Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/0008—General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Definitions

• This invention relates to a transaction system in which a portable token, for example a
• the card is used in conjunction with a device, often termed a terminal, to perform a transaction of some kind.
• a device often termed a terminal
• the invention is particularly, but not exclusively, related to
• Contactless tokens work on, or close to, a terminal which provides power. This power is supplied via a RF (radio frequency) induction field which is referred to as a carrier signal which is transmitted from the terminal to the token. Transfer of power from the terminal to the token is akin to the terminal being a primary coil of a transformer and the token a secondary coil. In particular embodiments both the terminal and the token typically each have a single coil aerial
• data is transmitted from the terminal to the token and vice versa. Exchange of the data is used to perform a transaction. Transmission of data from the
• Transmission of a data signal from the token to the terminal may be
• Data receiving means in the terminal derives the data signal sent by
• a problem in such systems is that the amplitude of the data signal from the token received by the terminal is weak in comparison to the amplitude of the carrier signal. If the terminal modulates another signal onto the carrier signal, such as a tone which is to be used by the token to derive a clock, the data signal will be weak in comparison to this other signal as well.
• the weakness of the data signal is a problem because the carrier signal from the terminal is being transmitted at the same time as the data signal from the token and the token and the terminal each have only one aerial. Therefore, the signals are both present at the reader aerial. As the token is powered further from the terminal, the power level of the carrier signal remains approximately the same and the power level of the data signal at the reader aerial decreases.
• the ratio of the received data signal to the carrier signal becomes lower as the token moves away from the terminal aerial.
• the ratio of the data signal to the carrier signal is less than 1%.
• Another solution is to provide the token and the terminal each with two aerials, one to transmit and one to receive.
• the terminal and the token is preferred because this enables the terminal and the token to communicate to each other in any orientation. This provides advantages in simplicity and compactness, particularly for the token.
• the carrier signal is an original carrier signal generated in the terminal. It is not limited to the carrier signal
• the first carrier signal is transmitted to the token.
• the first carrier signal is created by modifying the carrier signal.
• the first carrier signal is created using a low pass filter.
• the second carrier signal is created by modifying the carrier signal.
• the first and second carrier signals are substantially 180° out of phase.
• the first and second carrier signals cancel each other out.
• phase shifters are used to generate the first and second carrier signals.
• one or more filters is used.
• first filter means is used to generate the first carrier signal and second filter means is used to generate the second carrier signal.
• the first filter means may comprise a low pass filter in the terminal. It may filter out harmonics from the carrier signal to produce the first carrier signal. These harmonics may originate from a clock signal which is used to generate the carrier signal.
• the second filter means which is used to produce the second carrier signal may comprise a high pass filter in the terminal.
• the first filter means may be arranged so as to induce a phase shift in the first carrier signal.
• the second filter means is designed to induce a phase shift of (x+180)° in the second carrier signal, so
• first carrier signal and the second carrier signal are substantially completely out of phase.
• the terminal is also able to cancel another signal or other signals present on the carrier signal such as a tone signal which is used to provide a clock on the token.
• the tone signal is independent of the carrier signal itself.
• the terminal and the token have a common inductive coupling which is used to transmit from the terminal to the token and vice versa.
• the coils of the terminal and the token may each have one or more turns. Conveniently both the terminal and the token each have only one coil aerial.
• the invention provides a terminal according to the first aspect of the invention.
• the invention provides a method of reducing the level of the first carrier signal at the data receiving means according to the first aspect of the invention.
• the invention provides a method of modulating a carrier signal used in a transaction system which comprises a terminal having an inductive
• carrier source signal to generate the carrier signal characterised in that the method comprises the steps of adding together the carrier source signal and a modulating signal to produce a summed signal rectifying the summed signal to produce a rectified summed 6 signal and then processing the rectified summed signal to produce a modulated carrier
• the invention provides a transaction system and/or a terminal
• the summed signal is rectified by sending it through a transistor.
• the transistor is a switch for a tank circuit.
• the tank circuit fills in the missing half of the rectified summed signal.
• the tank circuit may also remove harmonics which are present.
• the invention provides a transaction system and/or a terminal which uses the method of the sixth aspect of the invention.
