STATE STORAGE WITH DEFINED RETENTION TIME

• US 20080101106A1
• Filed: 10/31/2006
• Published: 05/01/2008
• Est. Priority Date: 10/31/2006
• Status: Active Grant

• Current Assignee: Hirohiko Kuratsune, Intermec IP Corporation (Honeywell International Inc.), Soiken, Inc., Yasuyoshi Watanabe
• Original Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Inventors: Pillai, Vijay
• Granted Patent: US 7,710,798 B2
• Time in Patent Office: Days
• US Class Current: 365/104
• CPC Class Codes: G11C 11/401 forming cells needing refreshing or charge regeneration, i.e. dynamic cells

Abstract

A state storage device for use in an RFID tag includes, in at least one embodiment, a capacitor coupled to a high impedance node. The storage device can be configured to indicate a high or low bit condition. The high impedance node can be designed to dissipate the stored electrical charge at a user-controlled, predefined, or known rate. The state storage device can be configured to store the bit condition for no more than four seconds. In some embodiments, the high impedance node can be formed from an electrically trimmed transistor.

Claims

1. A state storage device for an RFID tag, comprising:

a state storage capacitor for storing a charge; and

a high impedance node coupled to the state storage capacitor and to a voltage source,

wherein the high impedance node dissipates the stored charge at a substantially constant rate, and wherein the state storage device is manufactured or configured to maintain the charge at the state storage capacitor for a predetermined time period.

2. The state storage device of claim 1, wherein the high impedance node comprises an electrically trimmed transistor.

3. The state storage device of claim 2, wherein the high impedance node further comprises a diode-connected transistor.

4. The state storage device of claim 1, wherein the state storage device is configured to store a flag condition.

5. The state storage device of claim 1, wherein the state storage device is configured to store an EPC RFID Class-1 Generation-2 select flag asserted by a reader.

6. The state storage device of claim 1, wherein the state storage device is configured to store a bit value for a length of time within approximately 500 milliseconds to 5 seconds.

7. The state storage device of claim 1, wherein the state storage device is configured to store a flag condition for a time period not to exceed a time required for a first interrogation round.

8. The state storage device of claim 1, wherein the state storage device is configured to store a flag condition for a time period not to exceed four seconds.

9. The state storage device of claim 1, wherein the state storage device is configured to store a bit condition for a user-defined time period controlled by current dissipation at a user-selectable rate.

10. The state storage device of claim 9, wherein the user-defined time is communicated to the state storage device by an RFID reader.

11. The state storage device of claim 1, wherein the device further comprises:

a controller for controlling a dissipation rate of the charge at the state storage capacitor; and

a receiver for receiving a command to discharge the state storage capacitor at an end of an identification cycle.

12. The state storage device of claim 1, wherein the device further comprises:

multiple state storage capacitors; and

multiple switches coupled to the multiple state storage capacitors for selecting one or more of the capacitors.

13. A method for storing a state on an RFID tag, comprising:

storing a state storage bit value on the RFID tag; and

dissipating the state storage bit at a substantially constant and substantially predetermined rate.

14. The method of claim 13, further comprising receiving a command from a reader to reset the state storage bit value.

15. The method of claim 13, further comprising receiving a command from a reader to select one of multiple state storage capacitors.

16. The method of claim 13, further comprising receiving a command from a reader to reset the state storage bit value at the end of a first identification cycle.

17. The method of claim 13, further comprising storing the bit value for a length of time within approximately 500 milliseconds to 5 seconds.

18. The method of claim 13, further comprising storing the bit value as a flag condition for a time period not to exceed the time required for a first interrogation round.

19. The method of claim 13, further comprising receiving a command from a reader specifying a length of time for which to store the state storage bit value on the RFID tag.

20. An RFID reader, comprising:

a radio for communicating with multiple RFID tags;

a processor configured to generate a state storage bit reset command; and

a radio for transmitting the reset command to at least some of the multiple RFID tags.

21. The RFID reader of claim 20, further comprising data storage for storing an indication of the duration of time for which charge can be retained by a state storage device on a tag.

22. An RFID tag, comprising:

means for storing data;

state storage means for storing a state value;

radio means for at least receiving RF energy; and

control means, coupled among the memory, state storage, and radio means, for controlling the RFID tag, wherein the radio means is configured to receive the RF energy, and wherein the state storage means is configured to store at least a portion of the RF energy for a substantially predetermined time.

23. The RFID tag of claim 22, further comprising means for dissipating the stored energy at a substantially constant rate.