiconductor device, as shown in FIG. is shown 6b.

0054Further alternatively, can also be implemented as a transistor 86, the semiconductor device, as in FIG. 6 a, in conjunction with the resistor 78 in the case of the semiconductor component illustrated 81st In one embodiment, a transistor 86, the operating current path is advantageously between each one of the resonant circuit terminals 48, 50 and the Reference potential terminal 42 connected and a control terminal 88 of the transistor 86 with the resistor 76, 78 connected. In FIG. 6 is an embodiment with a diode 82 via the resistor 76 and a transistor 86 via the resistor 78 shown. It is understood but that the execution may also be symmetrical, with both resistors 76, 78 are then supplemented by similar semiconductor devices 80 or 81st

0055A sufficiently large voltage drop across the resistor 78 then controls the conducting operating current path of the transistor 86, which an increase in current through the resistor 78 and thus the voltage drop across the resistor 78 effectively limited.

0056Because the operating current path connected directly to the reference potential terminal 42 is, the guided past the resistor 78 current no longer flows in the remaining chain from first and second barrier Baule Menten 74, 38 into which a desired sequence can be made smaller. It is understood that the transistor 86 both as may be carried out MOS transistor as a bipolar transistor.