RECEIVER CIRCUIT AND METHOD FOR A CONTACTLESS IDENTIFICATION SYSTEM

• US 20030085278A1
• Filed: 11/08/2001
• Published: 05/08/2003
• Est. Priority Date: 11/08/2001
• Status: Active Grant

• Current Assignee: EM Microelectronic
• Original Assignee: EM Microelectronic
• Inventors: Schoenbauer, Steve
• Granted Patent: US 6,565,001 B1
• Time in Patent Office: Days
• US Class Current: 235/451
• 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

Abstract

A receiver circuit (30) for a contactless identification system, includes an antenna (32). The antenna (32) receives an amplitude modulated signal. A voltage envelope detector (34) is connected to the antenna (32). A current envelope detector (36) is connected to the antenna (32). A first comparator (38) has a first input (40) connected to an output of the voltage envelope detector (34) and a second input (42) connected to a threshold. A second comparator (44) has a first input (46) connected to an output of the current envelope detector (36) and a second input (48) connected to the threshold. A logic gate (50) combines an output (52) of the first comparator (38) and an output (54) of the second comparator (44).

Claims

1. A receiver circuit for a contactless identification system, comprising:

an antenna receiving an amplitude modulated signal;

a voltage envelope detector connected to the antenna;

a current envelope detector connected to the antenna;

a first comparator having a first input connected to an output of the voltage envelope detector and a second input connected to a threshold;

a second comparator having a first input connected to an output of the current envelope detector and a second input connected to the threshold; and

a logic gate combining an output of the first comparator and an output of the second comparator.

2. The circuit of claim 1, wherein the current envelope detector includes a shunt regulator connected to the antenna.

3. The circuit of claim 2, wherein a shunt voltage of the shunt regulator is connected to a voltage envelope follower.

4. The circuit of claim 3, wherein the shunt regulator includes a bleed transistor connected to the antenna.

5. The circuit of claim 4, wherein the shunt regulator includes a control path in parallel with the bleed transistor, the control path having a transistor connected to the antenna, a first resistor connected to the transistor and a second resistor connected between the first resistor and a ground.

6. The circuit of claim 5, wherein the shunt voltage is measured at a node between the transistor and the first resistor.

7. The circuit of claim 6, wherein a gate of the bleed transistor is connected to a node between the first resistor and the second resistor.

8. The circuit of claim 7, wherein the shunt regulator includes a trigger path in parallel with the control path, the trigger path including a mirror diode connected to the antenna and the transistor of the control path, a second diode connected to the mirror diode and a third diode connected between the second diode and the ground.

9. The circuit of claim 1, wherein the logic gate is an AND gate.

10. The circuit of claim 1, further including a biaser system connected to the first comparator and the second comparator.

11. A method of operating a receiver for a contactless identification system, comprising the steps of:

(a) converting an electromagnetic field into an electrical signal;

(b) determining a voltage envelope of the electrical signal to form a voltage envelope signal;

(c) determining a current envelope of the electrical signal to form a current envelope signal; and

(d) combining the voltage envelope signal and the current envelope signal to form an output signal.

12. The method of claim 11, wherein step (a) further includes the step of:

(a1) rectifying the electrical signal.

13. The method of claim 11, wherein step (b) further includes the step of:

(b1) limiting a voltage of the electrical signal by a shunt regulator.

14. The method of claim 13, wherein step (c) further includes the step of:

(c1) detecting a voltage of the shunt regulator to form a current signal.

15. The method of claim 11, wherein step (d) further includes the steps of:

(d1) comparing the voltage envelope signal to a first threshold to form a clean voltage signal;

(d2) comparing the current envelope signal to a second threshold to form a clean current signal.

16. The method of claim 15, further including the steps of:

(d3) logically combining the clean voltage signal and the clean current signal.

17. A receiver circuit for a contactless identification system, comprising:

an antenna;

a voltage envelope detector connected to the antenna;

a current envelope detector connected to the antenna; and

a demodulation system connected to an output of the voltage envelope detector and the current envelope detector.

18. The receiver circuit of claim 17, wherein the current envelope detector includes a shunt regulator connected to the antenna.

19. The receiver circuit of claim 18, wherein the current envelope detector includes an envelope follower connected to the shunt regulator.

20. The receiver circuit of claim 17, wherein the demodulation system includes:

a first comparator having a first input connected to an output of the voltage envelope detector and a second input connected to a first threshold;

a second comparator having a first input connected to an output of the current envelope detector and a second input connected to a second threshold.

21. The receiver circuit of claim 20, further including a logic gate having a first input connected to an output of the first comparator and a second input connected to an output of the second comparator.