RFID reader and method for removing a transmission carrier leakage signal

Abstract

A radio frequency identification (RFID) reader is provided, having a transmitting circuit that generates a transmitted signal to operate an RFID tag, a receiving circuit that receives a received signal including a tag signal from the RFID tag and a transmission carrier leakage signal leaking from the transmitting circuit, and a leakage removing circuit that senses a phase and amplitude of the transmission carrier leakage signal inputted to the receiving circuit, converts the transmitted signal from the transmitting circuit into a signal having a phase opposite to that of the transmission carrier leakage signal and an amplitude equal to that of the transmission carrier leakage signal, and synthesizes the converted signal and the received signal inputted to the receiving circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will be more apparent by describing certain exemplary embodiments of the present invention with reference to the accompanying drawings, in which:

FIG. 1 is a schematic circuit diagram of a related RFID system composed of an RFID tag and an RFID reader 10;

FIG. 2 are graphs illustrating a transmission carrier leakage signal, an RFID tag signal, and a received signal generated in the RFID system of FIG. 1;

FIGS. 3A and 3B are circuit diagrams of a canceller circuit in a related RFID system and an RFID reader adopting the canceller;

FIG. 4 is a circuit diagram of an RFID reader having a leakage removing circuit according to an exemplary embodiment of the present invention; and

FIG. 5 is a detailed circuit diagram of a circuit part through which the leakage removing circuit of FIG. 4 and a receiving circuit are connected to each other.

FIG. 6 is a flowchart diagram showing the process for removing a transmission carrier leakage signal in an RFID system according to an exemplary embodiment of the present invention.

Claims

1. A radio frequency identification (RFID) reader comprising: a transmitting circuit which generates a transmitted signal to operate an RFID tag;a receiving circuit which receives a received signal including a tag signal from the RFID tag and a transmission carrier leakage signal leaking from the transmitting circuit; anda leakage removing circuit which senses a phase and an amplitude of the transmission carrier leakage signal inputted to the receiving circuit, converts the transmitted signal from the transmitting circuit into a signal having a phase opposite to that of the transmission carrier leakage signal and an amplitude equal to that of the transmission carrier leakage signal, and synthesizes the converted signal and the received signal inputted to the receiving circuit.

2. The RFID reader of claim 1, wherein the leakage removing circuit comprises: a gain amplifier which converts the amplitude of the transmitted signal from the transmitting circuit; anda phase shifter which generates an offset signal by adjusting the phase of the transmitted signal from the gain amplifier so that the phase of the transmitted signal becomes opposite to the phase of the transmission carrier leakage signal.

3. The RFID reader of claim 2, further comprising a signal detector installed on the receiving circuit which detects the transmission carrier leakage signal inputted to the receiving circuit and the offset signal generated through the gain amplifier and the phase shifter.

4. The RFID reader of claim 3, wherein the leakage removing circuit further comprises: a first switch mounted on a front end of the signal detector on the receiving circuit which switches the input of the received signal on/off; anda second switch arranged on a signal line which connects the transmitting circuit and the receiving circuit with each other to switch on/off the offset signal to the receiving circuit.

5. The RFID reader of claim 4, wherein when the signal detector detects the transmission carrier leakage signal, the first switch is turned on, and the second switch is turned off.

6. The RFID reader of claim 5, wherein when the signal detector detects the offset signal, the first switch is turned off, and the second switch is turned on.

7. The RFID reader of claim 6, wherein when the RFID tag is detected, both the first switch and the second switch are turned on, and the received signal inputted to the receiving circuit and the offset signal from the leakage removing circuit are synthesized to remove the transmission carrier leakage signal in the receiving circuit.

8. A radio frequency identification (RFID) reader having a transmitting circuit generating a transmitted signal to operate an RFID tag and a receiving circuit receiving a received signal including a tag signal from the RFID tag and a transmission carrier leakage signal leaking from the transmitting circuit, the RFID reader comprising: a gain amplifier converting the amplitude of the transmitted signal from the transmitting circuit;a phase shifter generating an offset signal by adjusting the phase of the transmitted signal from the gain amplifier so that the phase of the transmitted signal becomes opposite to the phase of the transmission carrier leakage signal; anda signal detector installed on the receiving circuit to detect the transmission carrier leakage signal inputted to the receiving circuit and the offset signal generated through the gain amplifier and the phase shifter.

9. A method for removing a transmission carrier leakage signal in a radio frequency identification (RFID) reader, the method comprising: measuring the amplitude and phase of a transmission carrier leakage signal;creating an offset signal by adjusting the transmitted signal such that the offset signal has an amplitude equal to the transmission carrier leakage signal and a phase opposite to the transmission carrier leakage signal; andsynthesizing the offset signal and a signal received from an RFID tag to remove the transmission carrier leakage signal from the received signal.