GB2579588A

GB2579588A - Power electronics for use in smart cards and other applications

Info

Publication number: GB2579588A
Application number: GB1819803.6A
Authority: GB
Inventors: Diaz Victor; Freitas Vitor; Litwinow Sebastian; Lloyd Alison
Original assignee: Drayson Technologies Europe Ltd
Current assignee: Freevolt Technologies Ltd
Priority date: 2018-12-04
Filing date: 2018-12-04
Publication date: 2020-07-01
Anticipated expiration: 2038-12-04
Also published as: GB2579588B; WO2020115483A1; GB201819803D0; EP3891660A1

Abstract

The invention provides mounting systems, such as systems used to connect near field RF communications chips into near field RF communications enabled apparatus. The system typically comprises a chip coupling, an auxiliary power provider, and an antenna coupling. The systems may further include a splitter 1002 for splitting an alternating electrical signal, received at a first port, between a second and third port. The second port and third port may be connected together by a frequency selective connection, so that the degree of isolation between the two ports is frequency selective the isolation may be better at low frequencies (such as DC) than at higher frequencies (such as RF). The aim of the invention is to divide the harvested power from an interrogator field so as to provide power to an auxiliary circuit 1006 (for example a fingerprint sensor) in a smartcard 1000. Splitters and rectifiers 1004 are used which comprise capacitors, inductances and resistors arranged in various ways to achieve the required impedance matching and stabilisation.

Description

Power Electronics for use in Smart Cards and Other Applications

Field of Invention

The present invention relates to methods and apparatus, and more particularly to methods and apparatus for auxiliary power harvesting in near field radio frequency (RF) cormunications enabled systems, such as systems comprising near field RF communications functionality provided by an integrated circuit.

Background

Smart cards, also known as chip cards, or integrated circuit cards (ICC), are increasingly prevalent. A wide variety of such pocket-sized cards with embedded integrated circuits are in use in a wide variety of applications. The most frequent uses of such cards relate to financial transactions, mass transit systems, and access control. Smart cards are made of plastic, generally polyvinyl chloride, but sometimes polyethylene-terephthalatebased polyesters, acrylonitrile butadiene styrene or polycarbonate. Reusable smart cards may also be made from paper.

Such cards often incorporate an integrated circuit, IC, and some source of power such as an near field RF communications interface for powering the IC and providing data communications to and from it.

An IC device, herein called a chip, traditionally consists of a single semiconducIor die which has a particular EuncTion and which is adapted to interact with other chips and components. For example, a traditional chip might be a microprocessor, a memory controller, or a memory array. IC systems may include two or more chips, as well as other electronic and electrical components, each attached to and interconnected through a mounting system such as a printed circuit board.

Near field RF (radio frequency) communication requires an antenna of one near field RF communicator to be present within the alternating magnetic field (H field) generated by the antenna of 5 another near field RF communicator by transmission of an RF signal (for example a 13.56 Mega Hertz signal) to enable the magnetic field (H field) of the RF signal to be inductively coupled between the communicators. The RF signal may be modulated to enable communication of control and/or other data. Ranges of 10 up to several centimetres (generally a maximum of 1 metre) are common for near field RF communicators.

Near field communication in the context of this application may be referred to as near-field RF communication, near field RFID (Radio Frequency Identification) or near field communication. The range of such devices depends on the antenna used but may be, for example, up to 1 metre.

Communication of data between NFC communicators may be via an active communication mode in which the NFC communicator transmits or generates an alternating magnetic field modulated with the data to be communicated and the receiving NFC communicator responds by transmitting or generating its own modulated magnetic field, or via a passive communication mode in which one NFC communicator transmits or generates an alternating magnetic field and maintains that field and the responding NFC communicator modulates the magnetic field to which it is inductively coupled with the data to be communicated, for example by modulating the load on the inductive coupling ("load modulation"). Near field RF communicators may be actively powered, that is have an internal or associated power source, or passively powered, that is derive a power supply from a received magnetic field. Generally an RF transceiver will be actively powered while an RF transponder may be passively or actively powered.

Examples of near field RF communicators are defined in various standards for example ISO/IEC 18092 and ISO/IEC 21481 for NFC communicators, and ISO/IEC 14443 and ISO/TEC 15693 for near field 5 RF communicators.

The ability of near field RF communications devices to be passively powered is a significant benefit. Some near field communicator chips also provide auxiliary power outputs. This can enable power harvested by the near field RF communicator to be used by other circuits.

UK patent application GB2531378 describes an RFID system in which when an RFID reader sends a command to an RFID device, the device does not respond, but rather waits and harvests the power to drive some auxiliary functionality e.g. functionality not required for responding to the command, for example the command may be a "request to provide identification code" command. In this prior art system, a response to the command from the RFID device is intentionally delayed so as to allow the auxiliary function to be performed first. In this system, the auxiliary function is biometric authentication, and the RFID device does not respond to the command until the biometric authentication has been completed.

This may extend the interaction time of the RFID device (e.g. the period of time for which an RFID device must be held in proximity to a reader). The perceived delay in operation associated with this may be unacceptable to users.

Summary

Aspects and examples of the present invention are set out in the appended claims.

In an aspect there is provided a mounting system for a near field RF communications chip, the system comprising: a substrate for carrying electronic components, and for providing electrical interconnections therebetween; a chip coupling carried by the substrate for connecting a near field RF communications chip to the mounting system; an auxiliary power provider, separate from said near field RF communications chip, and adapted for providing electrical power output based on a received alternating electrical signal; and, an antenna coupling for connecting a near field RF communications antenna to said mounting system; and a splitter, for splitting alternating electrical signals, the splitter comprising: a first port connected to the antenna coupling and having a first input impedance; a second port connected to the first port and configured to provide a first part of the alternating electrical signal to the auxiliary power provider; and a third port connected to the first port and configured to provide a second part of the alternating electrical signal to the chip coupling; wherein the splitter is configured to maintain the first input impedance so that: the output impedance of the second port is maintained in the event of fluctuations in the output impedance of the third port; and the output impedance of the third port is maintained in the event of fluctuations in the output impedance of the second port.

