Method, system, and apparatus for communicating with a RFID tag population

• US 7,057,511 B2
• Filed: 02/12/2002
• Issued: 06/06/2006
• Est. Priority Date: 02/12/2001
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Bandy, William R., Powell, Kevin J., Shanks, Wayne E., Arneson, Michael R.
• Primary Examiner(s): La, Anh V.
• Application Number:
  US10/073,000
• Publication Number:
  US 20020149483A1
• Time in Patent Office: 1,575 Days
• Field of Search: 340/572.1, 340/572.7, 340/572.8, 340/572.4, 340/10.1, 340/5.8, 340/572.5, 340/573.1, 340/541, 340/538, 340/531, 340/10.3, 340/10.4, 340/10.32, 340/825.49, 235/439, 235/435
• US Class Current: 340/572.1
• CPC Class Codes: G06K 17/00 Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations
• CPC Class Codes: G06K 19/0713 the arrangement including a power charge pump
• 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 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 19/07767 the first and second communication means being two different antennas types, e.g. dipole and coil type, or two antennas of the same kind but operating at different frequencies
• 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 7/10039 interrogator driven, i.e. synchronous
• CPC Class Codes: G06K 7/10069 the collision being resolved in the frequency domain, e.g. by hopping from one frequency to the other frequency hopping or spread spectrum techniques H04B7/00
• CPC Class Codes: G06K 7/10108 interrogating only those RFIDs that fulfill a predetermined requirement, e.g. selecting all RFIDs having the same speed and moving in a cloud like fashion, e.g. on the same train; interrogating only RFIDs having a certain predetermined temperature, e.g. in the same fridge, another possibility being the active ignoring of a group of tags that fulfill a predetermined requirement, equivalent to the Boolean NOT operation
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: G08B 13/2485 Simultaneous detection of multiple EAS tags
• CPC Class Codes: G11C 5/142 Contactless power supplies, e.g. RF, induction, or IR
• CPC Class Codes: H04L 7/0331 with a digital phase-locked loop [PLL] processing binary samples, e.g. add/subtract logic for correction of receiver clock H04L7/0337 takes precedence

Abstract

A method, system, and apparatus for communicating with a radio frequency identification (RFID) tag population that includes one or more tags are described. The tags are interrogated by a reader which may be located in a network of readers. The reader interrogates the tags by transmitting data symbols to the tags. Tags respond to the reader with backscatter symbols. Bit patterns, such as identification numbers stored in the tags, are collected from the plurality of tags without collisions. Collisions are avoided because the backscatter symbols transmitted by the tags use different characteristics to represent different data bits. For example, a first backscatter symbol frequency is used by the tag to represent a “0” bit, and a second backscatter symbol frequency is used by the tag to represent a “1” bit.

Claims

1. A radio frequency identification (RFID) tag device, comprising:

an antenna that receives an electromagnetic carrier signal;

a receiver coupled to said antenna, wherein said receiver is configured to receive a symbol from said antenna, and

a modulator coupled to said antenna;

wherein said modulator is configured to receive a response value, and is configured to select one of a plurality of frequencies according to said response value to be a selected frequency signal;

wherein said modulator is configured to backscatter modulate said received symbol according to said selected frequency signal to produce a backscatter modulated symbol; and

wherein said antenna is configured to transmit said backscatter modulated symbol.

2. The tag device of claim 1, wherein said modulator is configured to amplitude modulate said received symbol according to said selected frequency signal to produce said backscatter modulated symbol.

3. The tag device of claim 1, wherein said antenna is configured to receive a RF carrier signal, wherein said receiver is configured to demodulate said received RF carrier signal to said received symbol.

4. The tag device of claim 1, wherein said modulator is configured to select a first frequency for the selected frequency signal if said response value is a first predetermined value, and is configured to select a second frequency for the selected frequency signal if said response value is a second predetermined value;

wherein said transmitted backscatter modulated symbol is a first backscatter modulated symbol when said modulator selects said first frequency, and said transmitted backscatter modulated symbol is a second backscatter modulated symbol when said modulator selects said second frequency.

5. The tag device of claim 1, wherein said received symbol includes a logic low portion followed by a logic high portion, wherein said modulator is configured to modulate said logic high portion of said received symbol according to said selected frequency signal to produce said backscatter modulated symbol.

6. The tag device of claim 1, wherein said modulator includes a switch.

7. The tag device of claim 6, wherein said switch is a single pole, single throw (SPST) switch.

8. The tag device of claim 6, wherein said switch is configured to modulate the received symbol by varying the return loss of said antenna according to said selected frequency signal.

9. The tag device of claim 8, wherein said switch is configured to vary the return loss of said antenna by coupling the antenna to a voltage level when the switch is on that is not equal to the RF voltage level at the antenna when the switch is off.

10. The tag device of claim 1, further comprising:

a state machine that is configured to receive said received symbol and generate said response value, wherein said response value is one of a first predetermined value and a second predetermined value.

11. The tag device of claim 10, further comprising:

a data programming unit that is configured to store a tag identification number;

wherein said state machine is coupled to said data programming unit.

12. The tag device of claim 1, further comprising:

an oscillator that is configured to generate an oscillator frequency;

wherein each of said plurality of frequencies is generated from said oscillator frequency.

13. The tag device of claim 12, wherein said oscillator frequency is greater than 1 MHz.

14. The tag device of claim 1, further comprising:

an oscillator corresponding to each of said plurality of frequencies;

wherein each of said plurality of frequencies is generated by said corresponding oscillator.

15. The tag device of claim 1, further comprising:

an oscillator configured to generate an oscillator frequency; and

a plurality of frequency dividers configured to each receive said oscillator frequency;

wherein each of said plurality of frequencies is output by a respective one of said plurality of frequency dividers.

16. A reader that communicates with a radio frequency identification (RFID) tag device, comprising:

a transmitter that transmits a radio frequency carrier signal modulated with a data symbol;

a receiver that receives at least one backscatter symbol related to the transmitted data symbol; and

a logic module that determines at least one backscatter frequency of said at least one backscatter symbol, wherein said logic module determines that said at least one backscatter symbol represents a first data value when said at least one backscatter frequency includes a first frequency, and determines that said at least one backscatter symbol represents a second data value when said at least one backscatter frequency is determined to include a second frequency.

17. The reader of claim 16, wherein said first data value is a “

0”

bit, and said second data value is a “

1”

bit.

18. The reader of claim 16, wherein said first frequency is equal to 2.5 MHz, and said second frequency is equal to 3.75 MHz.