• the invention provides a transaction system comprising 7 a terminal having an inductive coupling and a token for communicating with the terminal the token having an inductive coil for receiving from the terminal a carrier
• a source signal used to produce the carrier signal is passed through a band stop filter the filter being arranged so as to filter at least one frequency being substantially equal to at least one frequency of the data transmitted by the token.
• the source signal is a modulation signal which is used to modulate a carrier source signal.
• the invention provides a method of filtering a carrier signal according to the eighth aspect of the invention.
• the filter removes data or clock harmonics or both from the source signal.
• Figure 1 shows a schematic representation of the transaction system
• Figure 2 shows a transmitter and receiver circuit in the terminal
• Figure 3 shows a modulation circuit in the terminal
• Figure 4 shows an alternative modulation circuit in the terminal.
• a carrier signal modulated with data In known contactless transaction systems it is usual for a carrier signal modulated with data to pass through a power amplifier in a terminal and then be sent directly to an aerial 8 in the terminal for transmission.
• the terminal aerial is directly connected to a data receiving means such as a data receiving circuit to receive a data signal which has been modulated onto the carrier signal by a token.
• the data receiving circuit has to
• the frequency of the carrier signal is detected and used by the token to derive a clock for the token.
• the carrier signal is additionally modulated with a tone signal which is received by and used by the token to generate a clock.
• a tone signal is not as strong as the carrier signal, it is still considerably stronger than the data signal from the token, typically 1.5V. The tone signal can cause further difficulty in the terminal receiving the data signal because it is generally much closer in frequency to the frequency of the data signal.
• FIG. 1 shows a transaction system 10 comprising a terminal 12 and a token, such as a smart card, 14.
• the terminal 12 has a carrier source 16 and a modulation source 18.
• the modulation source 18 produces a modulation signal 20 which is a data signal.
• modulation signal 20 may contain raw data 22 such as transaction related information
• the clock signal may be present
• a carrier modulator 26 uses the modulation signal 20 to modulate a carrier source signal 28 produced by the carrier source 16. As a result the carrier modulator 26 produces a modulated carrier signal 30 9 which is transmitted by an aerial 32 to be received by the token 14.
• the token 14 has an aerial 34 and an interface 36 which is connected to a controller 38
• the aerial 34 receives the modulated carrier signal 30 and
• the interface 36 and thus the controller 38, extracts a clock and a data signal 40 and power 42.
• the controller 38 processes the data signal 40 to produce its own data to be transmitted to the terminal 12 to conduct a transaction.
• Transmission of data from the token to the terminal is carried out by switching an impedance 43 across the aerial 34 and thus changing the amount of power drawn by the token 14 from the carrier signal of the terminal 12.
• the terminal 12 receives a signal representative of the impedance switching and detects the token data in data receiving means or a detector 44. Extracted data 46 is then processed by the terminal 12.
• FIG. 2 shows particular detail of the system of Figure 1 and shows a transmitter and receiver circuit 50 in the terminal.
• the circuit 50 transmits power and data and receives data.
• the modulation signal 20 and the carrier source signal 28 are both received by a power amplifier 52 such that the carrier source signal 28 is modulated by the modulation
• the power amplifier 52 produces the modulated carrier signal 30.
• the modulated carrier signal 30 is split into two signals 54 and 56, one of which is fed
• phase of the signal 54 (and of its sidebands) 10 is shifted by x° (typically -120°) to produce phase shifted signal 62.
• filter 58 attenuates harmonics of the transmitted carrier signal thus helping compliance
• phase shifted signal 64 The frequency of the carrier signal does not vary and the person skilled in the art would readily be able to design the filters 58 and 60 to provide the desired phase shifts at the carrier signal frequency.
• the phase shifted output 62 is used to drive the aerial 32. Since there is only a single aerial 32, not only does this receive the phase shifted signal 62 but it also receives a data signal 66 from the token 14. Conventionally the detector 44 receives a mixture of amplified modulated carrier signal 30 and received data signal 66. The modulated carrier signal 30 is much greater in magnitude than the data signal 66 and so the data signal 66 is usually difficult to detect. This difficulty increases as the token 14 is located further away from the terminal 12. However, in the present embodiment of the invention, the detector 44 receives a summation 68 of signals 62, 64 and 66. As signals 62 and 64 substantially cancel at summation 68 their magnitude is significantly reduced.
