RFID tag receive signal strength indicator

• US 7,733,218 B2
• Filed: 03/31/2006
• Issued: 06/08/2010
• Est. Priority Date: 03/31/2006
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Sun, Ming-Hao, Drago, Randall Allen, Hockey, Theodore, White, Joseph
• Primary Examiner(s): Wu; Daniel
• Assistant Examiner(s): Mahase; Pameshanand
• Application Number:
  US11/394,164
• Publication Number:
  US 20070247286A1
• Time in Patent Office: 1,530 Days
• Field of Search: 340/10.4, 340/10.1, 340/825.49, 340/7.21, 340/572.1, 340/572.4
• US Class Current: 340/10.4
• CPC Class Codes: G06K 19/0716 at least one of the integrated circuit chips comprising a sensor or an interface to a sensor
• 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: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 5/48 Transceivers
• CPC Class Codes: H04B 5/77 for interrogation

Abstract

Methods, systems, and apparatuses for detecting a reader signal strength in a radio frequency identification (RFID) tag is described. A tag is configured to monitor an attribute of a reader transmitted signal, such as the signal strength. The tag generates an indication of the signal attribute, and transmits the indication of the signal attribute to the reader.

Claims

1. A method for monitoring a radio frequency identification (RFID) reader communication signal in a RFID tag, comprising:

(a) receiving at the tag a command having a timing parameter to measure a signal strength of a reader communication signal, wherein the timing parameter dictates a time for measuring the signal strength;

(b) measuring a strength of a received radio frequency communication signal from an output signal of a charge pump in the tag; and

(c) transmitting an indication of the strength of the radio frequency communication signal.

2. The method of claim 1, wherein the command is transmitted by a reader according to an EPC Gen 2 communications protocol, wherein the command is a CUSTOM command, wherein step (a) comprises:

receiving at the tag the CUSTOM command.

3. The method of claim 1, wherein step (b) comprises:

converting the received radio frequency communication signal from analog form to a digital representation.

4. The method of claim 3, wherein step (c) comprises:

transmitting the digital representation.

5. The method of claim 1, wherein step (b) comprises:

receiving the radio frequency communication signal;

converting the received radio frequency communication signal to a direct current (DC) voltage signal;

comparing the DC voltage signal to a plurality of different reference DC voltages to generate an indication of a strength of the received radio frequency communication signal.

6. The method of claim 5, wherein step (b) further comprises:

encoding the generated indication.

7. The method of claim 6, wherein step (c) comprises:

transmitting the encoded indication.

8. The method of claim 1, wherein step (b) comprises:

receiving the radio frequency communication signal;

converting the received radio frequency communication signal to a direct current (DC) voltage signal;

generating a plurality of sealed versions of the DC voltage signal; and

comparing the plurality of scaled versions of the DC voltage signal to a reference DC voltage to generate a indication of a strength of the received radio frequency communication signal.

9. The method of claim 1, wherein step (b) comprises:

receiving the radio frequency communication signal;

converting the received radio frequency communication signal to a direct current voltage signal; and

generating the indication of the strength of the received radio frequency communication signal by measuring an amplitude of the direct current voltage signal.

10. A system for monitoring a radio frequency identification (RFID) reader communication signal in a RFID tag, comprising:

means for receiving at the tag a command, having a timing parameter, to measure a signal strength of a reader communication signal, wherein the timing parameter dictates a time for measuring the signal strength;

means for measuring a strength of a received radio frequency communication signal from an output signal of a charge pump in the tag; and

means for transmitting an indication of the strength of the radio frequency communication signal.

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

an antenna to receive a command, having a timing parameter, to measure a strength of a radio frequency communication signal, wherein the timing parameter dictates a time for measuring the signal strength; and

a signal strength monitor module configured to measure the strength of the radio frequency communication signal received by the antenna from an output signal of a charge pump in the tag;

wherein the signal strength monitor module is further configured to generate an indication of the measured strength of the radio frequency communication signal.

12. The RFID tag of claim 11, further comprising:

a modulator coupled to the antenna;

wherein the modulator is configured to modulate the indication of the strength of the radio frequency communication signal onto a radio frequency signal.

13. The RFID tag of claim 11, further comprising:

a demodulator coupled to the antenna;

wherein the demodulator is configured to demodulate a radio frequency signal received by the antenna to recover a command to measure the signal strength of a reader communication signal.

14. The RFID tag of claim 13, wherein the command is received according to an EPC Gen 2 communications protocol, wherein the command is a CUSTOM command.

15. The RFID tag of claim 11, further comprising:

a substrate; and

an integrated circuit (IC) die mounted to the substrate, wherein the signal strength monitor module is in the IC die;

wherein the antenna is formed on the substrate.

16. The RFID tag of claim 11, further comprising:

a charge pump that generates a direct current (DC) voltage signal from the received radio frequency communications signal.

17. The RFID tag of claim 16, wherein the signal strength monitor module comprises:

an analog-to-digital (A/D) converter configured to convert the DC voltage signal from analog form to a digital representation.

18. The RFID tag of claim 17, further comprising:

a modulator coupled to the antenna, wherein the modulator is configured to modulate a radio frequency signal with the digital representation.

19. The RFID tag of claim 16, wherein the signal strength monitor module comprises:

a plurality of comparators, wherein each comparator of the plurality of comparators is configured to compare a corresponding scaled version of the DC voltage signal to a reference voltage, wherein the plurality of comparators collectively output a digital representation of an amplitude of the DC voltage.

20. The RFID tag of claim 19, wherein the signal strength monitor module further comprises:

an encoder configured to encode the digital representation.

21. The RFID tag of claim 20, further comprising:

a modulator coupled to the antenna, wherein the modulator is configured to modulate a radio frequency signal with the encoded digital representation.

22. A method in a radio frequency identification (RFID) reader for monitoring transmitted signal strength, comprising:

(a) transmitting to a tag a command, having a timing parameter, to measure a signal strength of a reader communication signal, wherein the timing parameter dictates a time for measuring the signal strength;

(b) transmitting the reader communication signal; and

(c) receiving from the tag an indication of the strength of the transmitted radio frequency communication signal from an output signal of a charge pump in the tag.

23. The method of claim 22, wherein the command is a CUSTOM command of the EPC Gen 2 communications protocol, wherein step (a) comprises:

transmitting the CUSTOM command.

24. A system in a radio frequency identification (RFID) reader communication for monitoring transmitted signal strength, comprising:

means for transmitting to a tag a command, having a timing parameter, to measure a signal strength of a reader communication signal, wherein the timing parameter dictates a time for measuring the signal strength; and

means for receiving from the tag an indication of the strength of a transmitted radio frequency communication signal from an output signal of a charge pump in the tag.