WO2006003460A1

WO2006003460A1 - Regulation circuits, devices and methods

Info

Publication number: WO2006003460A1
Application number: PCT/GB2005/002672
Authority: WO
Inventors: Robin Wilson; David Miles
Original assignee: Innovision Research & Technology Plc
Priority date: 2004-07-06
Filing date: 2005-07-06
Publication date: 2006-01-12
Also published as: GB0415157D0

Abstract

An embodiment of the invention provides regulation circuit comprising: a first rectifier (213, 214, 215, 216), coupled to an input signal (201), and being arranged to deliver a first output signal (206); a second rectifier (800, 801) coupled to the input signal (201), and being arranged to deliver a second output signal (803); an amplifier (209) coupled to the second output signal (803) and to a reference signal (207) and being arranged to generate a third output (208) related to a difference between the reference signal (207) and the second output signal (803); and a shunt device (210, 211), coupled to the input signal and being controllable via the third output (208) to control a signal amplitude of the input signal.

Description

Regulation Circuits, Devices and Methods

Field of the Invention

This invention relates to regulation circuits, devices and methods, and more particularly, but not exclusively, to the use of specific regulation circuits within Radio Frequency Identification ("RFID") devices.

Background of the Invention

The growth and diversity of radio-frequency identification applications and the use of near field communication ('TSIFC") systems is progressing rapidly. RFID systems may comprise an RFID transceiver and RFID transponder, for example such as those described in ISO standards ISO/IEC14443 or ISCvTEC 15693. In such systems a RFID transceiver is able to both transmit a Radio Frequency ("RF") signal and receive modulated RF signals (including load modulated signals). An RFID transponder is typically responsive to an RF signal supplied by an RFID transceiver once it comes into the vicinity or range of the relevant RFID transceiver. The RFID transponder may respond for example by transmitting a new RF signal or by modulating an incoming RF field. The RFID transponder may also derive power from the RF field generated by the RFID transceiver. NFC systems comprise at least one NFC device or apparatus. Such devices typically comprise both RFID transceiver and RFID transponder functionality. The function of the NFC device will depend on its mode of operation and type of system (referred to as 'initiator' and 'target'). When in target mode the NFC device operates in similar fashion to an RFID transponder i.e. it is responsive to an RF signal supplied by a second NFC device or RFID transceiver. The response may be for example by modulation of the incoming RF field or transmission of a new RF signal. When in initiator mode the NFC device operates in similar fashion to an RFID transceiver i.e. it initiates or transmits an RF signal. Examples of NFC systems are described in ISO/IEC 18092 and ISO/EEC 21481.

In operation the RFE) transponder or NFC device/ apparatus in target mode typically needs to compensate for variations in the RF field intensity when deriving power being supplied by the corresponding transceiver or second NFC device/apparatus. Additionally an energy store is required for use during any interruption of the externally generated RF field.

Prior art systems such as those described in US 5,045,770 and US

6,134,130 address these problems through the use of regulation circuits comprising one rectifier, one shunt regulator (controlled via an amplifier) and one relatively large capacitor (required for energy storage). Such prior art systems, however, have a slow response time to variations in RF field intensity

(or alternatively to variations in the reference voltage) which means that stabilisation of the overall circuit is much more difficult. This is particularly the case where RF field intensity is highly variable.

Summary of the Invention

It is an object of the present invention to provide a regulation circuit with an improved response time. It is also an object to the present invention to provide a regulation circuit which can also be used to improve the data rate of modulated signals by an RFID transponder or NFC device/apparatus in target mode.

