Direct conversion polar transmitter for an RFID reader

A method of operating a transmitter for a radio frequency identification (RFID) system, the method comprising:

• producing, using a processor, a cartesian in-phase signal and a cartesian quadrature-phase signal;
• supplying the cartesian in-phase signal and the cartesian quadrature-phase signal to a quadrature modulator;
• supplying a continuous wave signal to the quadrature modulator;
• supplying an envelope signal from an envelope amplifier to a power amplifier;
• and
• driving the power amplifier using the quadrature modulator to produce a transmitter output signal.

Apparatus for radio frequency identification (RFID) comprising:

• means for producing a cartesian in-phase signal and a cartesian quadrature-phase signal;
• means for supplying an envelope signal to a power amplifier;
• means for supplying a continuous wave signal for use in modulating the power amplifier;
• and
• means for modulating the power amplifier using the cartesian in-phase signal and the cartesian quadrature-phase signal to produce a transmitter output signal.

A radio frequency (RF) system comprising:

• a power amplifier to produce a transmitter output signal;
• an envelope amplifier connected to the power amplifier to supply an envelope signal to the power amplifier;
• a quadrature modulator connected to the power amplifier to provide modulation for the transmitter output signal using a cartesian input signal;
• and
• a continuous wave source connected to the quadrature modulator.