Optical interface between receiver and tag response signal analyzer in RFID system for detecting low power resonant tags

• US 5,959,531 A
• Filed: 07/24/1998
• Issued: 09/28/1999
• Est. Priority Date: 07/24/1998
• Status: Expired due to Term

• Current Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated), Mitsubishi Materials Corporation
• Original Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Inventors: Gallagher, William F. III, Barber, Russell E.
• Primary Examiner(s): Swann, Glenn
• Application Number:
  US09/122,121
• Time in Patent Office: 431 Days
• Field of Search: 340/572.1, 340/572.5, 340/531, 359/173, 359/109
• US Class Current: 340/572.1
• 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 7/10346 the antenna being of the far field type, e.g. HF types or dipoles
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2471 Antenna signal processing by receiver or emitter
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22
• CPC Class Codes: G08B 13/2477 Antenna or antenna activator circuit
• CPC Class Codes: G08B 13/2488 Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver
• CPC Class Codes: H04B 10/25758 between a central unit and a single remote unit by means of an optical fibre

Abstract

Noise reduction schemes are provided in a radio frequency identification (RFID) system for use with RFID intelligent tags. Fiber optics are used to communicate analog tag response signals from the output of the receiver circuit to the input of a tag response signal analyzing module, which includes a digital signal processor (DSP). The fiber optics creates electrical isolation between these circuit elements breaking ground loops, stopping internal switching noise from the DSP from entering the receiver circuitry, and preventing common mode signals from interfering with the desired RFID tag signal.

Claims

1. In a radio frequency identification (RFID) system having a detection zone for detecting the presence of an article in the detection zone wherein the article is tagged with a resonant intelligent tag,

(a) a receiver circuit which outputs a demodulated analog tag response signal upon detection of the intelligent tag in the detection zone;

(b) a tag response signal analyzing circuit including

(i) an input, and

(ii) a digital signal processing circuit which processes the analog tag response signal and outputs therefrom intelligent tag data; and

(c) an optical interface connected at one end to the output of the receiver circuit and connected at the other end to the input of the tag response signal analyzing circuit for communicating the analog tag response signal from the receiver circuit to the tag response signal analyzing circuit.

2. In an RFID system according to claim 1, the optical interface including:

(i) an optical transmitter,

(ii) an optical receiver, and

(iii) an optical fiber connected at one end to the output of the optical transmitter and at the other end to the input of the optical receiver.

3. In an RFID system according to claim 1, wherein the resonant intelligent tag is a radio frequency identification (RFID) tag.

4. In an RFID system according to claim 1, wherein the tag response signal is amplitude-modulated.