According to a first aspect of the present invention there is provided a regulation circuit comprising: a first rectifier coupled to an input signal, and being arranged to deliver a first output signal; a second rectifier coupled to the input signal, and being arranged to deliver a second output signal; an amplifier coupled to the second output signal and to a reference signal and being arranged to generate a third output signal related to a difference between the reference signal and the second output signal; and a shunt device coupled to the input signal and being controllable via the third output to control a signal amplitude of the input signal. According to a second aspect of the present invention there is provided a voltage regulation circuit comprising: a first rectifier coupled to an input signal, and being arranged to deliver a first output voltage; a second rectifier coupled to the input signal, and being arranged to deliver a second output voltage; an amplifier coupled to the second output voltage and to a reference voltage and being arranged to generate a third output voltage related to a voltage difference between the reference voltage and the second output voltage; and a shunt device coupled to the input signal and being controllable via the third output voltage to control a voltage level of the input signal. According to a third aspect of the present invention there is provided a regulation circuit comprising: a first arm comprising a first rectifier for rectifying an input signal and delivering a first output signal; a second arm comprising a second rectifier, for rectifying the input signal and delivering a second output signal; an amplifier for generating a difference signal related to a difference between a reference signal and the second output signal; and a shunt device for controlling the input signal based on the difference signal.

Preferred embodiments of the first, second and third aspects of the present invention provide a way of regulating an input signal wherein a first output signal is generated from a first rectifier in a first arm of a circuit and regulation of the input signal may be performed by constantly monitoring a second signal in a second arm of the circuit. The second signal in the second arm may have a similar voltage or amplitude to the output voltage generated from the first rectifier, but may not be used to generate the first output signal, and may be isolated from the first arm of the circuit by the second rectifier. Based on the measurement of the second signal as against a reference signal the voltage or amplitude of the signal in the regulation circuit may be altered by directing current through a shunt in the regulation circuit. Hence, the input signal in the first arm of the circuit may be altered by measuring the second signal in the second arm of the circuit as against a reference signal. The second arm of the circuit may have a fast response to changes in the intensity of the input signal, so that changes in the input signal can be corrected for quickly by switching the shunt, meaning that a more stable first output signal can be produced. Additionally where the regulation circuit has a faster response, such regulation circuit may also be used to effect higher modulation data rates, by the RFED transponder, than would be possible in a circuit in which only one rectifier is present.

The circuit may further include a first storing means for storing energy from the output of the first rectifier; the first storing means may be coupled to the output of the first rectifier. The circuit may also include a second storing means for storing energy from the output of the second rectifier; the second storing means may be coupled to the output of the second rectifier. The first storing means may have a greater capacity for storing energy than the second storing means.

Preferably the capacity for storing energy of the first storing means is at least 25 times greater than the capacity for storing energy of the second storing means.

Preferably the capacity for storing energy of the first storing means is at least 50 times greater than the capacity for storing energy of the second storing means.

Preferably the capacity for storing energy of the first storing means is at least 100 times greater than the capacity for storing energy of the second storing means.

The first arm of the circuit may thus additionally comprise first storing means in the form of at least one capacitor thus enabling the first arm of the circuit to store energy and 'smooth' the first output voltage during cycles of the input signal. Also, if the input signal into the circuit drops, during modulation or loss of signal, for example, the stored energy can be used to maintain the supply voltage.

The second arm of the circuit may also additionally comprise second storing means in the form of at least one capacitor thus enabling the second arm of the circuit to store energy and 'smooth' the second output voltage during cycles of the input signal. In this way, the signal in the second arm can give a representation of the signal in the first arm of the circuit.

In a preferred embodiment the discharge time-constant in the first storing means is higher than the discharge time-constant in the second storing means, preferably by at least a ratio of 25:1, more preferably by at least a ratio of 50:1 and most preferably by at least a ratio of 100: 1.

In a preferred embodiment the charging time-constant in the first storing means is higher than the discharge time-constant in the second storing means, preferably by at least a ratio of 25:1, more preferably by at least a ratio of 50:1 and most preferably by at least a ratio of 100: 1.

Furthermore, preferably, the signals in both the first and second arms of the circuit can be 'smoothed' by respective storing means such storing means, so that the signal in the second (measuring or comparing) arm of the circuit mirrors the signal in the first (supply) arm of the circuit. Then, since the energy storing capacity of the second storing means is less than the storing capacity of the first storing means (and the charging and discharging resistances are approximately equal in both arms) the second arm of the circuit has a faster response to changes in the input signal than the first arm of the circuit. This means that changes in the input signal can be detected, and corrected by operating the shunt device more quickly than in the prior art. In addition and more preferably within RFID transponders, such a regulation circuit can additionally be used to facilitate modulation at higher data rates than in the prior art.

