RFID reader front end

• US 7,773,945 B2
• Filed: 06/27/2005
• Issued: 08/10/2010
• Est. Priority Date: 06/27/2005
• Status: Active Grant

• Current Assignee: Novanta Corporation (Novanta Inc.)
• Original Assignee: ThingMagic, Inc. (Novanta Inc.)
• Inventors: Reynolds, Matthew Stephen
• Primary Examiner(s): Urban; Edward
• Assistant Examiner(s): Hannon; Christian A
• Application Number:
  US11/167,401
• Publication Number:
  US 20060293018A1
• Time in Patent Office: 1,870 Days
• Field of Search: 455/231, 455/324, 455/41.2, 455/41.3, 455/230, 455/280, 455/161.1, 455/161.2, 375/328, 375/349
• US Class Current: 455/41.3
• 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

An RFID reader analog front end architecture employs multiplexed use of a single analog to digital converter in order to digitize the inphase and quadrature components of the incoming signal from the reader'"'"'s receiving antenna. The Type 1 architecture includes an analog I/Q switch that controls which of the baseband signals will be digitized by a single Analog to Digital Converter. In the Type 2 architecture, the I/Q switch is moved so that it is directly adjacent to the receive mixers, requiring only one antialiasing filter block and gain block. In the Type 3 architecture, one mixer and its associated filtering chain are eliminated. The Type 4 architecture provides for selection of transmitter phase basis by means of an I/Q switch operating under control of the DSP that phase-shifts the transmitter with respect to the receiver.

Claims

1. A digital receiver circuit for a radio-frequency identification (RFID) tag reader comprising:

an analog receiver circuit receiving an RFID tag response to a transmitted command, the analog receiver circuit producing an inphase RFID tag response signal and a quadrature RFID tag response signal from the RFID tag response and having a first analog switch for selecting one of the inphase and quadrature signals for digitizing, wherein the first analog switch receives the inphase and quadrature signals from a quadrature hybrid and provides the inphase and quadrature signals to a single receiver mixer;

a single analog-to-digital converter connected via the first analog switch to the analog receiver circuit for digitizing the selected one of the inphase RFID tag response signal and the quadrature RFID tag response signal received from the analog receiver circuit;

a digital signal processor for decoding digitized RFID tag response signals from the analog-to-digital converter, determining whether the digitized RFID tag response signals decode correctly and if the digitized RFID tag signals do not decode correctly with the analog switch in a first switch state, switching the analog switch from the first switch state to a second switch state; and

a second analog switch for receiving the inphase and quadrature signals from the quadrature hybrid and controlling the provision of the signals via a transmitter to the receiver mixer.

2. The circuit of claim 1, wherein the first analog switch receives the inphase and quadrature signals from two receiver mixers.

3. The circuit of claim 2, wherein the signals received by the first analog switch are filtered and amplified before entering the first analog switch.

4. The circuit of claim 2, the analog receiver circuit further comprising a filter and an amplifier for filtering and amplifying the output of the first analog switch before the output is sent to the analog-to-digital converter.

5. A RFID reader front end system comprising:

a transmitter for transmitting a command to an RFID tag;

an analog receiver circuit receiving an RFID tag response to the transmitted command, the analog receiver circuit producing an inphase RFID tag response signal and a quadrature RFID tag response signal from the RFID tag response to the transmitted command and having a first analog switch for selecting one of the inphase and quadrature signals for digitizing, wherein the first analog switch receives the inphase and quadrature signals from a quadrature hybrid and provides them to a single receiver mixer;

a single analog-to-digital converter connected via the first analog switch to the analog receiver circuit for digitizing the selected one of the inphase RFID tag response signal and the quadrature RFID tag response signal received from the analog receiver circuit; and

a digital signal processor for decoding digitized RFID tag response signals from the analog-to-digital converter, determining whether the digitized RFID tag response signals decode correctly and if the digitized RFID tag signals do not decode correctly with the analog switch in a first switch state, switching the analog switch from the first switch state to a second switch state; and

a second analog switch for receiving the inphase and quadrature signals from the quadrature hybrid and providing them via a transmitter to the receiver mixer, the second analog switch being under the control of the digital signal processor.

6. The system of claim 5, wherein the first analog switch receives the inphase and quadrature signals from two receiver mixers.

7. The circuit of claim 6, wherein the signals received by the first analog switch are filtered and amplified before entering the first analog switch.

8. The system of claim 6, the analog receiver circuit further comprising a filter and an amplifier for filtering and amplifying the output of the first analog switch.

9. A method for converting received RFID tag response signals to digital signals, comprising the steps of:

receiving, by an analog receiver circuit, an RFID tag response signal from an RFID tag;

producing an inphase RFID tag response signal and a quadrature RFID tag response signal from the received RFID tag response signal;

selecting, by an analog switch, one of the inphase RFID tag response signal and the quadrature RFID tag response signal for digitizing;

digitizing, by an analog-to-digital converter, the selected one of the inphase RFID tag response signal and the quadrature RFID tag response signal;

decoding the digitized RFID tag response signal;

determining whether the digitized RFID tag response signal decoded correctly; and

if the digitized RFID tag signals do not decode correctly with the analog switch in a first switch state, switching the analog switch from the first switch state to a second switch state;

transmitting a command to the RFID tag;

receiving, by an analog receiver circuit, an RFID tag response to the transmitted command;

producing an inphase RFID tag response signal and a quadrature RFID tag response signal from the received RFID tag response to the transmitted command;

digitizing, by the analog-to-digital converter, one of the inphase RFID tag response signal and the quadrature RFID tag response signal selected with the analog switch in the second switch state;

decoding the digitized RFID tag response signal;

determining whether the digitized RFID tag response signal decodes correctly;

if the digitized RFID tag signal decodes correctly, sending the decoded data for further processing; and

if the digitized RFID tag signal does not decode correctly, reporting a decode failure.

10. The method of claim 9, wherein the inphase and quadrature signals are provided to the first analog switch via two receiver mixers.

11. The method of claim 10, further comprising the step of filtering and amplifying the signals received by the first analog switch before they enter the first analog switch.

12. The method of claim 10, further comprising the step of filtering and amplifying the output of the first analog switch before it is sent to the analog-to-digital converter.

13. The method of claim 9, wherein the inphase and quadrature signals are provided to the first analog switch from a quadrature hybrid and further including the step of providing the selected signal from the first analog switch to a single receiver mixer before it is sent to the analog-to-digital converter.

14. The method of claim 13, further comprising the steps of:

providing a second analog switch for receiving the inphase and quadrature signals from the quadrature hybrid; and

providing a selected one of the inphase and quadrature signals via a transmitter to the receiver mixer.