Method and apparatus for controlled persistent ID flag for RFID applications

• US 20050237843A1
• Filed: 07/08/2004
• Published: 10/27/2005
• Est. Priority Date: 04/13/2004
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Hyde, John D.
• Granted Patent: US 7,215,251 B2
• Time in Patent Office: Days
• US Class Current: 365/228
• 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 Radio-Frequency Identification (RFID) transponder is provided. The RFID transponder may include a basic ID flag circuit having a VDD voltage node, an output voltage node, and a capacitor coupled to the VDD voltage node and the output voltage node to store an ID flag. A supplemental discharge current circuit coupled to the basic ID flag circuit is provided in order to control persistence duration of the state of the ID flag. The persistence duration of the state of the ID flag is controlled by maintaining supplemental discharge current, which is greater than the leakage current of the basic ID flag circuit.

Claims

1. A Radio-Frequency Identification (RFID) transponder including:

an identification flag circuit to maintain an RFID transponder state, the identification flag circuit including a first capacitor and a digital element coupled to the first capacitor to receive a voltage of the first capacitor; and

a discharge circuit to drain the first capacitor via a discharge current that is distinct from a semiconductor leakage current.

2. The RFID transponder of claim 1, further including a charge circuit, wherein the semiconductor leakage current is through an open switch of the charge circuit.

3. The RFID transponder of claim 1, wherein the digital element is a comparator, the comparator being to output a signal indicative of the identification flag.

4. The RFID transponder of claim 1, wherein the discharge circuit is to maintain the discharge current substantially constant with temperature.

5. The RFID transponder of claim 1, wherein the ID flag circuit further includes a leakage circuit to allow a leakage current to discharge the capacitor in addition to the discharge current.

6. The RFID transponder of claim 1, wherein the discharge current decreases with temperature.

7. The RFID transponder of claim 1, wherein the discharge current is higher than the semiconductor leakage current.

8. The RFID transponder of claim 1, wherein the discharge current is lower than the semiconductor leakage current.

9. The RFID transponder of claim 1, wherein the discharge circuit includes:

a discharge circuit capacitor to store voltage; and

a transconductor circuit coupled to the discharge circuit capacitor to convert voltage stored on a discharge circuit capacitor into the discharge current.

10. The RFID transponder of claim 9, wherein the transconductor circuit includes:

a first transistor having a gate, a source and a drain, the gate coupled to the discharge circuit capacitor; and

a second transistor having a gate, a source and a drain the gate coupled to the discharge circuit capacitor.

11. The RFID transponder of claim 10, wherein the discharge circuit capacitor is to store the gate voltage of the first transistor and the gate voltage of the second transistor responsive to detection of power loss on the RFID transponder.

12. The RFID transponder of claim 10, wherein the first transistor and the second transistor are NMOS transistors.

13. The RFID transponder of claim 10, wherein a W/L ratio of the second transistor is smaller than a W/L ratio of the first transistor.

14. The RFID transponder of claim 9, wherein the discharge circuit includes a discharge circuit switch coupled to the discharge circuit capacitor and adapted to open responsive to detection of power loss on the RFID transponder.

15. The RFID transponder of claim 1, further including a digital non-volatile memory to control accuracy of the discharge current.

16. The RFID transponder of claim 1, further including an output voltage node coupled to the digital element, the output voltage node indicating an identification flag state.

17. The RFID transponder of claim 16, wherein the identification flag state persists during a power loss at the RFID transponder for a predetermined period of time.

18. The RFID transponder of claim 16, wherein the predetermined period of time is more than or equal to 500 milliseconds.

19. The RFID transponder of claim 16, wherein the predetermined period of time is less than or equal to 20 seconds.

20. The RFID transponder of claim 16, wherein the identification flag state persists during a power loss at the RFID transponder for the predetermined period of time at temperatures between negative 25 degrees Celsius and 50 degrees Celsius.

21. The RFID transponder of claim 16, wherein the identification flag state is represented by a single bit.

22. A method to control persistence of an RFID transponder state, comprising:

charging to a supply voltage a capacitor operative to indicate the RFID transponder state; and

draining the capacitor with a discharge current distinct from a semiconductor leakage current from an open switch.

23. The method of claim 22, wherein the capacitor is charged responsive to responding to an interrogation signal.

24. The method of claim 22, further comprising:

additionally draining the capacitor with the semiconductor leakage current.

25. The method of claim 22, wherein the discharge current is higher than the semiconductor leakage current.

26. The method of claim 22, wherein the discharge current is lower than the semiconductor leakage current.

27. The method of claim 22, wherein the RFID transponder state persists during a power loss at the RFID transponder for a predetermined period of time.

28. The method of claim 27, wherein the predetermined period of time is more than or equal to 500 milliseconds.

29. The method of claim 27, wherein the predetermined period of time is less than or equal to 20 seconds.

30. The method of claim 27, wherein the RFID transponder state persists during a power loss at the RFID transponder for the predetermined period of time at temperatures between negative 25 degrees Celsius and 50 degrees Celsius.

31. The method of claim 22, wherein the RFID transponder state is represented by a single bit.

32. A device to control persistence of an RFID transponder state, comprising:

means for charging to a supply voltage a capacitor operative to indicate the RFID transponder state; and

means for draining the capacitor with a discharge current distinct from a semiconductor leakage current from an open switch.

33. The device of claim 32, wherein the capacitor is charged responsive to responding to an interrogation signal.

34. The device of claim 32, further comprising:

means for additionally draining the capacitor with the semiconductor leakage current.

35. The device of claim 32, wherein the discharge current is higher than the semiconductor leakage current.

36. The device of claim 32, wherein the discharge current is lower than the semiconductor leakage current.

37. The device of claim 32, wherein the RFID transponder state persists during a power loss at the RFID transponder for a predetermined period of time.

38. The device of claim 37, wherein the predetermined period of time is more than or equal to 500 milliseconds.

39. The device of claim 37, wherein the predetermined period of time is less than or equal to 20 seconds.

40. The device of claim 37, wherein the RFID transponder state persists during a power loss at the RFID transponder for the predetermined period of time at temperatures between negative 25 degrees Celsius and 50 degrees Celsius.

41. The device of claim 32, wherein the RFID transponder state is represented by a single bit.