Dual frequency radio tag for a radio frequency identification system

• US 20060071756A1
• Filed: 11/09/2005
• Published: 04/06/2006
• Est. Priority Date: 07/20/1999
• Status: Active Grant

• Current Assignee: Axcess International, Inc. (Amphion Innovations PLC)
• Original Assignee: Axcess, Inc.
• Inventors: Steeves, Wayne E.
• Granted Patent: US 7,271,727 B2
• Time in Patent Office: Days
• US Class Current: 340/10.100
• 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: G08B 13/1427 with transmitter-receiver for distance detection
• CPC Class Codes: G08B 13/2462 Asset location systems combined with EAS inventory, tracking, logistic G06Q10/00; entrance control systems G07C9/00

Abstract

A dual frequency radio tag for a radio frequency identification system is provided that includes an antenna system and a first receiver coupled to the antenna system. The first receiver receives and processes request signals from a first unit type at a first frequency. A second receiver is coupled to the antenna system and receives and processes request signals from a second unit type at a disparate second frequency. A transmitter is coupled to the antenna system and transmits response signals from the radio tag at the second frequency.

Claims

1. A radio frequency tag, comprising:

an antenna system;

a first receiver coupled to the antenna system and operable to receive and process request signals from a first unit type at a first frequency;

a second receiver coupled to the antenna system and operable to receive and process request signals from a second unit type at a disparate second frequency; and

a transmitter coupled to the antenna system and operable to transmit response signals at the second frequency.

2. The radio tag of claim 1, wherein the second unit type has a limited power supply and the first frequency is a lower frequency than the second disparate frequency.

3. The radio tag of claim 2, wherein the first frequency is a low frequency (LF).

4. The radio tag of claim 2, wherein the first frequency is a very low frequency (VLF).

5. The radio tag of claim 2, wherein the first frequency is a microwave frequency.

6. The radio tag of claim 2, wherein the second frequency is a very high frequency (VHF).

7. The radio tag of claim 2, wherein the second frequency is an ultra high frequency (UHF).

8. The radio tag of claim 2, wherein the first unit type is a base station and the second unit type is another radio frequency tag.

9. The radio tag of claim 1, further comprising:

a processor coupled to the first receiver, the second receiver, and the transmitter, the processor operable to generate response signals for transmission in response to the request signals received by the first receiver and the second receiver.

10. The radio tag of claim 1, further comprising a local power supply.

11. The radio tag of claim 2, wherein the second receiver comprises:

a local oscillator operable, when active, to generate a demodulated signal by demodulating received traffic;

a detector coupled to the local oscillator to detect communicated signals in the demodulated signal; and

a quench oscillator coupled to the local oscillator and operable to periodically activate the local oscillator for the purpose of detecting the presence of a communicated signal and to continuously activate the local oscillator in response to the presence of the communicated signal for the purpose of collecting the communicated signal.

12. The radio tag of claim 11, wherein the local oscillator is operable to demodulate received traffic at the first frequency and the communicated signal is traffic modulated at the first frequency.

13. The radio tag of claim 11, the quench oscillator comprising:

a first stage quench oscillator coupled to the local oscillator and operable, when active, to activate the local oscillator; and

a second stage quench oscillator coupled to the first stage quench oscillator and operable in a low power mode to periodically activate the first stage quench oscillator in order to periodically activate the local oscillator for the purpose of detecting the presence of the communicated signal and operable in a full power mode to continuously activate the first stage quench oscillator in order to continuously activate the local oscillator for the purpose of collecting the communicated signal.

14. The radio tag of claim 13, further comprising a microcontroller coupled to the detector and the quench oscillator and operable to control the mode of the second stage quench oscillator in response to detection of the communicated signal by the detector.

15. The radio tag of claim 14, wherein the microcontroller is operable to automatically transition the second stage quench oscillator from the low to the full power mode in response to detection of the communicated signal by the detector and to automatically return the second stage quench oscillator from the full to the low power mode following collection of the communicated signal.

16. The radio tag of claim 13, wherein the low power mode has a limited duty cycle.

17. The radio tag of claim 13, wherein the low power mode has a duty cycle of five percent or less.

18. The radio tag of claim 13, wherein the low power mode has a duty cycle of approximately one percent or less.

19. The radio tag of claim 11, wherein the quench oscillator is a dual frequency oscillator having a low power mode to periodically activate the local oscillator for the purpose of detecting the presence of the communicated signal and a full power mode to continuously activate the local oscillator for the purpose of collecting the communicated signal.

