RFID transceiver device

• US 7,492,812 B2
• Filed: 08/24/2005
• Issued: 02/17/2009
• Est. Priority Date: 04/08/2005
• Status: Active Grant

• Current Assignee: Fujitsu Frontech Limited (Fujitsu Limited)
• Original Assignee: Fujitsu Limited
• Inventors: Kuroda, Osamu, Kawasaki, Yusuke, Tanaka, Yoshinori, Ninomiya, Teruhisa
• Primary Examiner(s): Bocure; Tesfaldet
• Application Number:
  US11/209,627
• Publication Number:
  US 20060229032A1
• Time in Patent Office: 1,273 Days
• Field of Search: 375/219, 375/222
• US Class Current: 375/219
• 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: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

An RFID transceiver device is capable of high sensitivity reception, by the reduction of noise, irrespective of the distance to the tag. The RFID transceiver device includes a delay circuit between a local oscillation circuit and a demodulation circuit, wherein the amount of delay of the delay circuit is set to a magnitude corresponding to the path difference between the path of leakage, via a duplexer into the demodulation circuit, of transmission signal output from the local oscillation circuit for transmission, and the path of direct input of the local oscillation signal from the local oscillation circuit to the demodulation circuit.

Claims

1. An RFID transceiver device comprising:

a local oscillation circuit that generates a local oscillation signal;

a demodulation circuit that demodulates a reception signal using the frequency of the local oscillation signal output from said local oscillation circuit;

a transmission circuit that modulates, amplifies and transmits a local oscillation signal output from said local oscillation circuit;

a duplexer that supplies to a transceiving antenna the transmission signal from said transmission circuit and branches the reception signal received by said transceiving antenna to said demodulation circuit; and

a delay circuit between said local oscillation circuit and said demodulation circuit, wherein

the amount of delay of said delay circuit is set to a magnitude corresponding to the path difference between the path of the leakage, via said duplexer into said demodulation circuit, of the transmission signal that is output from said local oscillation circuit for transmission, and the path of direct input of the local oscillation signal from said local oscillation circuit to said demodulation circuit.

2. The RFID transceiver device according to claim 1, further comprising a control and processing circuit that detects noise level in accordance with the output of said demodulation circuit, wherein said control and processing circuit controls the delay amount of said delay circuit on the basis of said detected noise level.

4. The RFID transceiver device according to any of claim 1 further comprising:

a transceiving antenna; and

a delay circuit that connects said transceiving antenna to said duplexer, wherein the amount of delay of the delay circuit is set such that the impedance of said transceiving antenna seen from said duplexer is substantially equal to the characteristic impedance.

5. The RFID transceiver device according to claim 2, wherein

detection of the noise level in said performed in a condition in which command transmission from said transmission circuit to the tag is halted.

3. An RFID transceiver device comprising:

a local oscillation circuit that generates a local oscillation signal;

a demodulation circuit that demodulates a reception signal using the frequency of the local oscillation signal output from said local oscillation circuit;

a modulation circuit that modulates the local oscillation signal output from said local oscillation circuit;

a duplexer that supplies to a transceiving antenna the transmission signal output from said modulation circuit and branches the reception signal received by said transceiving antenna to said demodulation circuit; and

a path for supplying the transmission signal output from said modulation circuit as the local oscillation signal to said demodulation circuit, wherein the amount of delay on said path and the amount of delay on the path of the leakage of the transmitted carrier signal that is input to said demodulation circuit through said duplexer are set to the same magnitude.