GB2308948A

GB2308948A - Data Transfer Circuit

Info

Publication number: GB2308948A
Application number: GB9600257A
Authority: GB
Inventors: Michel Burri; Hans Staufer
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1996-01-06
Filing date: 1996-01-06
Publication date: 1997-07-09
Anticipated expiration: 2016-01-06
Also published as: GB2308948B; GB9600257D0

Abstract

A data transfer circuit (10) has an arrangement for receiving a modulated signal, a first current path (25, 30, 35) for providing a first polarity portion of the modulated signal to provide power to the circuit, and a second current path (40, 45, 50, 55) for providing a second polarity portion of the modulated signal to derive modulation information therefrom.

Description

DATA TRANSFER CIRCUIT AND METHOD Field of the Invention This invention relates to data transfer circuits, and particularly though not exclusively to contactless data transfer circuits.

Background of the Invention Contactless smartcard systems are known which provide for transfer of data from a base station to a smartcard and vice-versa without direct electrical coupling. Inductive couplings in the base station and smartcard are typically used to achieve a contactless interface.

In many smartcard applications the smart card itself is arranged to not contain any intrinsic power. Power and data are transferred by a modulated carrier signal via the inductive coupling. The smartcard then switches an internal resistor which can be sensed by the base station. In this way data is transferred back from the smartcard to the base station.

A problem with the above arrangement is that derivation of power from the carrier signal induced within the smartcard causes clipping of the carrier signal.

Furthermore, typical modulation schemes are problematic. Amplitude modulation of the carrier results in power transfer inefficiency, since each logic zero value modulated on the carrier results in a reduced amplitude.

Phase shift modulation causes discontinuities in the carrier signal during phase shift, which necessitates the provision of a phase locked loop to maintain an internal clock in the smartcard.

This invention seeks to provide a data transfer circuit and method which mitigate the above mentioned disadvantages.

Summary of the Invention According to a first aspect of the present invention there is provided a data transfer circuit for receiving a modulated signal, comprising: means for receiving the modulated signal; a first current path for carrying a first polarity portion of the modulated signal to provide power to the circuit; a second current path for providing a second polarity portion of the modulated signal to derive modulation information therefrom.

Preferably the means for receiving the modulated signal comprises an inductor, arranged to produce an induced signal in response to received radiation. The first and second current paths are preferably formed with diodes.

According to a second aspect of the present invention there is provided method for transferring data from a transmitter circuit to a receiver circuit, comprising the steps of: in the transmitter circuit, modulating a carrier signal with data to be transferred; transferring the modulated signal from the transmitter circuit to the receiver circuit; using a first polarity portion of the modulated signal for providing power to the receiver circuit; and, using a second polarity portion of the modulated signal for deriving modulation information in the receiver circuit.

Preferably the modulation information includes data modulated on to the carrier signal and a clock signal. The modulation is preferably amplitude modulation.

In this way clipping of the carrier signal is substantially avoided, power transfer efficiency is increased, and the need for a phase locked loop in the receiver circuit is avoided.

Brief Description of the Drawing(s) An exemplary embodiment of the invention will now be described with reference to the single figure drawing which shows a preferred embodiment of a data transfer system in accordance with the invention.

Detailed Description of a Preferred Embodiment Referring to FIG.1, there is shown a data transfer system 5 including a data transfer circuit 10 and a base station 100. The base station 100 comprises a data input terminal 115 for receiving data to be transmitted to the data transfer circuit 10. A transmitter circuit 110 is coupled to the data input terminal 115, for modulating a carrier frequency signal by the data to be transmitted.

A driver circuit 120 is coupled to receive the modulated signal, for driving it through an inductor 140 via a resistor 125 and a capacitor 130. A potential divider network of resistors 155 and 160 are coupled across the inductor 140, for providing a point of divided potential. A demodulator circuit 150 is coupled to the point of divided potential, for demodulating signals from the inductor 140. A data output terminal 170 is coupled to receive demodulated data from the demodulator 150.