In preferred embodiments of the regulation circuit within an RFED transponder, the capacity of the first storing means is larger than that of the second storing means. This results from a requirement to have at least one large capacitor to act as an energy store. Such an energy store is required for example during periods of interruption of RF energy field or for when the RFID transponder momentarily moves out of range of the RF energy field.

The first storing means may include a first capacitor, and the second storing means may include a second capacitor, and the capacitance of the first capacitor may be greater than that of the second capacitor. The second storing means may comprise parasitic capacitances from within the regulation circuit.

An RFID transponder may comprise a regulation circuit as described above. In a preferred embodiment such RFID transponder additionally comprises modulation means wherein such modulation means modulates the reference or reference voltage.

According to a fourth aspect of the present invention there is provided a method of regulating a voltage comprising the steps of: providing an input voltage at an input; rectifying the input voltage with a first rectifier coupled to the input to produce a first output voltage from an output of a first rectifier; rectifying the input voltage with a second rectifier coupled to the input to produce a second output voltage from an output of a second rectifier; comparing the second output voltage with a reference voltage to produce a difference voltage; and adjusting the first output voltage, based on the difference voltage. A regulation circuit according to the invention may be used, for example, in any RFDD transponder, or any other application where voltage regulation with an improved response time is desirable. The supply voltage from the first arm of the circuit may be used to supply the device or application with power for its operation. In apparatus using a regulation circuit according to the present invention the derived power may be used to power all or part of the apparatus receiving the supply voltage.

In this description, the term RFID transponder should be taken to include an RFID tag, an NFC device or apparatus in target mode or any similar device or apparatus which is responsive to receipt of an externally generated RF field. Such an RFID transponder may be stand-alone or comprised within a larger device, for example a portable communications device, poster, advertising board, games console. Where comprised within a larger device the RFID transponder functionality may be on one or several separate integrated circuits or alternatively comprised within the functionality (either in whole or in part) of the larger device. In any regulation circuit using the incoming RF field or signal as a power source, such power source can be represented by a signal source with an internal impedance. The internal impedance may comprise resistors, inductors, capacitors, coupling between inductors, coupling between antennas, any combination or any other impedance apparatus known to persons skilled in the art. Such a signal source with internal impedance shall be referred to below as the input signal.

In this description the term shunt device may mean one shunt device or a combination of several shunt devices. Such shunt device may be any electrically controllable switch or electrically controllable device with variable electrical characteristics, for example a field effect transistor (FET).

Brief description of the drawings

Figure 1 is a circuit diagram that shows a preferred embodiment of a voltage regulator; Figure 2 is a circuit diagram that shows the preferred embodiment of the voltage regulator of Figure 1, incorporated within an RFID transponder; and

Figure 3 a and Figure 3b are graphs that show input and output waveforms for the voltage regulator of Figure 2 respectively.

Detailed Description of the Invention

Figure 1 shows an example of a regulation circuit according to a preferred embodiment of the present invention.

