Battery Assisted Tag and RFID System

• US 20100060432A1
• Filed: 02/11/2009
• Published: 03/11/2010
• Est. Priority Date: 09/05/2008
• Status: Active Grant

• Current Assignee: Zest Labs, Inc.
• Original Assignee: Intelleflex Corporation
• Inventors: Dacus, Farron, van Niekerk, Johannes Albertus, Rodriguez, Alfonso
• Granted Patent: US 8,581,704 B2
• Time in Patent Office: Days
• US Class Current: 340/10.300
• 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
• 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
• CPC Class Codes: G06K 7/10019 resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08
• CPC Class Codes: H04Q 2213/13095 PIN / Access code, authentication

Abstract

Embodiments of the present invention provide for RFID systems that employ a plurality of battery assisted semi-passive and semi-active RFID tags with optimized system operation. The RFID tags feature receivers operating with multiple dynamic range states with square law mode for improved sensitivity, and part time active transmit in the tag to supplement its backscatter transmitter and thus support system operation taking full advantage of the sensitivity of the tag. In certain embodiments of the invention, tag sensitivity and reliability are further enhanced by the use pseudo-random sequence based receiver training and frame synchronizing.

Claims

1. An RFID system comprising:

an RFID reader that activates an RFID tag, the RFID reader comprising;

a bit sequence generator that generates a pseudo-random bit sequence that functions as a frame synchronization flag;

an activation command generator that prepends an activation command with the frame synchronization flag;

a transmitter that sends the frame synchronization flag and the activation command to the RFID tag; and

at least one RFID tag comprising a hibernate control module that determines a validity of the frame synchronization flag using a pseudo-random sequence correlator.

2. The system of claim 1 wherein the frame synchronization flag also functions as an activation flag.

3. The system of claim 2 wherein the activation flag provides tag power-up sequencing prior to an RFID reader transmitting the activation command.

4. The system of claim 1 further wherein the RFID reader prepends the frame synchronization flag with a continuous wave carrier that provides a sample signal on which the at least one RFID tag conducts receiver training.

5. The system of claim 1 wherein the RFID reader prepends the frame synchronization flag with an additional pseudo-random bit sequence that provides a sample signal upon which the at least one RFID tag conducts receiver training.

6. The system of claim 5 wherein the frame synchronization flag and the additional pseudo-random bit sequence are prepended with a continuous wave carrier pattern to provide an additional sample signal upon which the at least one RFID tag conducts receiver training.

7. The system of claim 6 wherein the additional pseudo-random bit sequence provides tag power-up sequencing prior to the RFID reader transmitting the activation command.

8. The system of claim 5 further comprising a dynamic range selection module, coupled within the at least one RFID tag, the dynamic range selection module utilizes at least a portion of the prepended pseudo-random bit sequence to select a tag receiver dynamic range state in which to conduct communications.

9. The system of claim 1 further comprising a linear feedback shift register circuit, coupled within the at least one RFID tag, the linear feedback shift register circuit synthesizes a bit sequence within the frame synchronization flag utilizing a plurality of register elements.

10. The system of claim 1 wherein the RFID reader controls a frame synchronization flag correlation threshold adaptation.

11. The system of claim 10 further comprising a settings file, stored within a memory in the at least one RFID tag, the settings file contains the correlation threshold that is communicated to the at least one RFID tag by the RFID reader.

12. The system of claim 11 wherein the at least one RFID tag internally alters the correlation threshold where a valid correlation is defined to occur.

13. The system of claim 1 wherein the at least one RFID tag performs the steps comprising of:

transitioning from a low power hibernate mode into a high power mode upon receiving and performing a first correlation of a first portion of the frame synchronization flag, whereby the first correlation is at least as large as a minimum first threshold;

checking a second correlation of a second portion of the frame synchronization flag; and

operating within a particular power mode based on the first and second correlations.

14. An RFID tag comprising:

a battery, coupled within the RFID tag, that allows the RFID tag to operate in an active mode;

a square law detector, coupled within the RFID tag, that allows the RFID tag to operate in a square law mode;

a sensitivity control, coupled within the RFID tag, that performs a training operation using a symbol-based forward link training sequence during hibernation of the RFID tag, the symbol-based forward link training sequence being sufficiently long to allow linear methods of low power and accurate slicer reference acquisition for Pulse Interval Encoding (PIE) demodulation; and

wherein the acquired slicer reference is used during a subsequent activation command.

15. The RFID tag of claim 14 wherein the slicer reference acquired and adapted during an RFID tag hibernation mode is saved and used as an initial slicer reference in a subsequent normal mode.

