Battery assisted RFID tag with square-law receiver and optional part time active behavior

• US 9,367,711 B1
• Filed: 09/04/2008
• Issued: 06/14/2016
• Est. Priority Date: 09/04/2008
• Status: Active Grant

• Current Assignee: Zest Labs, Inc.
• Original Assignee: Intelleflex Corporation
• Inventors: Bouchez, Joseph, Dacus, Farron, van Niekerk, Johannes Albertus, Rodriguez, Alfonso
• Primary Examiner(s): McNally, Kerri
• Application Number:
  US12/204,774
• Time in Patent Office: 2,840 Days
• Field of Search: 340 101- 106, 3405721-5729, 235375-385
• US Class Current: 1/1
• CPC Class Codes: G06K 19/0702 the arrangement including a battery
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Abstract

Embodiments of the present invention provide RFID systems having battery-assisted, Semi-Passive RFID tags that operate with sensitive transistor based square law tag receivers utilizing a plurality of tag receiver dynamic range states. Embodiments of the present invention are also enhanced with receiver training and synchronizing methods suited to the high tag sensitivity and need for dynamic range state switching. These enhancements may employ pseudo-random sequence based receiver training, activation signaling, and frame synchronizing. Further enhancement is achieved via design of system command sets and tag state machine behavior that control system interference and allow maximum usage of high sensitivity. Command set design also allows for convenient expansion to active transmitters and receivers in tags operating within the same system. Additional enhancement attained via power leveling methods that optimize the amount of transmitted power and interference from a reader in relation to the sensitivity of the RFID tags, their ranges from the reader, and the unique physics of the backscatter RFID radio link.

Claims

1. A method for operating a battery assisted tag within an RFID system, the method comprising:

monitoring at least one characteristic of a detected RF signal at a receiver within the battery assisted tag;

in response to determining the at least one characteristic satisfies a first criteria, operating the battery assisted tag within a first dynamic range state during which battery power is provided to circuitry within the battery assisted tag; and

in response to the at least one characteristic satisfying a second criteria, operating the battery assisted tag within a second dynamic range state during which the battery assisted tag functions in a square law mode, and

wherein the at least one characteristic comprises one or more of a power level of the detected RF signal and a signal-to-noise ratio of the detected RF signal.

2. The method of claim 1 further comprising the step of amplifying the detected RF signal using a current mirror within the receiver.

3. The method as recited in claim 1, wherein operating the battery assisted tag within the first dynamic range state comprises performing Manchester demodulation.

4. The method as recited in claim 1, wherein operating the battery assisted tag within the second dynamic range state comprises performing Pulse Interval Encoding demodulation.

5. The method as recited in claim 4, wherein operating the battery assisted tag within the second dynamic range state further comprises performing Manchester demodulation.

6. The method as recited in claim 1, further comprising duty-cycling the receiver.

7. The method as recited in claim 1, further comprising duty-cycling a part-time active receiver of the tag.

8. The method as recited in claim 7, wherein the duty-cycling is performed when the tag is in a hibernate mode.

9. The method as recited in claim 1, further comprising programming a sensitivity level of the receiver.

10. The method as recited in claim 1, further comprising transitioning from the first dynamic range to the second dynamic range within a common overlap range shared by the first dynamic range and the second dynamic range.

11. The method as recited in claim 10, wherein the common overlap range partially overlaps each of the first dynamic range state and the second dynamic range state.

12. The method as recited in claim 1, comprising operating the receiver in a plurality of dynamic range states comprising the first dynamic range state and the second dynamic range state.

13. The method as recited in claim 1, further comprising extending a range of at least one of the first dynamic range state and the second dynamic range state using compression.

14. The method as recited in claim 1, further comprising:

harvesting current from the detected RF signal using a biased transistor detector of the tag, the biased transistor detector being coupled to receive an input RF signal; and

applying a gain to the harvested current using a mirror within the tag, the mirror being coupled to receive the harvested current.

15. The method as recited in claim 14, further comprising:

passing the gained harvested current through an active load; and

generating a corresponding voltage in response to passing the gained harvested current through the active load.

16. The method as recited in claim 15, further comprising setting an average output voltage for the corresponding voltage using a negative feedback control coupled to the active load.

17. The method as recited in claim 16, further comprising expanding a dynamic range of an output stage comprising the active load using a current control range of the negative feedback control.

18. The method as recited in claim 1, further comprising adjusting a frequency range of an adjustable front end RF filter in relation to a regulatory region in which the tag operates.

19. The method as recited in claim 1, further comprising adjusting a frequency range of an adjustable front end RF filter in relation to a data provided by a RFID reader.

20. The method as recited in claim 1, further comprising receiving an input RF signal using an adjustable front end RF filter of the tag.