The circuit of Figure 1 is supplied with a signal source 223 comprising an AC power source 200 which outputs a variable unregulated voltage and an internal impedance 202. The signal source 223 supplies an input signal 201 across two nodes 218 and 219. The circuit has two arms: the first arm comprises a bridge rectifier 213 to 216 and an energy-storage capacitor 217. The first arm of the circuit outputs an output voltage 205 across two nodes 203 and 204. A load 212 is connected across the nodes 203 and 204. The load 212 comprises a device or apparatus requiring a regulated DC voltage. The second arm of the circuit has a common input to the first arm of the circuit, and comprises two diodes 800 and 801, forming a second or auxiliary rectifier. A signal 803 is produced at the output of the auxiliary rectifier. The output of the auxiliary rectifier is connected to a capacitor 802. A potential divider formed from two resistors 220, 221 with a node 222 between the resistors is also connected to the output of the auxiliary rectifier, in parallel to the capacitor 802. The node 222 of the potential divider is connected to an amplifier 209, and the output of the amplifier is coupled to a shunt device comprising first and second field effect transistors (FET) 210 and 211. The voltage at node 222 is fed into a positive (or non-inverting) input of an amplifier 209, and compared with a reference voltage Vref 207. Vref can be produced by a Zener Diode, for example. If the circuit is an integrated circuit then Vref will for example be produced from a band gap voltage reference providing a stable reference at about 1.25 V. Thus, the second arm of the circuit takes from the input of the bridge rectifier (via diodes 800 and 801) a "measurement" voltage signal 803 which is input to the amplifier 209 via the voltage divider resistors 220 and 221. The values of resistors 220 and 221 are chosen such that when the circuit is stable the voltage at node 222 is substantially equal to the reference voltage Vref 207. The operation of the FETs 210 and 211 depends upon the polarity of the input signal 201. The operation of the diodes in the first arm of the circuit and the operation of the shunt device will now be described: When the input signal 201 is hi the positive half cycle of the AC waveform, and the node 218 is more positive than the node 219, current flows through the impedance 202, then through the diode 213 and the load 212. Such current returns to the source 200 through the diode 216. This means that the node 203 is made more positive than the node 204. During positive half cycles, if the shunt current is controlled to pass through the first FET 210, the shunt current returns to the source 200 through the second FET 211, the diode 216 or a combination of both. m operation, when the input signal 201 is in the negative half cycle of the AC waveform, and the node 218 is more negative than the node 219, current flows in the opposite direction, and the operation of the first and second FETs 210 and 211 is interchanged. In this case, the diode 214 conducts instead of the diode 213, and the diode 215 conducts instead of the diode 216. This makes the node 203 more positive than the node 204, as above. In each half cycle of the input signal the energy-storage capacitor 217 is charged.

In the second arm of the circuit the signal 803 passes through the diode 800 when the input signal 201 is in the positive half cycle of its waveform, where the node 218 is more positive than the node 219. The signal 803 is supplied from the diode 801 when the input signal 201 is in the negative half cycle of its waveform, where the node 219 is more positive than the node 218. Only two diodes 800 and 801 are required to form the second rectifier in the second arm of the circuit because a return path is provided by two of the diodes 215 and 216 in the main bridge rectifier.

The capacitor 802 in the second arm of the circuit has the effect of 'smoothing' the sample signal 803 which is fed into the amplifier 209, via the voltage divider made up from resistors 220 and 221, so that it represents the supply voltage 205 output to the load 212. However, the capacitor 802 is arranged to have a much smaller capacitance than that of the energy storage capacitor 217 in the first arm of the circuit. In one example the capacitance of capacitor 217 is larger than the capacitance of capacitor 802 by at least the ratio 25:1, in a preferred embodiment such ratio is at least 50:1 and in a most preferred embodiment such ratio is at least 100:1.

This means, for example, that the second arm of the circuit has a much faster response to variation in the input signal than the first arm of the circuit. Since both capacitors 802 and 217 charge through the same input impedance 202, the charging time constant (which is given by RC) of the capacitor 802 in the second arm of the circuit is smaller than the charging time constant of the energy-storage capacitor 217 in the first arm of the circuit. Accordingly, the capacitor 802 will charge faster than the energy-storage capacitor 217 when the amplitude of the input signal increases, and therefore the shunt can be triggered more quickly than in the prior art circuits to prevent a voltage surge to the load 212.

The capacitor 217 discharges through the load 212, whereas the capacitor 802 discharges through the resistors 220 and 221. The value of the sum of resistors 220 and 221 is roughly equal to the load resistance 212 and because of this and because capacitor 802 is much smaller than capacitor 217, the discharge time constant of the second arm is very much less than that of the first arm. Accordingly, the capacitor 802 will discharge faster than the energy- storage capacitor 217 when the amplitude of the input signal decreases, and therefore the shunting effect can be reduced more quickly than in the prior art circuits. The faster charging and discharging of capacitor 802 facilitates a more stable regulation circuit than those in the prior artThe capacitor 802 could be disposed at the input of the amplifier 209, and/or be built into the amplifier 209, and/or be disposed at the input of the shunt devices 210 and 211. The capacitor 802 may be present in the circuit as a separate component, or it may be made up of parasitic capacitances present in the other components of the circuit.