The second port may comprises a first terminal and a second terminal, and the third port comprises a first terminal and a second terminal, and the second port's first terminal and the -5 -third port's first terminal are each connected to a common point by a reactive impedance, such as an inductor or capacitor.

The common point may be connected to a first terminal of the 5 first port. The second port's first terminal may be connected to the third port's first terminal by a series connection of two inductors to provide RF isolation between the two first teLminals. An intermediate part of the series connection of the two inductors may be connected to a reference voltage such as 10 ground, for example wherein the second port's second terminal is connected to the third port's second terminal by a series connection of two capacitors.

A first one of the two capacitors may connect the intermediate part of the series connection of the two inductors to the second port's second terminal. A second one of the two capacitors may connect the intermediate part of the series connection of the two inductors to the third port's second terminal.

The first input impedance may be matched to the output impedance of said near field RF communications antenna, and the output impedance of the second port is selected to match the input impedance of the near field RF communications chip. It will be appreciated in the context of the present disclosure that this may comprise the output impedance of the second port being matched to the combined input impedance of the antenna and an intermediate matching network, interposed between the second port and the antenna.

The splitter may be configured to provide, at the first port, variations in electrical load corresponding to the variations in electrical load at the third port. The splitter may be configured so that the first part of the alternating electrical signal comprises more power than the second part of the alternating electrical signal.

The splitter may comprise a network of lumped components, such as 5 a Wilkinson divider.

An aspect provides a near field RF communications apparatus comprising: a near field RF communicator; an antenna for coupling with an alternating H-field; an auxiliary rectifier, separate from the near field RF communicator a splitter comprising a network of lumped components, wherein the network is connected to receive an alternating electrical signal from the antenna, and to provide a first part of the alternating electrical signal to the auxiliary rectifier and to provide a second part of the alternating electrical signal to the near field RF communicator.

The splitter may comprise: a first port connected to the antenna and having a first input impedance; a second port connected, by the network, to the first port and connected to the auxiliary rectifier; and a third port connected, by the network, to the first port and to the near field RF communicator.

The second port may comprise a first terminal and a second terminal, and the third port comprises a first terminal and a 30 second terminal, and the second port's first terminal is at least partially isolated from the third port's first terminal. The second port's first terminal may be connected to the third port's first terminal by a series connection of two ground isolation inductors to provide RF isolation between the two first terminals.

The splitter may be configured so that: the output impedance of the second port is maintained in the event of fluctuations in the output impedance of the third port; and the output impedance of the third port is maintained in the event of fluctuations in the output impedance of the second port.

The first input impedance may be matched to the output impedance of the antenna, and the second port may have an output impedance selected to match the input impedance of the near field RF communicator. It will be appreciated in the context of the present disclosure that this may comprise the output impedance of the second port being matched to the combined input impedance of the near field RF communicator and an intermediate matching network, interposed between the second port and the near field RF communicator.

The near field RF communicator may be provided by an integrated circuit, such as a chip, that is separate from the splitter.

An aspect provides a power splitter for a near field RF 25 communications apparatus, the power splitter comprising: a first port for receiving an alternating electrical signal from a near field communications antenna; a second port connected to the first port and configured to provide a first part of the alternating electrical signal to a 30 rectifier of an auxiliary power provider; a third port connected to the first port and configured to provide a second part of the alternating electrical signal to a near field RF communicator to enable the near field RF communicator to communicate via the near field communications antenna; a network of lumped components configured to connect the first port to the second port and the third port, and to provide: an input impedance at the first port which matches the output impedance of the antenna at the first port; an output impedance at the second port which matches the input impedance of the rectifier; and an output impedance at the third port which matches the input impedance of the near field RF communicator. It will be appreciated in the context of the present disclosure that this may comprise the output impedance of the third port being matched to the combined input impedance of the near field RF communicator and an intermediate matching network, interposed between the third port and the near field RF communicator. It will also be appreciated in the context of the present disclosure that the output impedance of the second port may be matched to the combined input impedance of the rectifier and an intermediate matching network, interposed between the second port and the rectifier.

The network of lumped components may comprise two arms connected to provide a bifurcated electrical conduction path, and each arm having an input stage and an output stage. The input stage and the output stage may each be provided by one or more of the network modules illustrated in Figure 4. These may be configured to operate as a Wilkinson divider which splits alternating electrical signals of a near field RF communications frequency band.

The near field RF communications frequency band may comprise 13.56MHz.

An aspect of the disclosure provides a smart card for carrying a near field RF communications chip, and a near field RF communications antenna, the smart card comprising: an auxiliary rectifier separate from the near field RF 5 communications chip for providing electrical power to auxiliary circuitry; a power splitter comprising a network of lumped capacitors and printed coil inductors, wherein the network is connected to receive an alternating electrical signal from the antenna, and to provide a first part of the alternating electrical signal to the auxiliary rectifier and to provide a second part of the alternating electrical signal to the near field RF communicator.

The splitter may comprise: a first port for connection to the antenna and having a first input impedance; a second port connected, by the network, to the first port and connected to the auxiliary rectifier; and a third port connected, by the network, to the first port for connection to the near field RF communicator chip. The splitter may be configured so that: the output impedance of the second port is maintained in the event of fluctuations in the output impedance of the third port; and the output impedance of the third port is maintained in the event 25 of fluctuations in the output impedance of the second port.