20. The radio tag of claim 11, further comprising:

a battery power supply;

a low power mode for the quench oscillator to periodically activate the local oscillator for the purpose of detecting the presence of the communicated signal; and

wherein the low power mode is powered by only leakage current from the battery.

21. The radio tag of claim 20, wherein the leakage current is less than 500 nanoamps.

22. The radio tag of claim 2, wherein the first receiver comprises:

a threshold voltage generator coupled to a local power supply and operable to generate a threshold voltage signal on a threshold voltage generator output; and

a comparator having a first comparator input coupled to the antenna system to accept a received signal and a second comparator input coupled to the threshold voltage generator output to receive the threshold voltage signal, the comparator powered by the local power supply and operable to compare the received signal to the threshold voltage signal and to generate a digital output based on the comparison.

23. The radio tag of claim 22, wherein the comparator and the threshold voltage generator are powered by only leakage current from the local power supply.

24. The radio tag of claim 22, wherein the comparator and the threshold voltage generator are powered by less than four microamps of current from the local power supply.

25. The radio tag of claim 22, wherein a power consumption of the comparator is approximately three microamps or less.

26. The radio tag of claim 22, wherein a power consumption of the threshold voltage generator is less than 1 microamp of current from the local power supply.

27. The radio tag of claim 22, wherein the local power supply is a battery power supply.

28. The radio tag of claim 22, wherein the comparator has a propagation delay of less than fifteen percent of a period of a carrier signal of the second frequency on which communicated signals are received such that at least seven digital outputs are generated for each period.

29. The radio tag of claim 22, wherein the comparator has a propagation delay of approximately ten percent of a period of a carrier signal of the second frequency on which communicated signals are received such that at least ten digital outputs are generated for the received signal during each period.

30. The radio tag of claim 22, wherein the comparator has a propagation delay of less than one microsecond.

31. The radio tag of claim 22, the threshold voltage generator comprising:

a first resistor coupled to the local power supply;

a second resistor coupled in series to the first resistor, the second resistor further coupled to a ground; and

the threshold voltage generator output coupled to a connection between the first resistor and the second resistor.

32. The radio tag of claim 31, further comprising:

a capacitor coupled to the connection between the first resistor and the second resistor, the capacitor further coupled to the ground, the capacitor operable to maintain a substantially constant voltage on the threshold voltage generator output.

33. The radio tag of claim 22, wherein the threshold voltage signal is less than 50 millivolts.

34. The radio tag of claim 22, wherein the threshold voltage signal is less than 500 millivolts.

35. A radio tag, comprising:

an antenna system;

a first receiver coupled to the antenna system and operable to receive and process signals from a first unit type at a first frequency, the first receiver comprising;

a local oscillator operable, when active, to generate a demodulated signal by demodulating received traffic;

a detector coupled to the local oscillator to detect communicated signals in the demodulated signal; and

a quench oscillator coupled to the local oscillator and operable to periodically activate the local oscillator for the purpose of detecting the presence of a communicated signal and to continuously activate the local oscillator in response to the presence of the communicated signal for the purpose of collecting the communicated signal;

a second receiver coupled to the antenna system and operable to receive and process request signals from a second unit type at a disparate second frequency, the second receiver comprising;

a threshold voltage generator coupled to a local power supply and operable to generate a threshold voltage signal on a threshold voltage generator output; and

a comparator having a first comparator input coupled to an antenna to accept a received signal and a second comparator input coupled to the threshold voltage generator output to receive the threshold voltage signal, the comparator powered by the local power supply and operable to compare the received signal to the threshold voltage signal and to generate a digital output based on the comparison;

a transmitter coupled to the antenna system and operable to transmit response signals at the second frequency.

36. The radio tag of claim 35, wherein the second unit type has a limited power supply and the first frequency is a lower frequency than the second disparate frequency.

37. A method for communications in a radio frequency identification system comprising:

transmitting base station messages to portable radio frequency tags at a first frequency; and

transmitting tag messages to the base station at a second disparate frequency.

38. The method of claim 37, further comprising transmitting inter tag messages at the second frequency.

39. The method of claim 37, wherein the first frequency is a lower frequency than the second frequency.

40. The method of claim 37, wherein the first frequency is a very low frequency (VLF) and the second frequency is an ultra high frequency (UHF).