In an alternative embodiment (not shown in Figures 1 or 2) the capacitor 802 can be omitted. In this case the measurement voltage 803 mirrors the input signal 201 to the circuit including the intensity variations seen in the input signal. In this example, such a mirrored signal will be a full-wave rectified dc- version of the ac input signal. In this case changes in the amplitude of the input signal are monitored without the smoothing effect of a capacitor. In such cases the circuit design will have to take into account the changed nature of the relationship between a non-smoothed measurement signal and the smooth Vref in order to provide the desired regulated output voltage.

An example of the approximate values of the components in the circuits is as follows: the capacitor 802 has a capacitance of IpF; the capacitor 217 has a capacitance of 10OpF; the load 212 has a resistance of 70kΩ ; and the resistors 220 and 221 have a total resistance of 50kΩ . Such values are given for example only and it should be clear to the skilled man that such can be varied depending on the regulation circuit and use for such application circuit. Figure 2 shows the regulation circuit of Figure 1 used in a transponder according to a preferred embodiment of the present invention. As shown, the transponder is in communication with an RFE) transceiver 400. Such an RFID transceiver transmits an RF field which is received by the RFDD transponder at antenna 500. The transponder can derive energy from incident magnetic field, and, further, can extract data and/or information from any incident field from the transceiver, for example. In the discussion of Figure 2 the blocks, signals and components 206, 208 to 211, 213 to 217, 220 to 222, and 800 to 803 carry out the same functions as the correspondingly numbered blocks, components and signals of Figure 1.

The antenna 500 in this example is a coil inductor and an AC voltage is induced across it when a magnetic field 405 is present; this magnetic field would usually be produced by an RFID transceiver, hi this example a capacitor 501 is connected in parallel across the antenna 500, forming a tuned circuit together with the antenna 500. Such a tuned circuit tends to maximize the induced voltage across the antenna 500. In most cases the antenna 500 can also take the place of the impedance 202 in Figure 1 since the source impedance of antenna 500 is sufficiently high. The source impedance depends upon the mutual coupling between transceiver and transponder and the impedance of antenna 500 at its operating frequency. Whilst the circuit of Figure 2 uses an induction antenna, other coupling/transmission methods are possible, such as, for example, the use of electric field antennas and one example is a dipole antenna.

In addition to the regulation circuit described in Figure 1, the RFID transponder comprises a demodulator means 702 connected across the antenna, and a modulator means 703. The demodulator means 702 and the modulator means 703 are both in communication with a control means 704. The transponder further comprises a data store, memory or database 705 in communication with the control means 704. In preferred embodiments, a voltage adder 706 is also provided; an output of the modulator means 703 is input into the voltage adder 706, together with a reference voltage Vref from a voltage generation means 700. In operation, an incident electromagnetic signal 405, such as a signal sent from an RFID transceiver 400, for example, is received and demodulated by the demodulator means 702, so that data and/or instructions can be extracted from the signal. Once the demodulator means 702 has demodulated the signal it sends the demodulated signal to the control means 704, so that any extracted data and/or instructions from the signal can be processed. The control means 704 acts upon information from the demodulated signal by accessing the data store 705, and processes the information/data depending on the content of the incident signal and/or a predetermined internal process of the transponder. Data from the signal may be stored in the data store 705 and/or data pre-stored in the data store 705 may be retrieved. This retrieved data can then be sent to the modulation means 703 for transmission to a transceiver.

The operation of the voltage adder 706 and the amplifier 209 will now be described. The voltage adder is a preferred feature which need not be present in all circuits of the invention. The voltage adder 706 is supplied with a modulated voltage output 701 from the modulation means, and is also supplied with a reference voltage Vref. A voltage signal 707 is output from the voltage adder, and input into the inverting input of the capacitor 217. When no modulated voltage signal 701 is fed to the voltage adder 706, the amplifier 209 receives only the voltage Vref and so operates to perform the voltage regulation as described for Figure 1.