21. The method as recited in claim 1, further comprising increasing a sensitivity of the tag using an RF impedance up-conversion coupled to an input of a biased transistor detector of the tag.

22. The method as recited in claim 21, the biased transistor detector comprising a MOS transistor.

23. The method as recited in claim 22, further comprising operating the MOS transistor in a weak inversion mode during a first time period corresponding to a first data rate.

24. The method as recited in claim 1, wherein the at least one characteristic satisfying the second criteria comprises determining at least one signal characteristic on the receiver is operating in the square law mode.

25. The method as recited in claim 1, further comprising:

duty-cycling the receiver;

duty-cycling a part-time active receiver of the tag when the tag is in a hibernate mode;

programming a sensitivity level of the receiver;

transitioning from the first dynamic range to the second dynamic range within a common overlap range shared by the first dynamic range and the second dynamic range, wherein the common overlap range partially overlaps each of the first dynamic range state and the second dynamic range state;

operating the receiver in a plurality of dynamic range states comprising the first dynamic range state and the second dynamic range state;

extending a range of at least one of the first dynamic range state and the second dynamic range state using compression;

harvesting current from the detected RF signal using a biased transistor detector of the tag, the biased transistor detector being coupled to receive an input RF signal;

applying a gain to the harvested current using a mirror within the tag, the mirror being coupled to receive the harvested current

passing the gained harvested current through an active load;

generating a corresponding voltage in response to passing the gained harvested current through the active load;

setting an average output voltage for the corresponding voltage using a negative feedback control coupled to the active load;

expanding a dynamic range of an output stage comprising the active load using a current control range of the negative feedback control;

adjusting a frequency range of an adjustable front end RF filter in relation to either;

a regulatory region in which the tag operates;

or data provided by a RFID reader

receiving the input RF signal using an adjustable front end RF filter of the tag;

increasing a sensitivity of the tag using an RF impedance up-conversion coupled to an input of the biased transistor detector;

operating the biased transistor in a weak inversion mode during a first time period corresponding to a first data rate

wherein the at least one characteristic satisfying the second criteria comprises determining at least one signal characteristic on the receiver is operating in the square law mode;

wherein operating the battery assisted tag within the first dynamic range state comprises performing Manchester demodulation; and

wherein operating the battery assisted tag within the second dynamic range state comprises performing Pulse Interval Encoding demodulation and Manchester demodulation.

26. A battery assisted RFID tag comprising a transistor-based detector, the transistor-based detector comprising:

a bipolar transistor coupled to harvest current from an input RF signal;

an impedance up-conversion circuit coupled to a base of the bipolar transistor;

a compression circuit coupled to a collector of the bipolar transistor;

a current mirror coupled to the compression circuit;

a load coupled to a collector of the current mirror; and

an integrator control system coupled to the load.

27. The battery-assisted RFID tag as recited in claim 26, wherein the load comprises an active load.

28. The battery-assisted RFID tag as recited in claim 26, wherein the load comprises a resistive load.

29. The battery-assisted RFID tag as recited in claim 26, wherein the integrator control system comprises a differential analog integrator circuit.

30. The battery-assisted RFID tag as recited in claim 26, wherein the integrator control system comprises a digital control system.

31. The battery-assisted RFID tag as recited in claim 26, the bipolar transistor comprising a base emitter diode.

32. The battery-assisted RFID tag as recited in claim 26, the bipolar transistor comprising a self-impedance in a base-emitter junction of the bipolar transistor.

33. The battery-assisted RFID tag as recited in claim 26, further comprising a source impedance coupled to the impedance up-conversion circuit.

34. A battery assisted RFID tag comprising:

a receiver coupled to receive input signal from an RFID reader, the receiver comprising;

a biased transistor detector coupled to harvest a detected current from the input signal;

a mirror coupled to receive the harvested current and apply a gain to the harvested current; and

a negative feedback control system coupled to an output of the biased transistor detector; and

an adjustable front end RF filter coupled to receive the input signal.

35. The battery assisted RFID tag as recited in claim 34, further comprising an active load coupled to receive the gained current.

36. The battery assisted RFID tag as recited in claim 34, further comprising a resistive load coupled to receive the gained current.

37. The battery assisted RFID tag as recited in claim 34, further comprising a backscatter transmitter.

38. The battery assisted RFID tag as recited in claim 34, further comprising a part time active transmitter.

39. The battery assisted RFID tag as recited in claim 34, further comprising a part time active receiver coupled to receive the input signal.

40. The battery assisted RFID as recited in claim 34, further comprising:

a switchable RF attenuator;

an RF low noise amplifier;

an RF impedance up-converter coupled to an input of the biased transistor detector;

an active load coupled to receive the gained current;

a backscatter transmitter;

a part time active transmitter;

a part time active receiver coupled to receive the input signal; and

an adjustable front end RF filter coupled to receive the input signal.