State storage with defined retention time

• US 7,710,798 B2
• Filed: 10/31/2006
• Issued: 05/04/2010
• 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
• Primary Examiner(s): Elms; Richard
• Assistant Examiner(s): Byrne; Harry W
• Application Number:
  US11/555,114
• Publication Number:
  US 20080101106A1
• Time in Patent Office: 1,281 Days
• Field of Search: 340 21- 28, 340 101- 106, 340/10.51, 3405721-5729, 700/215, 700/221, 700/225, 700/227, 365/192, 365/104, 455/150.1, 455/151.1, 235375-385, 235/492, 726/20
• US Class Current: 365/192
• 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 capacitor for storing charge; and

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

wherein the state storage device is configured to permit the charge stored in the capacitor to be sensed externally from the RFID tag by an RFID reader;

wherein the high impedance node dissipates the charge stored in the capacitor at a substantially constant rate, and

wherein the state storage device is manufactured or configured to maintain the charge stored in the 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 1, wherein the high impedance node 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 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 period 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 stored in the 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 capacitors; and

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

13. A device for use in an RFID tag to store a state, wherein the state may be read by an RFID reader, the device, comprising:

a capacitor for storing charge, wherein the charge represents a state;

a diode-connected transistor connected to the capacitor;

a voltage node for coupling to a voltage source, wherein the voltage node is coupled to the diode-connected transistor;

wherein leakage current of the diode-connected transistor determines a rate at which the charge stored in the capacitor dissipates;

wherein a characteristic of the capacitor, the diode-connected transistor, or both, is selected to maintain the charge in the capacitor for a selected time period; and

,

wherein an RFID reader, within the selected time period, can read the charge to determine the state of the RFID tag.

14. The device of claim 13, wherein, the leakage current of the diode-connected transistor conducts in deep subthreshold regime when the voltage source is off.

15. The device of claim 13, wherein the selected time period for which the state is stored is user-defined.

16. A device for temporarily storing a state in a portable data storage circuit, the device comprising:

a capacitor for storing charge;

a high impedance element coupled with the capacitor, between the capacitor and a voltage source;

wherein the device is configured to permit the charge stored in the capacitor to be sensed via a reader wirelessly communicating with the portable data storage circuit;

wherein the high impedance element controls a rate at which the charge stored in the capacitor dissipates;

wherein a characteristic of the capacitor, the high impedance element, or both, is selected to maintain the charge in the capacitor for a selected time period; and

wherein the reader is able to determine the state of the portable data storage circuit when wirelessly communicating with the portable data storage circuit during the selected time period.

17. The device of claim 16,

wherein, the portable data storage unit includes an RFID tag;

wherein, the RFID tag further includes a radio circuit.

18. The device of claim 16, further comprising a switch to disable or enable the capacitor.

19. The device of claim 16, wherein, the RFID tag further includes a controller circuitry to selectively charge or discharge the capacitor.

20. The device of claim 16,

wherein, the rate at which the charge dissipates is user-selectable;

wherein, the user-selectable time period is communicated to the device by an RFID reader.

21. The device of claim 16, wherein, the high impedance element includes, one or more of, a bleeding resistor and a diode.

22. The device of claim 16, wherein, the high impedance element includes a transistor that is electrically trimmed and functions as a constant current source when the voltage source is off.

23. The device of claim 16,

wherein, the high impedance element includes two or more capacitors in parallel;

and,

wherein, the two or more capacitors are controlled by a microcontroller.