Quarter wave phase shifted diode detector circuit

A phase shifting diode detector system for an RFID reader comprising:

• quarter-wave delay circuitry 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;
• and
• 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, at a first end of each diode pair, to produce opposite rectified signal output polarities, and wherein the second end of each diode pair is coupled to ground;
• wherein the input to a first one of the bridges is capacitively coupled to the first end of the delay circuitry, and the input to the second one of the bridges is capacitively coupled to the second end of the delay circuitry, wherein the input to each of the bridges is connected to the junction between each said diode pair.

A phase shifting diode detector system for an RFID reader comprising:

• quarter-wave delay circuitry coupled between a forward transmitted sine wave signal of the RFID reader applied at a first end of the delay circuitry, and a reflected sine wave signal returning from an RFID tag applied at a second end of the delay circuitry;
• and
• 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;
• wherein the bridges each have an input, connected to the junction between each said diode pair, capacitively coupled to a respective opposite end of the delay circuitry;
• wherein the transmitted sine wave enters the quarter-wave delay circuitry at one end and the received sine wave enters from the opposite end, causing both wave fronts to produce voltages that are phase-shifted 90 degrees to create two DC voltages are of the same polarity which are added in a summing amplifier to double the signal amplitude;
• and
• wherein each of the diode detector bridges rectifies the transmitter's carrier amplitude signal to generate rectified output voltages that are in proportion to, and opposite in polarity from, the envelope of the transmitter carrier, wherein the output voltages are fed in series to cancel the amplitude noise component of the signal returning from the RFID tag.

A diode detector system for an RFID reader comprising:

• 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 modulated signals having opposite rectified signal polarities;
• wherein a forward transmitted signal of the RFID reader and a reflected signal returning from an RFID tag are separated by a phase shift of 90 degrees, and are applied to both inputs of the pair of diode detector bridges;
• and
• wherein the junction between each said diode pair corresponds to the input in each of the bridges.