Brief Description of Drawings

Embodiments of the disclosure will now be described in detail with reference to the accompanying drawings, in which: Figure 1 shows a smartcard comprising a near field RF communications apparatus; -10 -Figure 2 shows a schematic diagram of a power splitter for use in near field communications apparatus such as those described with reference to Figure 1; Figure 3 shows another schematic diagram of a power splitter 5 for use in near field communications apparatus such as those described with reference to Figure 1; Figure 4 shows set of schematic diagrams, each of which may be used to provide one or more modules of the power splitters described with reference to Figure 2 and Figure 3; Figure 5 comprises two diagrams -Figure 5A shows a schematic diagram of a single ended implementation of a splitter, and Figure 5B shows a differential implementation of the splitter.

Figure 6 shows a power splitter for use in near field 15 communications apparatus such as those described with reference to Figure 1; and Figure 7 shows another such power splitter.

In the drawings like reference numerals are used to indicate like elements.

Specific Description

Figure 1 illustrates a smartcard 1000 comprising a near field RF 25 communicator 1014 and circuitry 1002, 1004, 1006, 1008, 1010, 1012, according to the present disclosure.

The smartcard 1000 also comprises an inductive coupler 1016, such as a near field RF communications antenna. The circuitry includes an auxiliary rectifier 1004, which is separate from the near field RF communicator 1014, and which provides DC power to the auxiliary circuit 1006. The auxiliary rectifier may also provide DC power to digital functionality of the near field RF communicator 1014.

A splitter 1002 connects both the auxiliary rectifier 1004 and 5 the near field RF communicator 1014 to the inductive coupler 1016.

The components 1002 to 1014 of the smartcard may be carried by a dielectric substrate, which may be flat and sheet-like for incorporation into the smartcard 1000. For example, this substrate may be laminated with (e.g. sandwiched between) other dielectric layers to provide the body of the smartcard 1000. The smartcard 1000 may thus encapsulate the circuitry 1002, 1004, 1006, 1008, 1010, 1012. The smartcard 1000 may also encapsulate the inductive coupler 1016.

The splitter 1002 can be connected to the inductive coupler 1016 for receiving an RF electrical input signal. The splitter is also connected to the near field RF communicator 1014 and to the auxiliary rectifier 1004. The connection between the inductive coupler 1016 and the splitter 1002 may be a differential (e.g. two-terminal) connection for the provision of a differential signal. Likewise, the connection between the splitter 1002 and the auxiliary rectifier 1004, and between the splitter 1002 and the near field RF communications apparatus 1014 may also be a differential connection.

The splitter is configured to provide a first part of the input RF electrical signal to the near field RF communicator 1014, and to provide a second part to the auxiliary rectifier 1004. This functionality may be provided by a network of electrical impedances, such as inductors and capacitors, connected together to divide the incoming signal into two parts. One example of such a network is a Wilkinson divider.

-12 -The auxiliary rectifier 1004 has a differential output comprising two output connections 1010, 1011. These are connected to the auxiliary circuit 1006 for providing rectified DC electrical 5 energy, derived from the second part of the RF electrical input signal. One output 1010 of the auxiliary rectifier 1004 provides a reference voltage, e.g. a ground. This may be connected to a ground conductor' on the substrate of the circuitry to enable other components carried on the substrate to be referenced to 10 that same voltage. For example, the auxiliary circuit 1006 may also be connected to that ground or reference voltage, and that ground or reference voltage may fix a reference for the voltage levels used in digital logic and/or digital communication operations performed by the auxiliary circuit.

A data communications connection 1012 connects a data communications terminal of the near field RF communicator 1014 to a corresponding data communications terminal of the auxiliary circuit 1006.

The inductive coupler 1016 of the apparatus described herein generally comprises an electrical conductor such as a conductive track or wire arranged for coupling inductively with an alternating H-field to provide an alternating electrical signal. Such arrangements may be referred to as an NFC antenna.

Typically, such an antenna comprises a loop having one or more turns. It will be appreciated in the context of the present disclosures that an NFC antenna may have a large inductance, perhaps of 14tH or more. Such antennas may be adapted for coupling with signals in a near field RF frequency band, which generally comprises 13.56MHz. It will be appreciated in the context of the present disclosure that such signal may have a wavelength of approximately 22m.

The near field RF communicator 1014 may comprise an integrated circuit, which may be implemented as a single semiconductor die -13 - (a chip). The near field RF communicator 1014 may comprise a front end, for connection to the antenna 1016. The front end may include things such as a voltage regulator, a dedicated rectifier for the near field RF communicator, or other circuitry for connecting the near field RF communicator to the antenna 1016. The near field RF communicator 1014 may also comprise an RF controller for performing simple data operations such as modulating and demodulating data from signals received via the antenna 1016. The near field RF communicator 1014 may comprise DC digital logic circuits configured to obtain data from and/or provide data to the RF controller. The digital logic may also communicate such data to/from the auxiliary circuit 1006 via the communications connection 1012. This can provide data communications between the RF interface of the near field RF communicator 1014 and the auxiliary circuit. Such communication may enable the auxiliary circuit 1006 to perform functions such as authentication (e.g. by biometric means) and user input/output for a device communicating with the near field RF communicator 1014 via the RF interface.

The auxiliary rectifier 1004 comprises a rectifying element, such as a diode, arranged to convert the alternating electrical signal received from the splitter into a direct current, DC, electrical signal. This DC electrical signal may be used to power the auxiliary circuit. The auxiliary rectifier may also comprise components for matching the input and/or output impedance of the rectifier to the circuits to which it is connected.

The power splitter 1002 may comprise a network of electrical impedances, such as capacitors and inductors, connected together 30 to provide: (a) an input impedance which matches the output impedance of the antenna 1016, and -14 - (b) a bifurcated electrical conduction path which divides an RF electrical signal received from the antenna 1016 into two parts; (c) a first output impedance which matches the input 5 impedance of the near field RF communicator 1014; (d) a second output impedance which matches the input impedance of the auxiliary rectifier 1014.