However, when the modulation means 703 provides a modulated signal 701 to the voltage adder 706, the amplifier 209 receives a voltage 707 equal to Vref added to the modulated signal 701. The amplifier 209 compares the voltage 222 from the potential divider in the second arm of the circuit to the voltage 707 as before; and the modulated signal 701 causes small changes to the voltage output from the amplifier, which follow the pattern of modulated data from the modulation means 703. As described above, changes in the voltage output from the amplifier 209 change the conductivity of the FETs 210 and 211, and therefore cause directly related small changes in the current drawn from the antenna 500. The small changes in current modulate the impedance across the antenna according to the signal from the modulation means 703. This impedance modulation couples back to the transceiver generating the field 405, and is demodulated by the transceiver. Hence, the RFID transponder can send information about its location, identity, or information about a product associated with the RFID transponder, to the RFDD transceiver.

According to Figure 2 the amplifier 209 receives its reference voltage 707 from the voltage adder 706. The transponder functionality of Figure 2 is able to carry out signaling to a transceiver at high data rates by using output voltage modulation. The faster charging and discharging of capacitor 802 as described for Figure 1 facilitates a faster modulation data rate than the data rate achievable in the prior art shunt regulators.

Specifically, the operation of the transponder is as follows: the demodulator means 702 sends a demodulated signal to the control means 704, and the control means 704 acts upon information within the demodulated signal. According to an internal routine the control means 704 may store or retrieve data from the data store 705 and/or may send data to the modulation means 703.

When the modulation means 703 is not providing a modulated voltage signal 701 to the voltage adder 706, the amplifier 209 receives voltage Vref and so operates to perform the voltage regulation as described for Figure 1. However, when the modulation means 703 provides a modulated signal 701 to the voltage adder 706, the amplifier 209 receives a voltage equal to Vref added to the modulated signal 701, and operates to perform the voltage regulation as before but with small changes to the regulated voltage; these small changes follow the pattern of modulated data from the modulation means 703, and cause directly related small changes in the current drawn from the antenna 500. The small changes in current have the effect that the impedance across the antenna is modulated by the signal from the modulation means 703. This impedance modulation is coupled to the transceiver generating the field 405, and is demodulated by the transceiver. An example of a 100% modulated signal sent by a transceiver is shown in Figure 3 a. A modulation in the waveform is shown as a gap 604 in an RF signal 600, where there is a drop in the intensity of the signal. The DC output voltage waveform shown as 601 in Figure 3b (node 206 in Figure 2) has to be maintained at a substantially constant level such that the gap, shown occurring at a period 603, does not affect the correct operation of the transponder. To achieve this the energy-storage capacitor 217 is of high capacitance, so that more energy can be stored which can be used by the circuit during the drop in intensity of incident radiation of the modulated RF signal 600 in Figure 3 a and shown as 405 in Figure 2.

Although the foregoing examples discuss the use of FETs (field effect transistors), it will be apparent that any other transistor type such as bipolar transistors, or any other known switching means or controllable device can be used to provide similar effect.

It will be apparent that diodes in the foregoing discussion could be constructed from any of the known methods, such as for example FETs used as a rectifier, or the type known as PN diodes.

Wherever a rectifier is shown as a full-wave rectifier, it will be apparent that other rectification methods could be used individually or in any combination. Other rectifying methods may involve half-wave rectifiers or other rectification means such as voltage multipliers. An apparatus using a regulator according to the present invention need not comprise all the functionality of a transponder. An apparatus using a regulator according to the present invention may also be in standalone form (either hand held or free standing) or disposed within a larger device or host device/ system, for example a mobile communications device, a PDA, a personal computer, a laptop, a game console, a vending machine, a digital music player etc. Such apparatus or devices may comprise an integrated circuit or alternatively the functions of the apparatus may be performed by separate component parts or separate integrated circuits. Where a regulator is provided within a larger device the functions may be shared between the transponder and the larger device, for example the transponder may not have a memory but may use a memory means provided within the larger device. It will be apparent that other systems, devices and methods can be advantageously designed to use the present invention.

