Differential radio frequency identification reader

• US 7,014,103 B2
• Filed: 06/14/2004
• Issued: 03/21/2006
• Est. Priority Date: 06/13/2003
• Status: Active Grant

• Current Assignee: XTec, Incorporated
• Original Assignee: XTec, Incorporated
• Inventors: Fernandez, Alberto J.
• Primary Examiner(s): Frech, Karl D.
• Assistant Examiner(s): WALSH, DANIEL I
• Application Number:
  US10/867,372
• Publication Number:
  US 20050017073A1
• Time in Patent Office: 645 Days
• Field of Search: 340/825.36, 340/7.37, 340/572.1, 340/571.2, 340/5.1, 340/5.2, 340/5.66, 340/5.61, 340/7.97, 340/5.92, 340316-317, 340 101- 106, 340/572.4, 340/10.41, 340/5.64, 340/572.7, 235/382, 235/451, 235/472.02, 235/487, 235/375, 343/895
• US Class Current: 235/375
• 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 7/10316 using at least one antenna particularly designed for interrogating the wireless record carriers antennas in general H01Q1/22
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2431 Tag circuit details
• CPC Class Codes: G08B 13/2471 Antenna signal processing by receiver or emitter
• CPC Class Codes: G08B 13/2477 Antenna or antenna activator circuit

Abstract

Systems and techniques for reading a radio frequency identification transponder are described. A transmit coil produces a transmit field to power and interrogate the transponder. A reference coil and a receive coil furnish inputs to a differential amplifier, balanced so that the differential amplifier produces a predetermined signal. The receive coil senses changes produced by the transponder, while the reference coil is relatively isolated from such changes. The differential amplifier produces an amplified signal based on the difference between the inputs from the receive coil and the reference coil, so that the signal produced by the differential amplifier is based on the field effect changes produced by the transponder.

Claims

1. A differential radio frequency identification reader for producing a signal resulting from effects caused by a radio frequency identification (RFID) tag to be read, comprising:

a transmit coil for emitting a transmit field to power and interrogate a transponder;

a receive coil for sensing changes in the transmit field resulting from effects caused by the RFID tag;

a reference coil effectively isolated from the RFID tag and operating to sense the transmit field unaffected by the RFID tag; and

a differential amplifier for receiving inputs from the receive coil and the reference coil, the differential amplifier being operative to amplify a difference of said inputs thereby producing an amplified output signal reflecting the changes in the transmit field caused by the RFID tag.

2. The reader of claim 1 wherein the RFID tag is a passive tag which communicates by changing a load on the transmit field.

3. The reader of claim 1 wherein the RFID tag is associated with an object or person whose location is to sensed.

4. The reader of claim 1 wherein said reader is integrated in a portable inventory control device having an extended effective read range.

5. The reader of claim 1 further comprising means for communicating with a central control station.

6. The reader of claim 1 further comprising means for adjusting the output of the differential amplifier to substantially zero in the absence of changes in the transmit field caused by the RFID tag.

7. The reader of claim 1 further comprising:

a radio frequency (RF) generator for producing an RF output signal; and

a radio frequency modulator for receiving the RF output signal and for modulating a transmission data signal onto the RF output signal.