For example this functionality of the splitter 1002 may be provided by: an antenna matching network for matching the output impedance of the antenna 1016; a chip matching network for matching the input impedance of the near field RF communicator 1014, and a rectifier matching network for matching the input impedance of the auxiliary rectifier 1014. Connections may be provided between the antenna matching network on the one hand, and, on the other hand, the chip matching network and to the rectifier matching network so that the conduction path from the antenna is bifurcated.

For example, the power divider 11 may comprise a bifurcated electrical conduction path, starting at an input leg and splitting into two arms, one via the chip matching network and the other via the rectifier matching network. The two arms may each comprise a complex output impedance to introduce a selected phase shift to an alternating electrical signal. The phase shift introduced by each of the two arms may be equal to that introduced by the other. The two arms may be connected together by a pure real impedance (e.g. by an ohmic resistive Impedance). This connection between the two arms may be provided at the ends of the arms. This is typically the case in an even divider, such as that illustrated in Figure 3. In an even divider the input power is split 50:50 between the two arms. In uneven dividers, this connection between the two arms may be at some inteuuediate position along their length. For example, as illustrated in Figure 2 each arm may comprise a series of stages, or modules, -15 -each introducing a particular phase shift. In this eventuality, the two arms may be connected together by a pure real impedance at the transition between one of these stages and the next. For example, if each arm provides a it phase shift (180°) in two 7/4 (90°) stages, the two arms may be connected together by a pure real impedance at the 7/4 (90°) point after the first stage. If other numbers of stages, and other phase shifts are used, this connection may be positioned differently. Typically, this connection links points of equal phase on the two arms. Figure 4, and Figure 5 each provide examples of this type of splitter. It will be appreciated in the context of the present disclosure that the phase shift associated with either or both of the arms of the splitter may be provided solely by said arm(s) or may be provided in part by a matching network coupled between that arm and its output (the rectifier or the chip, as the case may be).

Operation of an apparatus 1000 such as that described above with reference to Figure 1 will now be described. To initiate operation, a reader device, such as an RFID reader, or an NFC device operating in reader mode, provides a time varying H-field to the antenna, e.g. at a frequency of 13.56 MHz. By coupling with this H-field, the inductive coupler 1016 provides an alternating electrical signal to the splitter 1002. The power divider splits this input signal to provide two output parts. The first part is provided via the rectifier matching network to the rectifier, and the second part is provided to the near field RF communicator via the chip matching network. The near field RF communicator may derive electrical power from the second part of the alternating signal, and may receive data modulated onto the alternating signal by the NFC reader. It may also respond to this data by sending data back to the NFC reader and/or by performing digital data communication with the auxiliary circuit 1006. While the near field RF communicator is communicating with a reader, e.g. using load modulation, the auxiliary rectifier 1004 converts -16 -the second part of the alternating electrical signal to DC electrical energy, e.g. to power the auxiliary circuit 1006. During this period, the rectifier may present a constant load (e.g. a constant impedance at the rectifier port).

Figure 2 shows a schematic diagram of a power splitter for splitting alternating electrical signals. Such a splitter may be used in near field communications apparatus such as those described with reference to Figure 1.

The splitter comprises a first port for connection to the inductive coupler (e.g. via an antenna coupling), and having a first input impedance. The splitter also comprises a second port connected to the first port and configured to provide a first part of the alternating electrical signal to the auxiliary power provider. The splitter also comprises a third port connected to the first port and configured to provide a second part of the alternating electrical signal to the near field RF communicator.

The splitter may be configured to maintain the first input impedance so that: the output impedance of the second port is maintained in the event of fluctuations in the output impedance of the third port; and the output impedance of the third port is maintained in the event of fluctuations in the output impedance of the second port. One way to provide this functionality is described below with reference to Figure 2.

The first port, the second port, and the third port each comprise a first terminal, and a second terminal. The first port's first terminal 1200 is connected to the first port's second terminal 1202 by a first capacitor 1204. The first port's first terminal 1200 is connected to the second port's first terminal 1206 by a first inductor 1208, and to the third port's first terminal 1212 by a second inductor 1210. The first port's second terminal 1202 -17 -is connected to the second port's second terminal 1214 by a third inductor 1216. The first port's second terminal 1202 is connected to the third port's second terminal 1220 by a fourth inductor 1222.

A second capacitor 1218, and a third capacitor 1224 are connected together in series between the second port's second terminal 1214 and the third port's second terminal 1220. The connection between these two capacitors is also connected to the first port's first terminal 1200, and to the connection between the first inductor 1208 and the second inductor 1210. In addition, a resistor 1226 is connected in parallel with the series connection of the second capacitor 1218 and the third capacitor 1224. Thus, the second port's first terminal 1206 and the third port's first terminal are each connected by an inductor to a common point 1228, and that common point 1228 is connected to the first port's first terminal. It can thus be seen that, although the second port's first terminal and the third port's first terminal are not a common point (e.g. they are not, electrically, the same point), they are coupled to each other to some degree by these inductors 1208, 1210. The connection between them however is, to some degree, frequency selective so the isolation between these terminals is greater at higher frequencies than at lower frequencies.

The common point 1228 may also be connected to the second port's second terminal 1214 by the second capacitor 1218 and to the third port's second terminal 1220 by the third capacitor 1224. The second port's first terminal 1206 may be connected to the second port's second terminal 1214 by a fourth capacitor 1230.

The third port's first terminal 1212 may be connected to the third port's second terminal 1220 by a fourth capacitor 1232. Appropriate selection of these components can provide a high degree of input/output impedance matching, and can provide a -18 -degree of independence between the different ports. For example, it may enable the output impedance of the second port to be maintained in the event of fluctuations in the output impedance of the third port. Likewise, it may permit the output impedance of the third port to be maintained in the event of fluctuations in the output impedance of the second port. It may also serve to decouple the two output terminals 1206, 1212 from each other. This can be of particular utility in systems such as that illustrated in Figure 1. For example, where the second port 1206, 1214 of the splitter is used to provide a first part of the an alternating electrical signal (such as an RF signal received at the first port) to an auxiliary power provider such as a rectifier, and that rectifier is then used to communicate with a digital logic (DC) component of a near field RF communicator connected to the third port.

