Compensation for holes in the read range of an RFID reader technical field

• US 7,844,238 B2
• Filed: 12/05/2005
• Issued: 11/30/2010
• Est. Priority Date: 12/05/2005
• Status: Expired due to Fees

• Current Assignee: Assa Abloy AB
• Original Assignee: Assa Abloy AB
• Inventors: Sherrets, David L.
• Primary Examiner(s): Tran; Pablo N
• Application Number:
  US11/294,635
• Publication Number:
  US 20070129039A1
• Time in Patent Office: 1,821 Days
• Field of Search: 455/230, 455/41.1, 455/41.2, 455106-107, 455/231, 455/240.1, 455/245.1, 455/247.1, 455/334, 455/70, 455/73, 455/550.1, 340/10.1, 340/10.52, 340/572.1, 340/572.8, 340/573.4, 340/572.7, 340/572.5, 235/376, 235/487, 342/42, 342/44
• US Class Current: 455/230
• 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

Abstract

A reader and a corresponding method are provided for processing transponder data signals received from a transponder in an RFID system. The reader includes an exciter which generates excitation signals, a receiver which conditions the transponder data signals, an antenna coupled to the exciter and receiver which transmits the excitation signals and receives the transponder data signals, and a controller coupled to the receiver. The controller receives the conditioned transponder data signals and demodulates the conditioned signals to extract the transponder data. The controller is configured to detect the amplitude of the conditioned signals and to control operation of the receiver as a function of the amplitude of the conditioned signals.

Claims

1. A reader for an RFID system comprising:

an antenna configured to receive a transponder data signal;

a receiver coupled to said antenna for generating a conditioned output signal from said transponder data signal; and

a controller coupled to said receiver for detecting amplitude of said conditioned output signal, determining a tag state based on said amplitude, and controlling operation of said receiver as a function of said tag state, wherein said antenna signal has a voltage value exceeding an upper voltage tolerance level of an amplifier and a high voltage reduction circuit conveys peak portions of said antenna signal to said amplifier for reducing said voltage value below said upper voltage tolerance level of said amplifier.

2. The reader of claim 1, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces said amplitude of said conditioned output signal by adjusting voltage reduction performed by said high voltage reduction circuit.

3. The reader of claim 1, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces said amplitude of said conditioned output signal by adjusting a the gain of said amplifier.

4. The reader of claim 1, wherein said controller includes an input circuit coupled to said amplifier, wherein said input circuit detects said amplitude of said conditioned output signal.

5. A reader for an RFID system comprising:

an antenna to receive a transponder data signal;

a receiver coupled to said antenna, said receiver including a voltage reduction circuit for receiving an antenna signal including said transponder data signal from said antenna and generating a voltage reduced signal, said receiver further including an amplifier coupled to said voltage reduction circuit for receiving said voltage reduced signal and generating a conditioned amplifier output signal; and

a controller coupled to said amplifier for demodulating said conditioned amplifier output signal, thereby reading said transponder data signal, wherein said controller detects an-amplitude of said conditioned amplifier output signal, determines a tag state based on said amplitude, and adjusts at least one of (i) a gain of said amplifier and (ii) amplitude of said voltage reduced signal as a function of said tag state.

6. The reader of claim 5, wherein said voltage reduction circuit is a shift and clamp circuit for isolating a portion of said antenna signal.

7. The reader of claim 6, wherein said controller controls amplitude of a shift current applied to said shift and clamp circuit.

8. The reader of claim 5 further comprising an automatic gain control circuit coupled to said amplifier for adjusting said gain of said amplifier as a function of said amplitude.

9. The reader of claim 5 further comprising an automatic gain control circuit coupled to said voltage reduction circuit for adjusting said amplitude of said voltage reduced signal as a function of said amplitude of said conditioned amplifier output signal.

10. The reader of claim 5, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces said gain of said amplifier.

11. The reader of claim 5, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces said amplitude of voltage reduced signal by adjusting an amount of voltage reduction performed by said voltage reduction circuit.