Method and apparatus for controlled persistent ID flag for RFID applications

• US 7,116,240 B2
• Filed: 08/18/2004
• Issued: 10/03/2006
• Est. Priority Date: 04/13/2004
• Status: Active Grant

• Current Assignee: Impinj, Inc.
• Original Assignee: Impinj, Inc.
• Inventors: Hyde, John D.
• Primary Examiner(s): Lieu, Julie Bichngoc
• Application Number:
  US10/921,758
• Publication Number:
  US 20050237844A1
• Time in Patent Office: 776 Days
• Field of Search: None
• US Class Current: 340/661
• 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. The persistence duration of the state of the ID flag is controlled by maintaining a charge and leakage circuit. The charge and leakage circuit includes an NMOS device having a source, a drain and a gate, the source node of the NMOS device being coupled to the capacitor and the drain node of the NMOS device being coupled to a first CMOS inverter. The first CMOS inverter is powered by a regulated supply voltage such that the voltage on the capacitor is not dependent on the forward voltage drop of the NMOS device.

Claims

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

a capacitor;

a digital element coupled to the capacitor to receive a voltage of the capacitor; and

a charge and leakage circuit including an NMOS device having a source, a drain and a gate, the source node of the NMOS device being coupled to the capacitor and the drain node of the NMOS device being coupled to a first CMOS inverter,

wherein the first CMOS inverter is powered by a regulated supply voltage such that the voltage on the capacitor is substantially not dependent on the forward voltage drop of the NMOS device.

2. The RFID transponder of claim 1, wherein the regulated supply voltage is lower than VDD.

3. The RFID transponder of claim 1, wherein the regulated supply voltage is more constant than VDD at predetermined temperatures range.

4. The RFID transponder of claim 1, wherein the capacitor is being charged to the regulated supply voltage when the VDD voltage reaches a threshold voltage.

5. The RFID transponder of claim 1, wherein the gate node of the NMOS device is coupled to a second CMOS inverter, wherein the second CMOS inverter is powered by VDD.

6. The RFID transponder of claim 1, wherein the NMOS device is an NMOS switch, the NMOS switch being switched by the second CMOS inverter.

7. The RFID transponder of claim 1, wherein the digital element is a comparator.

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

9. The RFID transponder of claim 8, wherein the identification flag state persists during a power loss at the RFID transponder for a predetermined period of time.

10. The RFID transponder of claim 9, wherein the predetermined period of time is more than or equal to 250 milliseconds.

11. The RFID transponder of claim 9, wherein the predetermined period of time is less than or equal to 2.5 seconds.

12. The RFID transponder of claim 8, 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.

13. The RFID transponder of claim 8, wherein the identification flag state is represented by a single bit.