Figure 3 shows a schematic diagram of a further power splitter circuit for splitting alternating electrical signals. This circuit may provide a fully differential implementation of a splitter for splitting such signals. As illustrated the circuit in Figure 3 comprises a first port 1200, 1202, a second port 1206, 1214, and a third port 1212, 1220.

The splitter shown in Figure 3 has an input leg 20 for connection to an inductive coupler such as a near field RF antenna. The input leg 20 is connected by a bifurcated electrical conduction path to two output arms 22, 24. The first output arm 22 comprises an input stage 22-1 and an output stage 22-2, which are connected together in series. Likewise, the second output arm 24 also comprises an input stage 24-1 and an output stage 24-2.

The input stage 22-1 of the first arm 22 is connected between the input leg 20 and the output stage 22-2 of the first arm 22. The input stage 24-1 of the second arm 24 is connected between the -19 -input leg 20 and the output stage 24-2 of the second arm 24. The connection between the input stage and the output stage of the first arm 22 may be connected, e.g. by a pure real impedance (such as the two resistors R1 and R2) to the connection between the input stage 24-1 and the output stage 24-2 of the second arm 24. The input stages and output stages of the two arms 22, 24 may each comprise networks of passive, reactive, components such as inductors and capacitors The first arm 22 connects the first port 1200, 1202 to the second port 1206, 1214.

In this first arm 22, a first capacitor 2204 is connected between the first terminal 1200 of the first port and the second terminal of the first port 1202. A first plate of the first capacitor 2204 is connected by a first inductor 2210 to a first plate of a second capacitor 2206. The second plate of the first capacitor 2204 is connected by a second inductor 2212 to a second plate of the second capacitor 2206. In addition the second plate of the second capacitor 2206 is also connected by a third inductor 2214 to the second port's second terminal 1206. The first plate of the second capacitor 2206 is connected to the second port's first terminal 1214 by a fourth inductor 2216. The terminals 1206, 1214 of the second port may be connected together by a third capacitor 2218. The arrangement described above provides one of two bifurcating arms, which split the incoming RF electrical signal received at the port 1200, 1202, into two parts each of which can be conducted along a respective corresponding one of the two arms.

The second arm 24 comprises the same arrangement of inductors and capacitors 2204', 2206', 2210', 2212', 2214', 2216', 2218' as the first arm. Its topology may thus be identical to that of the first arm, but instead of connecting the first port to the second -20 -port 1206, 1214, the second arm connects the first port 1200, 1202 to the third port 1212, 1220.

To connect a mid-point of the two arms 22, 24 together, the first 5 port's first terminal 1200 is connected to a first resistor R1 by the second inductor 2212. The first resistor R1 also connects the second inductor 2212 to the third inductor 2214'. The first resistor R1 is thus connected to the third port's second terminal 1220 by the second arm's third inductor 2214'.1n addition, the first port's second terminal 1202 is connected to a second resistor R2 by the second arm's first inductor 2210'. The second resistor R2 also connects the second arm's first inductor 2210' to the first arm's fourth inductor 2216. The first resistor R2 is thus connected to the first port's first terminal 1214 by the first arm's fourth inductor 2216.

Although, as illustrated in Figure 3, the topology of the two arms 22, 24 may be the same, of course the component values may be different.

The network 2204, 2206, 2210, 2212, provides the input stage 22-1 of the first arm 22. Likewise, the network 2206, 2214, 2216, 2218 provides the output stage of the second arm. The network 2204', 2206', 2210', 2212', provides the input stage 24-1 of the second arm 24. Likewise, the network 2206', 2214', 2216', 2218' provides the output stage 24-2 of the second arm 24.

Each of these stages 22-1, 22-2, 24-1, 24-2 may be provided by any one of the networks illustrated in Figure 4. In general, any 30 such network may only comprise either: * modules identified in that drawing as "high pass filter networks" (namely modules 4A, 4B, 4C, 4D, 4E, and 4F); or * modules identified in that drawing as "low pass filter networks" (namely modules 4G, 4H, 41, 4J, 4K, and 4L) -21 -It will be appreciated in the context of the present disclosure that, although the diagram of Figure 4 illustrates these modules as separate elements each comprising a discrete number of components, where two such modules are connected together the resultant circuit may comprise parallel connections of capacitors, and series connections of inductors, which may behave substantially as a single capacitor or inductor respectively. For example, it can be seen that the first arm 22 of the splitter illustrated in Figure 3 may comprise two of the high pass filter modules 4E connected in series to provide the two stages 22-1, 22-1 of the arm 22. However the capacitor 2206 corresponds to what might alternatively be provided by two separate capacitors in parallel -but it can be electrically equivalent to provide a single capacitor instead as shown in Figure 3 where the capacitors 2206, 2206' play a role in both the input stage 22-1, 24-1 and the output stage 22-2, 24-2 of the relevant arm 22, 24.

Figure 5 is a functional block diagram or another example of a 20 splitter 902 such as that described above with reference to Figure 2 and Figure 3.

The splitter shown in Figure 5 has an input leg for connection to an antenna. The input leg 20 is connected by a bifurcated electrical conduction path to two output arms 22, 24. The first output arm 22 comprises an input stage 22-1 and an output stage 22-2, which are connected together in series. Likewise, the second output arm 24 also comprises an input stage 24-1 and an output stage 24-2.

The input stage 22-1 of the first arm 22 is connected between the input leg 20 and the output stage 22-2 of the first arm 22. The input stage 24-1 of the second arm 24 is connected between the input leg 20 and the output stage 24-2 of the second arm 24. The -22 -connection between the input stage and the output stage of the first arm 22 may be connected, e.g. by a resistor (not shown) or other pure real impedance, to the connection between the input stage 24-1 and the output stage 24-2 of the second arm 24.