The data transfer circuit 10 comprises an inductor 20 having first and second terminals 22 and 24 respectively, and having a capacitor 12 and a switched resistor 15 coupled in parallel across the first and second terminals 22 and 24.

A first diode 25 is coupled to the first terminal 22, for providing a positive voltage path providing power supply voltage Vdd. A storage capacitor 30 is coupled between the positive voltage path and ground. A second diode is coupled between ground and the second terminal 24 of the inductor 20, for providing a return path for the positive voltage path.

A third diode 40 provides a negative voltage path to be further described below. A fourth diode 45 provides a return path for the negative voltage path.

A clock recovery circuit 50 is coupled to the negative voltage path. A data recovery circuit 55 is also coupled to the negative voltage path. The data recovery circuit comprises a filter 60 coupled to the negative voltage path, an integrator coupled to the filter 60, and a comparator 70, coupled to compare an output of the integrator 65 with an output of the filter 60.

In operation, data to be transmitted to the data transfer circuit 10 is received at the data input terminal 115. The transmitter circuit 110 modulates the carrier frequency signal by this data, and the driver circuit 120 drives it through the inductor 140.

The inductor 20 of the data transfer circuit 10 receives the modulated signal by induction. The first diode 25 and the second diode 35 steer current during the positive phase of the modulated signal to charge the storage capacitor 30 and to provide the operating voltage Vdd to the data transfer circuit 10. The storage capacitor 30 discharges during the negative phase of the modulated signal, thus maintaining Vdd.

The third diode 40 and the fourth diode 45 steer current during the negative phase of the modulated signal to the clock recovery circuit 50 and to the data recovery circuit 55, where the data and clock respectively are recovered.

In this way the current drawn for Vdd does not result in any denigration of the signal to be demodulated. The negative phase is not at risk from clipping, as no current is drawn for Vdd from this phase. This allows the clock to be successfully derived. Furthermore, noise associated with the derivation of Vdd is prevented from being transferred to the data or the clock.

The data transfer circuit 10 is arranged to transfer data back to the base station by using the switched resistor 15 to vary the impedance of the inductor 20. With the switched resistor 15 in a first position, a first impedance is presented, and in a second position, a second impedance is presented. In this way data values of logical 1 and logical 0 can be communicated back to the base station 100.

Response data is transferred back from the data transfer circuit 10 to the base station 100 by mutual inductance of the inductors. The potential divider network of resistors 155 and 160, sense a voltage in the inductor 140, which is dependent upon the mutual inductance received back from the inductor 20. The demodulator circuit 150 demodulates the inductor voltage to provide the received data to the data output terminal 170.

It will be appreciated by a person skilled in the art that alternate embodiments to the one described above are possible. For example, the positive and negative phases and the diodes could be reversed. The inductors could be replaced by other media suitable for contactless data transfer, such as infra-red apparatus.

Claims

1. A data transfer circuit for receiving a modulated signal, comprising: means for receiving the modulated signal; a first current path for carrying a first polarity portion of the modulated signal to provide power to the circuit; a second current path for providing a second polarity portion of the modulated signal to derive modulation information therefrom.

2. The circuit of claim 1 wherein the means for receiving the modulated signal comprises an inductor, arranged to produce an induced signal in response to received radiation.

3. The circuit of claim 1 or claim 2 wherein the first and second current paths are formed with diodes.

4. A method for transferring data from a transmitter circuit to a receiver circuit, comprising the steps of: in the transmitter circuit, modulating a carrier signal with data to be transferred; transferring the modulated signal from the transmitter circuit to the receiver circuit; using a first polarity portion of the modulated signal for providing power to the receiver circuit; and, using a second polarity portion of the modulated signal for deriving modulation information in the receiver circuit.

5. The circuit or method of any preceding claim wherein the modulation information includes data modulated on to the carrier signal.

6. The circuit or method of any preceding claim wherein the modulation information includes a clock signal.

7. The circuit or method of any preceding claim wherein the modulation is amplitude modulation.

8. A circuit substantially as hereinbefore described and with reference to the drawings.

9. A method substantially as hereinbefore described and with reference to the drawings.