An apparatus using a regulator according to the present invention may communicate with a transceiver. Such a transceiver can be in standalone form (either hand held or free standing) or disposed within a larger device, host device or system, for example a mobile or fixed communications device or system, computer, ticket inspection machine, transport access mechanism or gate etc.

It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

In a yet further independent aspect of the invention there is provided a regulation circuit including: a first rectifier with an input, the first rectifier adapted to receive an input signal and provide a first rectified output signal on a first output, a second rectifier with an input coupled to the input of the first rectifier, the second rectifier adapted to receive an input signal and provide a second rectified output signal on a second output, a comparator coupled to the second output and a reference, the comparator adapted to generate a difference signal on an output based on the difference between the reference and the rectified output signal of the second rectifier, and at least one shunt device coupled to the input of the first rectifier for controlling the signal amplitude on the input of the first rectifier, wherein the output of the comparator is coupled to a control input of the shunt device such that a difference signal on the output of the comparator operates the shunt device to control the amplitude of the signal on the input of the first rectifier.

Claims

1. A regulation circuit comprising: a first rectifier coupled to an input signal, and being arranged to deliver a first output signal; a second rectifier coupled to the input signal, and being arranged to deliver a second output signal; an amplifier coupled to the second output signal and to a reference signal and being arranged to generate a third output signal related to the difference between the reference signal and the second output signal; and a shunt device coupled to the input signal and being controllable via the third output to control a signal amplitude of the input signal.

2. A voltage regulation circuit comprising: a first rectifier coupled to an input signal, and being arranged to deliver a first output voltage; a second rectifier coupled to the input signal, and being arranged to deliver a second output voltage; an amplifier coupled to the second output voltage and to a reference voltage and being arranged to generate a third output voltage related to a voltage difference between the reference voltage and the second output voltage; and a shunt device coupled to the input signal and being controllable via the third output to control a voltage level of the input signal.

3. A circuit according to claim 1 or 2, wherein the circuit further includes: a first storing means for storing energy from the output of the first rectifier.

4. A circuit according to claim 3, wherein the circuit further comprises a second storing means for storing energy from the output of the second rectifier.

5. A circuit according to claim 4, wherein the capacity for storing energy of the first storing means is at least 25 times greater than the capacity for storing energy of the second storing means.

6. A circuit according to claim 4, wherein the capacity for storing energy of the first storing means is at least 50 times greater than the capacity for storing energy of the second storing means.

7. A circuit according to claim 4, wherein the capacity for storing energy of the first storing means is at least 100 times greater than the capacity for storing energy of the second storing means.

8. A circuit according to claim 1, wherein the circuit further includes modulating means for modulating the reference signal.

9. A circuit according to claim 2, wherein the circuit further includes modulating means for modulating the reference voltage.

10. An RFID transponder comprising a regulation circuit of the form set out in any of claims 1 to 9.

11. Near field communication apparatus comprising a regulation circuit of the form set out in any of claims 1 to 9.

12. An electrical device comprising a regulation circuit of the form set out in any of claims 1 to 9.

13. A method of regulating a voltage comprising the steps of: providing an input voltage at an input; rectifying the input voltage with a first rectifier coupled to the input to produce a first output voltage from an output of a first rectifier; rectifying the input voltage with a second rectifier coupled to the input to produce a second output voltage from an output of a second rectifier; comparing the second output voltage with a reference voltage to produce a difference voltage; and adjusting the first output voltage, based on the difference voltage.

14. A method according to claim 13, further including the step of modulating the difference voltage.

15. A regulation circuit comprising: a first arm comprising a first rectifier for rectifying an input signal and delivering a first output signal; a second arm comprising a second rectifier, for rectifying the input signal and delivering a second output signal; an amplifier for generating a difference signal related to a difference between a reference signal and the second output signal; and a shunt device for controlling the input signal based on the difference signal.

16. A regulation circuit according to claim 15, wherein the first arm further comprises a first capacitor.

17. A regulation circuit according to claim 16, wherein and the second arm further comprises a second capacitor.

18. A regulation circuit according to claim 17, wherein a charging or discharging time constant associated with the first capacitor is at least 25 times greater than the charging or discharging time constant associated with the second capacitor.