The input stages and output stages of the two arms 22, 24 may each comprise networks of passive, reactive, components such as inductors and capacitors arranged to provide a phase shift to the input signal. These may be lumped components. The phase shift provided by the input stage 22-1, 24-1 of each arm 22, 24 may be equal to that provided by the input stage of the other arm 24, 22. Also, the phase shift provided by the output stage of each arm may be equal to that provided by the output stage of the other arm. These stages may be arranged as either high pass filters, or low pass filters. Significantly, the use of such structures may reduce changes in the output impedance of one arm due to changes in the load/impedance presented at the output of the other arm. By selecting the impedance of these different stages appropriately, the power of the alternating electrical signal received from the input leg may be divided between the two arms according to a selected ratio, R. The division of power between the first arm and the second arm may be controlled by selecting the ratio of the impedance of the input stage of the each arm relative to the output stage of that arm, and by selecting the ratio of the impedance of the input stage of the first arm to the impedance of input stage of the second arm. For example, a ratio of power division, R, may be provided between a 'main branch' arm which takes more of the power from the input leg than a 'secondary branch' arm. To achieve this, the magnitude of the impedance of the input stage of the 'main branch' arm may be L/R of the impedance of the input stage of the 'secondary branch' arm. The 'main branch' arm output stage may have an impedance equal to the 'main branch' arm input -23 -stage divided by the square root of (1+R). The 'secondary branch' output stage may have an impedance equal to the 'main branch' arm input stage divided by the square root of (R*(1+R)).

The splitter 902 shown in Figure 5A is illustrated as being single ended, but it will be appreciated in the context of the present disclosure that differential embodiments may also be provided. Figure 5B provides a diagram of such an arrangement. And it can be seen that this defines a class of splitters to which the splitter illustrated in Figure 3 belongs. In such differential embodiments either the modules 4E and 4F are used, or the modules 4K and 4h are used (dependent on whether a high pass filter or low pass filter implementation is desired.

Figure 6 shows a power splitter such as that described above. Unlike some of those power splitters however, the splitter illustrated in Figure 6 may provide an even 50:50 split of input power.

The splitter 904 in Figure 6 comprises an antenna coupling 30, a rectifier coupling 34, a communicator coupling 32. It also comprises an input leg 36 and two arms 38, 40, each providing an electrical conduction path for an alternating electrical signal. The input leg 36 joins the antenna coupling 30 to a junction with the two arms 38, 40. At the junction the conduction path provided by the input leg 30 bifurcates into two conduction paths provided by the two arms 38, 40. The first arm 40 joins the junction to the rectifier coupling 34 for connection to a rectifier. The second arm 38 joins the junction to the communicator coupling 32, e.g. for connection to a near field RF communicator such as a chip.

The first arm 40 comprises a first capacitor 42 connected between the junction and a reference voltage connection such as ground.

-24 -It also comprises a first inductor 44 connected between the junction and a second capacitor 46. The second capacitor 46 is connected in series between the first inductor 44 and the reference voltage connection. The connection between the first inductor 44 and the second capacitor 46 is also connected to the rectifier coupling 34. The complex impedance of the first arm 40 may be selected to introduce a phase shift, such as 90°, into an alternating signal of the near field communications frequency band.

The second arm 38 comprises a third capacitor 48 connected between the junction and the reference voltage connection. It also comprises a second inductor 50 connected between the junction and a fourth capacitor 52. The fourth capacitor 52 is connected in series with the second inductor 50 and the junction, and between the second inductor 50 and the reference voltage connection. The connection between the second inductor 50 and the fourth capacitor 52 is connected to the communicator coupling 32. The rectifier coupling 34 is connected to the chip coupling 32 by a resistor 54. The complex impedance of the second arm 38 may be selected to introduce a phase shift, such as 90°, into an alternating signal of the near field communications frequency band.

The first arm 40 and the second arm 38 may each have a complex output impedance, for example they may each introduce a phase shift to the alternating electrical signal. The first arm and the second arm may be configured to introduce an identical phase shift. For example each may be configured to introduce a 90° phase shift.

In terms of the division of power between the two arms, the split provided by such an arrangement may be even. The magnitude of the combined impedance provided by the first arm and the second arm -25 -together at the junction may be equal to the magnitude of the output impedance of the input leg. For example, in an even splitter such as that illustrated in Figure 5, each arm may have an input impedance equal to twice the magnitude of the output impedance of the input leg. In an even splitter the magnitude of the complex impedance of the first arm may be equal to that of the second arm.

In the system shown in Figure 6, the first capacitor 42, the 10 second capacitor 46, the third capacitor 48 and the fourth capacitor 52 may all have the same capacitance. This capacitance may be on the order of pico-farad, e.g. between 1*10-13F and 1*10-F. The first inductor 44 and the second inductor 50 may also have the same inductance, and this may be on the order of nano-15 henry, e.g. between 1*10-x1H and 1*10-51-1. The resistor which connects the rectifier coupling to the chip coupling may have a resistance equal to twice that of the real part of the antenna impedance and/or twice that of the real part of the output impedance of the input leg.

Any combination of capacitors placed in parallel may be combined into a single capacitor with a value that may be the addition of the capacitance of each single capacitor (for example capacitor 42 and 48) Figure 7 shows another power splitter 906 such as those described above with reference to Figure 2 and Figure 3. Figure 7 is one example of an uneven splitter.

In an uneven splitter, configured to provide more power to the auxiliary rectifier than to the near field RF communicator, the magnitude of the complex impedance of the second arm 38' (to the communicator) may be greater than that of the first arm 40'. For example the splitter 906 may provide 70% of the power to the -26 -rectifier and 30% to the communicator. In such a system, the magnitude of the complex impedance of the first arm 40' may have a selected relation to that of the second arm 38', such as that described above with reference to Figure 4. Different splits may be provided.