• data signal 66 is unaffected by this cancellation and therefore the ratio of the data signal 66 to the signal 62 (which is transmitted as the carrier signal) is greater than
• the circuit 50 of Figure 2 can readily be incorporated into the terminal 12 of Figure 1. 11
• the power amplifier 52 serves as the carrier modulator 26 and has the same inputs 20 and 28.
• the additional features of circuit 50 can be accommodated to provide a single
• the transaction system described above produces a modulated carrier signal to send information, such as transaction data or a clock or both, to the token.
• Amplitude modulation of the carrier signal is often used.
• One known way of applying amplitude modulation is to add sidebands containing information (such as transaction data or a clock or both) to the carrier signal and then amplify the modulated carrier signal.
• Another way is to multiply the modulation signal with the carrier source signal as it is being produced. This can be done by feeding the modulation signal directly into the input of a power amplifier such as power amplifier 52 in Figure 2.
• a method of modulating the carrier signal according to an aspect of the invention will now be described in relation to Figure 3. This method can be used in a transaction system having the inventive aspects of Figures 1 and 2 or it may be applied to prior art systems on its own without these aspects.
• a carrier source signal 28 and a modulation signal 20 are added together by using two resistors 70 and 72.
• the modulation signal 20
• the oscillator is generated by a crystal oscillator and typically has a frequency of 13.56 MHz.
• signal 28 could be at 10V and signal 20 at 1.5V. This is not amplitude modulation but is rather a summation.
• the signals 20 and 28 add together to produce a combined signal 74 which is fed into a transistor 76 which controls a tank circuit 78.
• a tank circuit is a 12 tuned circuit for storing charge which usually comprises a capacitor and an inductor. If bias levels of the transistor 76 are set correctly, the base/emitter diode of the transistor
• signal 80 uses signal 80 to produce a mirror image resulting in an amplitude modulated signal 82.
• the signal 82 is then amplified by power amplifier 84 and supplied to the aerial 32. Alternatively, if of sufficient magnitude, the signal 82 could be applied directly to the
• An alternative method of modulating the modulation signal 20 onto the carrier source signal 28 is to modulate directly a power supply which powers a circuit producing the carrier signal.
• a means of doing this is shown in Figure 4.
• a steady power supply 86 for example 12V, feeds a FET 88 to produce a regulated power supply 90. This in turn supplies power to a tank circuit 94.
• the FET 88 is controlled by a high speed operational amplifier 96.
• the operational amplifier 96 uses its high gain to maintain power supply 90 close to an input 100.
• Input 100 is simply a summation of a DC voltage 102 (derived from a bandgap device for example) and the
• the spectral purity 13 of the output that is the amplitude modulated carrier, is better than in known two step methods. This is because the tank circuit ensures that the fundamental carrier signal
• a further inventive aspect of the transaction system is described below. Again, although it may be applied to the embodiments of Figures 1, 2 and 3 or Figures 1, 2 and 4, it may equally be applied to prior art transaction systems on its own.
• Data is sent from the token to the terminal using a separate tone at for example 847.5kHz by modulating an impedance in the token.
• This frequency is a standard figure which represents a sixteenth of a typical carrier frequency of 13.56 MHz. Since the token data is at a low power level when received at the terminal, any noise at or around this frequency present on a signal being sent to the token, whether it be on the carrier signal or on any data modulating it, will make it more difficult for token data to be detected. Therefore a band stop filter 92 is placed before the carrier modulator 26, 52 so as to filter the

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• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Near-Field Transmission Systems (AREA)
• Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

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• 1998
  • 1998-01-24 GB GB9801439A patent/GB2333665B/en not_active Expired - Fee Related
• 1999
  • 1999-01-22 EP EP99901794A patent/EP0972265A1/de not_active Withdrawn
  • 1999-01-22 WO PCT/GB1999/000239 patent/WO1999038106A1/en not_active Application Discontinuation
  • 1999-01-22 AU AU21791/99A patent/AU2179199A/en not_active Abandoned

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