System and method for sensitivity optimization of RF receiver using adaptive nulling
First Claim
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1. An RFID interrogating device connected to an antenna, comprising:
- an RF transmitter configured to form a transmit signal;
a first directional coupler configured to extract a first portion of the transmit signal;
a vector modulator configured to adjust the first portion of the transmit signal in phase and amplitude to form a nulling signal;
a second directional coupler configured to combine at least a portion of the nulling signal with a second portion of the transmit signal reflected from the antenna and at least a portion of a responding signal from an RFID tag received by the antenna,wherein the phase and amplitude of the first portion of the transmit signal is adjusted such that the nulling signal can be used to substantially cancel the second portion of the transmit signal reflected from the antenna;
a detector configured to detect a feedback portion of a combined signal from an output of the second directional coupler; and
a controller configured to receive an input signal formed from the feedback portion of the combined signal and to form at least one output signal based on the input signal,wherein the at least one output signal is used by the vector modulator to adaptively attenuate the first portion of the transmit signal and to adaptively change the phase of the first portion of the transmit signal.
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Abstract
The present invention provides sensitivity enhancement for a single antenna RFID interrogating device by separately coupling a nulling signal formed using a portion of a transmit signal into a receiver. The phase and amplitude of nulling signal can be adjusted so that the nulling signal cancels that a reflected transmit signal from the antenna, resulting in the small backscattered signal from the distant RFID tag to be more easily detected, and improving the sensitivity of the RFID receiver.
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12 Claims
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1. An RFID interrogating device connected to an antenna, comprising:
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an RF transmitter configured to form a transmit signal; a first directional coupler configured to extract a first portion of the transmit signal; a vector modulator configured to adjust the first portion of the transmit signal in phase and amplitude to form a nulling signal; a second directional coupler configured to combine at least a portion of the nulling signal with a second portion of the transmit signal reflected from the antenna and at least a portion of a responding signal from an RFID tag received by the antenna, wherein the phase and amplitude of the first portion of the transmit signal is adjusted such that the nulling signal can be used to substantially cancel the second portion of the transmit signal reflected from the antenna; a detector configured to detect a feedback portion of a combined signal from an output of the second directional coupler; and a controller configured to receive an input signal formed from the feedback portion of the combined signal and to form at least one output signal based on the input signal, wherein the at least one output signal is used by the vector modulator to adaptively attenuate the first portion of the transmit signal and to adaptively change the phase of the first portion of the transmit signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of interrogating a passive RFID tag performed by an RFID reader connected to an antenna, comprising:
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forming a transmit signal; extracting a first portion of the transmit signal; adjusting the first portion of the transmit signal in phase and amplitude to form a nulling signal; and combining at least a portion of the nulling signal with a second portion of the transmit signal reflected from the antenna, wherein the adjusting step comprises; splitting the first portion of the transmit signal into a first branch signal and a second branch signal; forming a first output signal from the first branch signal, a magnitude and polarity of the first output signal being dependent on a first voltage; forming a second output signal from the second branch signal, a magnitude and polarity of the second output signal being dependent on a second voltage; and combining the first and second output signals in quadrature. - View Dependent Claims (10, 11, 12)
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Specification