Although the component values may be different (see below), the splitter shown in Figure 6 has the same structure as that illustrated in Figure 6, other than as follows. In the first arm 40', a third inductor 60 is connected in series between the first inductor 44' and the rectifier coupling 34. A fifth capacitor 62 connects the reference voltage to the connection between the first inductor 44' and the third inductor 60. A sixth capacitor 64 connects the reference voltage to the connection between the third inductor 60 and the rectifier coupling 34.

In the second arm 38', a fourth inductor 66 is connected in series between the second inductor 50' and the chip coupling 32. A seventh capacitor 68 connects the reference voltage to the connection between the second inductor 50' and the fourth inductor 66. An eighth capacitor 70 connects the reference voltage to the connection between the fourth inductor 66 and the chip coupling 32.

The resistor 54' connects the connection between the first inductor 44' and the third inductor 60 to the connection between the second inductor 50' and the fourth inductor 66.

Any combination of capacitors placed in parallel may be combined 30 into a single capacitor with a value that may be the addition of the capacitance of each single capacitor (for example capacitor 42' and 48', capacitor 52' and 68, capacitor 46' and 62) -27 -As to component values, in the system shown in Figure 7, the first capacitor and the second capacitor may have the same capacitance as each other. And, the third capacitor and the fourth capacitor may have the same capacitance as each other, and this may be different to that of the first and second capacitor. The capacitances may all be on the order of tens of pico-farad up to tens of nano-farad, e.g. between 1*10-13F and 1*10-3F. The first inductor and the second inductor may have different inductances from each other, and this may be on the order of nano-henry to tens of micro-henry, e.g. between 1*10 -°1-1 and 1*10 5F. The resistor which connects the two arms together may have a resistance equal to that of the real part of the antenna impedance and/or that of the real part of the output impedance of the input leg.

In Figure 7, it can be seen that the first arm 40' comprises two stages: (i) an input stage comprising the first capacitor 42', first inductor 44', and second capacitor 46'; and (ii) an output stage comprising the fifth capacitor 62, third inductor 60, and sixth capacitor 64. Likewise, the second arm 38' also comprises two stages: (i) an input stage comprising the third capacitor 48', second inductor 50', and fourth capacitor 52'; and (ii) an output stage comprising the seventh capacitor 68, fourth inductor 66, and eighth capacitor 70. The resistor 54' connects (a) the connection between the input stage and the output stage of the first arm to (b) the connection between the input stage and the output stage of the second arm. The division of power between the first arm and the second arm may be controlled by selecting the ratio of the impedance of the input stage of the each arm relative to the output stage of that arm, and by selecting the ratio of the impedance of the input stage of the first arm to the impedance of input stage of the second arm. For example, a ratio of power division, R, may be provided between a 'main branch' arm which takes more of the power from the input leg than a -28 -secondary branch' arm. To achieve this, the magnitude of the impedance of the input stage of the 'main branch' arm may be 1/R of the impedance of the input stage of the 'secondary branch' arm. The 'main branch' arm output stage may have an impedance equal to the 'main branch' arm input stage divided by the square root of (1+R). The 'secondary branch' output stage nay have an impedance equal to the 'main branch' arm input stage divided by the square root of (R*(1+R)).

Any feature of any one of the examples disclosed herein may be combined with any selected features of any of the other examples described herein. For example, features of methods may be implemented in suitably configured hardware, and the configuration of the specific hardware described herein may be employed in methods implemented using other hardware.

It will be appreciated in the context of the present disclosure that lumped components may comprise discrete capacitors and inductors, as distinct from distributed elements such as microstrips or transmission lines which provide spatially distributed capacitance and/or inductance along their length. One example of a lumped component, which may be of particular utility in the provision of flat, low-profile devices such as smart cards, is a printed coil inductor. Such an inductor may comprise a laminar conductive coil on one surface of a dielectric, which follows a spiral path in from an input connection at the outside of the spiral to a connection through the dielectric inside the spiral. On the other side of the dielectric, a second laminar conductive coil may follow a mirror image of the same path out from this connection to an output connection at the outward edge of the spiral. The output connection may also be connected back through the dielectric so that input and output to the inductor may be provided on the same surface of the dielectric. The dielectric may comprise a substrate upon which a circuit is -29 -printed in the manner of a PCB. Other types of printed coil inductors may be used.

It will be appreciated from the discussion above that the embodiments shown in the Figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and/or distributed throughout apparatus of the disclosure. In some embodiments the function of one or more elements shown in the drawings may be integrated into a single functional unit.

In some examples the functionality of the controller may be provided by a general purpose processor, which may be configured to perform a method according to any one of those described herein. In some examples the controller may comprise digital logic, such as field programmable gate arrays, FPGA, application specific integrated circuits, ASIC, a digital signal processor, DSP, or by any other appropriate hardware. In some examples, one or more memory elements can store data and/or program instructions used to implement the operations described herein. Embodiments of the disclosure provide tangible, non-transitory storage media comprising program instructions operable to program a processor to perform any one or more of the methods described and/or claimed herein and/or to provide data processing apparatus as described and/or claimed herein. The controller may comprise an analogue control circuit which provides at least a part of -30 -this control functionality. An embodiment provides an analogue control circuit configured to perform any one or more of the methods described herein.

The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged. 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.

