Demodulator for contactless chip card

• US 6,031,419 A
• Filed: 09/18/1998
• Issued: 02/29/2000
• Est. Priority Date: 09/23/1997
• Status: Expired due to Term

• Current Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Subbiotto, Frederic, Roberts, Andrews James
• Primary Examiner(s): GRIMM, SIEGFRIED H
• Application Number:
  US09/157,070
• Time in Patent Office: 529 Days
• Field of Search: 329/349, 329/363, 329/364, 329/366, 329/369, 329/370, 235/380, 235/439
• US Class Current: 329/349
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: H04L 25/062 Setting decision thresholds using feedforward techniques only
• CPC Class Codes: H04L 27/08 Amplitude regulation arrangements

Abstract

A contactless chip card, receiving binary data transmitted by radio frequency, includes a demodulator for the binary data. The demodulator includes a circuit for the detection of the transmitted signals, a rectifier circuit, a bandpass filter, two comparators and a memory circuit. The bandpass filter provides a low-frequency signal used as a reference for the two comparators and a high-frequency signal that is compared with the references varying with the low frequency signal. As a result, the demodulation is independent of the mean level of the received signal.

Claims

1. A demodulator of binary data for a contactless chip card with transmission by radio frequency signals, said demodulator comprising:

a detector for receiving a radio frequency signal and generating a detected signal responsive thereto;

a rectifier for generating a rectified signal based upon the detected signal;

a bandpass filter for generating a first signal at low frequency and a second signal at high frequency based upon the rectified signal;

a comparator stage for comparing the first and second signals; and

a memory for storing a result of a comparing by said comparator stage.

2. A demodulator according to claim 1, wherein said comparator stage comprises first and second comparators.

3. A demodulator according to claim 2, wherein the first comparator has a first input connected to a first threshold greater than the first signal and a second input connected to the second signal;

and wherein the second comparator has a first input connected to the second signal and a second input connected to a second threshold lower than the first signal.

4. A demodulator according to claim 3, further comprising a resistor-based voltage divider generating the first and second thresholds.

5. A demodulator according to claim 3, wherein said memory comprises a bistable circuit having a set input terminal connected to an output of said first comparator and having a reset input connected to an output of said second comparator.

6. A demodulator according to claim 1, wherein said bandpass filter comprises:

a high-pass filter having cut-off frequency for passing the binary data without substantial attenuation; and

a low-pass filter having a cut-off frequency for reducing ripple at a carrier frequency and for determining a DC component of the rectified signal.

7. A demodulator according to claim 1, wherein said rectifier comprises a four-branch bridge;

and wherein each branch comprises a diode.

8. A demodulator according to claim 1, wherein said detector comprises an antenna loop and a capacitor connected in parallel therewith.

9. A contactless chip card comprising:

a demodulator comprising

a detector for receiving a radio frequency signal and generating a detected signal responsive thereto;

a rectifier for generating a rectified signal based upon the detected signal;

a bandpass filter for generating a first signal at low frequency and a second signal at high frequency based upon the rectified signal;

a comparator stage for comparing the first and second signals; and

a memory for storing a result of a comparing by said comparator stage.

10. A chip card according to claim 9, wherein said comparator stage comprises first and second comparators.

11. A chip card according to claim 10, wherein the first comparator has a first input connected to a first threshold greater than the first signal and a second input connected to the second signal;

and wherein the second comparator has a first input connected to the second signal and a second input connected to a second threshold lower than the first signal.

12. A chip card according to claim 11, further comprising a resistor-based voltage divider generating the first and second thresholds.

13. A chip card according to claim 11, wherein said memory comprises a bistable circuit having a set input terminal connected to an output of said first comparator and having a reset input connected to an output of said second comparator.

14. A chip card according to claim 9, wherein said bandpass filter comprises:

a high-pass filter having cut-off frequency for passing the binary data without substantial attenuation; and

a low-pass filter having a cut-off frequency for reducing ripple at a carrier frequency and for determining a DC component of the rectified signal.

15. A chip card according to claim 9, wherein said rectifier comprises a four-branch bridge;

and wherein each branch comprises a diode.

16. A chip card according to claim 9, wherein said detector comprises an antenna loop and a capacitor connected in parallel therewith.

17. A demodulator of binary data for a contactless chip card with transmission by radio frequency signals, said demodulator comprising:

a detector for receiving a radio frequency signal and generating a detected signal responsive thereto;

a rectifier for generating a rectified signal based upon the detected signal;

a bandpass filter for generating a first signal at low frequency and a second signal at high frequency based upon the rectified signal, said bandpass filter comprising

a high-pass filter having cut-off frequency for passing the binary data without substantial attenuation, and

a low-pass filter having a cut-off frequency for reducing ripple at a carrier frequency and for determining a DC component of the rectified signal; and

a comparator stage for comparing the first and second signals.

18. A demodulator according to claim 17, wherein said comparator stage comprises first and second comparators.

19. A demodulator according to claim 18, wherein the first comparator has a first input connected to a first threshold greater than the first signal and a second input connected to the second signal;

and wherein the second comparator has a first input connected to the second signal and a second input connected to a second threshold lower than the first signal.

20. A demodulator according to claim 19, further comprising a resistor-based voltage divider generating the first and second thresholds.

21. A demodulator according to claim 18, further comprising a memory for storing a result of a comparing by said comparator stage.

22. A demodulator according to claim 21, wherein said memory comprises a bistable circuit having a set input terminal connected to an output of said first comparator and having a reset input connected to an output of said second comparator.

23. A demodulator according to claim 17, wherein said rectifier comprises a four-branch bridge;

and wherein each branch comprises a diode.

24. A demodulator according to claim 17, wherein said detector comprises an antenna loop and a capacitor connected in parallel therewith.

25. A method for demodulating binary data in a contactless chip card receiving transmission by radio frequency signals, the method comprising the steps of:

receiving a radio frequency signal and generating a detected signal responsive thereto;

generating a rectified signal based upon the detected signal;

generating a first signal at low frequency and a second signal at high frequency based upon the rectified signal;

comparing the first and second signals.

26. A method according to claim 25, further comprising the step of storing a result of the comparing step.

27. A method according to claim 26, wherein the step of comparing comprises:

providing a first comparator having a first input connected to a first threshold greater than the first signal and a second input connected to the second signal; and

providing a second comparator having a first input connected to the second signal and a second input connected to a second threshold lower than the first signal.

28. A method according to claim 27, further comprising the step of generating the first and second thresholds using a resistor-based voltage divider.