16. The RFID tag of claim 15 wherein reference tracking is initiated during a remainder of RFID reader transmitted commands and data.

17. An RFID reader activation command generator comprising:

a pseudo-random bit sequence generator, coupled within the RFID reader activation command generator, the pseudo-random bit sequence generator generates a pseudo-random bit sequence that functions as a frame synchronization flag;

an activation command assembler, coupled to the pseudo-random bit sequence generator, the activation command assembler inserts the frame synchronization flag within a preamble of the activation command and inserts a stuffing bit within the activation command such that the activation command is prevented from deterministically emulating a frame synchronization flag utilized in normal mode communications; and

wherein a value of the stuffing bit is selected to mismatch a similarly positioned bit in a normal command frame synchronization flag.

18. An RFID reader activation command generator comprising:

a pseudo-random bit sequence generator, coupled within the RFID reader activation command generator, the pseudo-random bit sequence generator generates a pseudo-random bit sequence that functions as a frame synchronization flag;

an activation command assembler, coupled to the pseudo-random bit sequence generator, the activation command assembler inserts the frame synchronization flag within a preamble of the activation command and inserts a stuffing bit within the activation command such that the activation command is prevented from deterministically emulating a frame synchronization flag utilized in activation mode communications; and

wherein a value of the stuffing bit is selected to mismatch a similarly positioned bit in an activation command frame synchronization flag.

19. An RFID reader normal mode command generator comprising:

a pseudo-random bit sequence generator, coupled within the RFID reader normal mode command generator, the pseudo-random bit sequence generator generates a pseudo-random bit sequence that functions as a frame synchronization flag;

a normal mode command assembler, coupled to the pseudo-random bit sequence generator, the normal mode command assembler inserts the frame synchronization flag within a preamble of the normal mode command and inserts a stuffing bit within the normal mode command and data such that the normal mode command and data are prevented from deterministically emulating a frame synchronization flag utilized in activation mode communications; and

wherein a value of the stuffing bit is selected to mismatch a similarly positioned bit in an activation frame synchronization flag.

20. An RFID reader normal mode command generator comprising:

a pseudo-random bit sequence generator, coupled within the RFID reader normal mode command generator, the pseudo-random bit sequence generator generates a pseudo-random bit sequence that functions as a frame synchronization flag;

a normal mode command assembler, coupled to the pseudo-random bit sequence generator, the normal mode command assembler inserts the frame synchronization flag within a preamble of the normal mode command and inserts a stuffing bit within the normal mode command and data such that the normal mode command and data are prevented from deterministically emulating a frame synchronization flag utilized in normal mode communications; and

wherein a value of the stuffing bit is selected to mismatch a similarly positioned bit in a normal frame synchronization flag.

21. An RFID system comprising:

an RFID reader;

at least one RFID tag comprising;

a receiver, coupled to receive an input RF signal from the RFID reader, the receiver including a biased transistor detector that harvests a current from the RF signal; and

and wherein the at least one RFID tag is operable within a plurality of dynamic range modes corresponding to a plurality of dynamic range states, and at least one mode within the plurality of dynamic range modes being a square law mode.

22. The system of claim 21 wherein the biased transistor detector is a MOS transistor that operates in weak inversion during the square law mode.

23. The system of claim 21 wherein the receiver further comprises a switchable RF amplifier that operates relative to a selected mode within the plurality of modes.

24. The system of claim 21 wherein the receiver further comprises automatic gain control that controls a gain applied to the harvested current.

25. The system of claim 21 wherein the receiver further comprises automatic gain control that controls a continuous RF attenuator.

26. The system of claim 21 wherein the receiver further comprises automatic gain control that controls a continuous RF amplifier.

27. The system of claim 21 wherein the receiver further comprises an impedance up-conversion that increases sensitivity of the biased transistor detector.

28. The system of claim 21 wherein the receiver further comprises a low noise amplifier that increases sensitivity of the biased transistor detector.

29. The system of claim 21 wherein the at least one RFID tag further comprises an active transmitter that transmits within a first power range.

30. The system of claim of claim 29 wherein the at least one RFID tag further comprises a backscatter transmitter that transmits within a second power range.

31. The system of claim 30 wherein the RFID reader selects either the active transmitter or the backscatter transmitter as being the transmitter to be used on the at least one RFID tag for a period of time.

32. The system of claim 30 wherein the at least one RFID tag selects either the active transmitter or the backscatter transmitter as being the transmitter to be used on the at least one RFID tag for a period of time.