Method and apparatus for detecting and compensating for undesired phase shift in a radio transceiver

In a Cartesian, in-phase and quadrature (I/Q) radio frequency (RF) transmission system, a method comprising the steps of:

• modulating a carrier signal with a difference signal based on an input signal;
• transmitting the modulated carrier signal;
• detecting the transmitted signal and producing a detected signal;
• and
• demodulating the detected signal and generating a feedback signal;
• determining a difference between the input signal and the feedback signal to generate the difference signal;
• and
• compensating for phase error in the detected signal using the carrier signal, wherein the modulating step includes:
• modulating the carrier signal using a difference between an in-phase and quadrature components of the input and feedback signals, and
• wherein the compensating step includes:
• In-phase and quadrature (I/Q) demodulating the detected signal using the carrier signal as a reference signal and generating in-phase and quadrature (I/Q) demodulated outputs;
• In-phase and quadrature (I/Q) modulating the in-phase and quadrature (IQ) demodulated outputs using the carrier signal as a reference to generate a compensated carrier signal;
• and
• In-phase and quadrature (I/Q) demodulating the detected signal using the compensated carrier signal as a reference to generate in-phase and quadrature feedback component;
• limiting the amplitude of the carrier signal before the carrier signal is modulated using the difference between the in-phase and quadrature components of the input and the feedback signals, and
• limiting the amplitude of the compensated carrier signal.

A radio transmitter comprising:

• a local oscillator for generating a local oscillator signal;
• an I/Q modulator for modulating an input signal having in-phase (I) and quadrature (Q) components onto the local oscillator signal to generate a forward signal;
• a power amplifier receiving and amplifying the forward signal;
• an antenna for transmitting the amplified signal;
• a detector for detecting the transmitted signal;
• a phase adjuster, connected to the local oscillator and to the detector, for substantially continuously detecting and cancelling undesired phase shifts in the detected signal;
• a quadrature demodulator, connected to the phase adjuster for demodulating the detected signal in accordance with the local oscillator signal whose phase is adjusted by the phase adjuster to generate feedback in-phase and quadrature signals that are combined in first and second combiners with the input signal I and Q components, respectively;
• wherein the phase adjuster comprises:
• a second quadrature demodulator having the forward signal connected to one input port and the detected signal connected to a second input port and generating second in-phase and quadrature signals;
• first and second detectors for removing the amplitude fluctuations of the second in-phase and quadrature signals, respectively;
• and
• a second quadrature modulator connected to the local oscillator and receiving output signals from the first and second detectors and generating the phase adjusted local oscillator signal.