Claims

-31 -Claims 1. A mounting system for a near field RF communications chip, the system comprising: a substrate for carrying electronic components, and for 5 providing electrical interconnections therebetween; a chip coupling carried by the substrate for connecting a near field RF communications chip to the mounting system; an auxiliary power provider, separate from said near field RF communications chip, and adapted for providing electrical 10 power output based on a received alternating electrical signal; and, an antenna coupling for connecting a near field RF communications antenna to said mounting system; and a splitter, for splitting alternating electrical signals, 15 the splitter comprising: a first port connected to the antenna coupling and having a first input impedance; a second port connected to the first port and configured to provide a first part of the alternating electrical signal to the auxiliary power provider; and a third port connected to the first port and configured to provide a second part of the alternating electrical signal to the chip coupling; wherein the splitter is configured to maintain the first 25 input impedance so that: the output impedance of the second port is maintained in the event of fluctuations in the output impedance of the third port; and the output impedance of the third port is maintained in the event of fluctuations in the output impedance of the second port.
2. The mounting system of claim 1, wherein the second port comprises a first terminal and a second terminal, and the third -32 -port comprises a first terminal and a second terminal, and the second port's first terminal and the third port's first terminal are each connected to a common point by a reactive impedance, such as an inductor or capacitor.
3. The mounting system of claim 2 wherein the common point is connected to a first terminal of the first port.
4. The mounting system of claim 2 or 3 wherein the second 10 port's first terminal is connected to the third port's first terminal by a series connection of two inductors to provide RF isolation between the two first terminals.
5. The mounting system of claim 3 or 4 wherein an intermediate part of the series connection of the two inductors is connected to a reference voltage such as ground, for example wherein the second port's second terminal is connected to the third port's second terminal by a series connection of two capacitors.
6. The mounting system of claim 5 wherein a first one of the two capacitors connects the intermediate part of the series connection of the two inductors to the second port's second terminal.
7. The mounting system of claim 5 or 6 wherein a second one of the two capacitors connects the intermediate part of the series connection of the two inductors to the third port's second terminal.
8. The mounting system of any preceding claim wherein the first input impedance is matched to the output impedance of said near field RF communications antenna, and the output impedance of the second port is selected to match the input impedance of the near field RF communications chip.
-33 - 9. The mounting system of any preceding claim wherein the splitter is configured to provide, at the first port, variations in electrical load corresponding to the variations in electrical 5 load at the third port.
10. The mounting system of any preceding claim wherein the splitter is configured so that the first part of the alternating electrical signal comprises more power than the second part of 10 the alternating electrical signal.
11. The mounting system of any preceding claim wherein the splitter comprises a network of lumped components.
12. The mounting system of claim 11 wherein the network comprises a Wilkinson divider.
13. A near field RF communications apparatus comprising: a near field RF communicator; an antenna for coupling with an alternating H-field; an auxiliary rectifier, separate from the near field RF communicator a splitter comprising a network of lumped components, wherein the network is connected to receive an alternating electrical signal from the antenna, and to provide a first part of the alternating electrical signal to the auxiliary rectifier and to provide a second part of the alternating electrical signal to the near field RF communicator.
14. The near field RF communications apparatus of claim 13 wherein the splitter comprises: a first port connected to the antenna and having a first input impedance; -34 -a second port connected, by the network, to the first port and connected to the auxiliary rectifier; and a third port connected, by the network, to the first port and to the near field RF communicator.
15. The near field RF communicator of claim 14, wherein the second port comprises a first terminal and a second terminal, and the third port comprises a first terminal and a second terminal, and the second port's first terminal is at least partially isolated from the third port's first terminal.
16. The mounting system of claim 15 wherein the second port's first terminal is connected to the third port's first terminal by a series connection of two ground isolation inductors to provide 15 RF isolation between the two first terminals.
17. The near field RF communications apparatus of 14, 15, or 16 wherein the splitter is configured so that: the output impedance of the second port is maintained in the event of fluctuations in the output impedance of the third port; and the output impedance of the third port is maintained in the event of fluctuations in the output impedance of the second port.
18. The near field RF communications apparatus of claim 17 wherein the first input impedance is matched to the output impedance of the antenna, and the second port has an output impedance selected to match the input impedance of the near field RF communicator.
19. The near field RF communications apparatus of any of claims 14 to 18 wherein the near field RF communicator is provided by an integrated circuit, such as a chip, that is separate from the splitter.
-35 - 20. A power splitter for a near field RF communications apparatus, the power splitter comprising: a first port for receiving an alternating electrical signal 5 from a near field communications antenna; a second port connected to the first port and configured to provide a first part of the alternating electrical signal to a rectifier of an auxiliary power provider; a third port connected to the first port and configured to provide a second part of the alternating electrical signal to a near field RF communicator to enable the near field RF communicator to communicate via the near field communications antenna; a network of lumped components configured to connect the 15 first port to the second port and the third port, and to provide: an input impedance at the first port which matches the output impedance of the antenna at the first port; an output impedance at the second port which matches the input impedance of the rectifier; and an output impedance at the third port which matches the input impedance of the near field RF communicator.
21. The network of claim 20 wherein the network of lumped components is configured to operate as a Wilkinson divider which 25 splits alternating electrical signals of a near field RF communications frequency band.
22. The network of claim 21 wherein the near field RF communications frequency band comprises 13.56MHz.
23. A smart card for carrying a near field RF communications chip, and a near field RF communications antenna, the smart card comprising: -36 -an auxiliary rectifier separate from the near field RF communications chip for providing electrical power to auxiliary circuitry; a power splitter comprising a network of lumped capacitors 5 and printed coil inductors, wherein the network is connected to receive an alternating electrical signal from the antenna, and to provide a first part of the alternating electrical signal to the auxiliary rectifier and to provide a second part of the alternating electrical signal to the near field RF communicator. 10
24. The apparatus of claim 23 wherein the splitter comprises: a first port for connection to the antenna and having a first input impedance; a second port connected, by the network, to the first port 15 and connected to the auxiliary rectifier; and a third port connected, by the network, to the first port for connection to the near field RF communicator chip.
25. The apparatus of claim 24 wherein the splitter is configured so that: the output impedance of the second port is maintained in the event of fluctuations in the output impedance of the third port; and the output impedance of the third port is maintained in the event of fluctuations in the output impedance of the second port.