Wide band RFID system with tag on flexible label

• US 20070152833A1
• Filed: 12/28/2005
• Published: 07/05/2007
• Est. Priority Date: 12/28/2005
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: SandLinks Ltd.
• Inventors: Kaplan, Gideon, Raphaeli, Dan
• Granted Patent: US 7,504,952 B2
• Time in Patent Office: Days
• US Class Current: 340/572.800
• CPC Class Codes: G06K 19/0702 the arrangement including a battery
• 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 19/07786 the antenna being of the HF type, such as a dipole

Abstract

An active radio frequency identification (RFID) tag implemented on a flat label. The tag includes a battery printed on the label, a flat wide-band antenna printed on the label and a wide band communication circuit implemented as a chip inlay inside the label. The circuit is attached to the battery and to the antenna. The combined thickness of the battery, the antenna and the circuit as printed on the flexible label is less than one millimeter. The battery, the antenna and the circuit are printed on the label so as to render substantial flexibility to the RFID tag. The circuit operates at a center frequency of at least one gigahertz and a bandwidth at least twenty percent of said center frequency or a bandwidth at least 500 Mhz. The tag typically includes an inaccurate clock source such as an RC circuit and does not include a crystal. Average power consumption of the battery is preferably reduced by operating the tag with a low duty ratio between an active and an inactive interval; and during the active interval transmitting in bursts while turning off parts of the tag between the bursts. The communications circuit performs timing measurements on incoming received waveforms and transmits transmit signals in response to the received waveforms with timing based on the timing measurements. The receiver circuitry locks on a repetition frequency of the incoming received waveforms, and based on the repetition frequency generates a pulse repetition frequency of the transmit signals.

Claims

1. An active radio frequency identification (RFID) tag implemented on a flat label, the tag comprising:

(a) a battery printed on the label;

(b) a flat antenna printed on the label; and

(c) a communications circuit as an inlay on the label, wherein said circuit is operatively attached to said battery and to said antenna.

2. The tag, according to claim 1, wherein said communications circuit includes a wide-band communications circuit.

3. The tag, according to claim 1, wherein a combined thickness of said battery, said antenna and said circuit on the flat label is less than one millimeter.

4. The tag, according to claim 1, wherein said circuit operates at a bandwidth at least twenty percent of said center frequency.

5. The tag, according to claim 1, wherein said circuit operates at a center frequency of at least 1 gigahertz and a bandwidth of at least 500 Mhz.

6. The tag, according to claim 1, wherein said battery, said antenna and said circuit are printed on the flat label so as to render substantial flexibility to the RFID tag.

7. The tag, according to claim 1, wherein said communications circuit includes receiver and transmitter circuitry.

8. The tag, according to claim 1, further comprising:

(d) an inaccurate clock source operatively attached to said circuit.

9. The tag, according to claim 8, wherein said inaccurate clock source does not include a crystal.

10. The tag, according to claim 8, wherein said inaccurate clock source is based on a combination of a resistor and a capacitor.

11. The tag, according to claim 8, wherein average power consumption of said battery is reduced by operating with a low duty ratio between an active and an inactive interval;

and during said active interval said communications circuit communicates in bursts while turning off at least a portion of the tag for at least a portion of an interval between said bursts.

12. The tag, according to claim 1, wherein said communications circuit includes receiver and transmitter circuitry, the tag further comprising:

(d) an inaccurate clock source operatively attached to said communications circuit. wherein said communications circuit performs timing measurements on incoming received waveforms and transmits transmit signals in response to said received waveforms with timing based on said timing measurements.

13. The tag, according to claim 12, wherein said receiver circuitry locks on a repetition frequency of said incoming received waveforms, and based on said repetition frequency generates a pulse repetition frequency of said transmit signals.

14. The tag, according to claim 1, wherein said circuit includes an ultra wide band transceiver circuit wherein said transceiver circuit includes an inaccurate frequency reference, wherein said transceiver circuit estimates a received center frequency of a received waveform and based on said received center frequency said transceiver circuit transmits an ultra wide band pulsed waveform with a locked transmit center frequency based on said received center frequency.

15. The tag, according to claim 1, wherein said circuit includes a transceiver circuit wherein said transceiver circuit includes an inaccurate frequency reference, wherein said transceiver circuit estimates a received center frequency of a received waveform and said transceiver circuit locks a timing of a transmitted signal based on said received center frequency.

16. The tag, according to claim 1, wherein said circuit does not include an accurate frequency source.

17. A method of communicating in a communication system, the system including a reader and a tag as an inlay on a label, wherein the tag includes an inaccurate clock source, the method comprising the steps of:

(a) transmitting by the tag a transmission based on the inaccurate clock source;

(b) receiving by the reader said transmission; and

(c) the reader upon synchronizing on a center frequency and a pulse repetition frequency of said transmission, attempting to demodulate data included in said transmission.

18. The method, according to claim 17, wherein said transmission is a wide band transmission.

19. The method, according to claim 17, further comprising the steps of

(d) operating of the tag with a low duty ratio between an active and an inactive interval, and

(e) during said active interval, communicating in bursts while turning off at least a portion of the tag for at least a portion of an interval between said bursts.

20. The method, according to claim 17, further comprising the steps of:

(d) upon said synchronizing, compensating for the inaccurate clock source

(e) sending a message to said tag including a result based on said compensating; and

(f) retransmitting by said tag another transmission based on said message, thereby improving synchronization of said tag.

21. The method, according to claim 20, further comprising the steps of:

(g) correcting by the tag a center frequency and timing of said retransmitting; and

(h) exchanging further data between the tag and the reader based on said center frequency and said timing.

22. The method, according to claim 17, further comprising the step of, prior to said transmitting:

(d) first transmitting by the reader a first ultra-wide-band transmission, wherein said transmitting by the tag is in response to said first transmitting by the reader.

23. The method, according to claim 22, further comprising the step of:

(e) measuring a time delay between said first ultra-wide-band transmission and said receiving thereby determining a distance to the tag

24. The method, according to claim 22, wherein said first ultra-wide-band transmission includes a packet including a plurality of symbols, wherein a format of said packet includes a preamble, data, and a postamble, wherein at least one said symbol includes a short pulse sequence followed by an inactive time period for the remainder of said symbol, wherein said first ultra-wide-band transmission has a duration at least until said receiving is complete.

25. A method which reduces average power consumption of a battery powering a device, wherein the battery and the device are printed on a label, the method includes the steps of:

(a) operating the device with a low duty ratio between an active and an inactive interval; and

(b) during said active interval, communicating in bursts while turning off at least a portion of the device for at least a portion of an interval between said bursts.

26. A communications system comprising:

(a) a tag including a battery printed on the label, a flat antenna printed on said label, and a communications circuit as an inlay on said label, wherein said circuit is operatively attached to said battery and to said antenna;

(b) a reader in communication with said tag, wherein said reader upon synchronizing on a center frequency and a pulse repetition frequency of a transmission from said tag, said reader attempts to demodulate data included in said transmission.

27. The system, according to claim 26, wherein said tag further includes an inaccurate frequency source, and wherein said tag does not include an accurate frequency source.