Abstract: A system for increasing the sensitivity of a receiver in an RFID tag reader. The system includes a directional coupler which receives the signal transmitted by the reader and which receives a backscatter signal from the RFID tag. The output of the directional coupler includes a transmit reference signal and a combined signal comprising the received signal and a transmit leakage signal. A first feedback loop generates an amplitude-compensated reference signal including a transmit signal component having the same amplitude as the transmit leakage signal. A second feedback loop adjusts the phase angle of the amplitude-compensated reference signal to a phase angle 180 degrees out-of-phase with the combined signal, to generate a canceling signal which effectively cancels out the transmit leakage signal component of the combined signal thereby improving the signal-to-noise ratio thereof.

Abstract: A phase shifting diode detector system for an RFID reader. Quarter-wave delay circuitry is coupled between a forward transmitted signal of the RFID reader applied at a first end of the delay circuitry, and a reflected signal returning from an RFID tag applied at a second end of the delay circuitry. The system includes a pair of diode detector bridges, each comprising a series-coupled diode pair configured such that diode polarities in each bridge are reversed relative to the output thereof, to produce opposite rectified signal output polarities. An input to each of the bridges is capacitively coupled, from the junction between each said diode pair, to a respective opposite end of the delay circuitry.

Abstract: A phase shifting diode detector system for an RFID reader. Quarter-wave delay circuitry is coupled between a forward transmitted signal of the RFID reader applied at a first end of the delay circuitry, and a reflected signal returning from an RFID tag applied at a second end of the delay circuitry. The system includes a pair of diode detector bridges, each comprising a series-coupled diode pair configured such that diode polarities in each bridge are reversed relative to the output thereof, to produce opposite rectified signal output polarities. An input to each of the bridges is capacitively coupled, from the junction between each said diode pair, to a respective opposite end of the delay circuitry.