Method and apparatus for linear amplification of a radio frequency signal

An apparatus for the linear amplification of a radio frequency signal, the apparatus comprising:

• an amplifier having at least one input port coupled to receive a modulated input signal and an output port that is effective to produce an output signal based on the modulated input signal;
• a first modulator, coupled to the at least one input port of the amplifier, that is effective to generate a modulated input signal responsive to at least one control signal;
• a signal coupler, coupled to the output port of the amplifier, that is effective to sample a portion of the output signal to produce an attenuated output signal;
• a polar feedback circuit, coupled to the signal coupler and at least the first modulator, that is effective to receive a baseband input signal, to determine a modulation error between the baseband input signal and the attenuated output signal, and to generate the at least one control signal to reduce the modulation error, wherein the polar feedback circuit comprises:
• a second modulator that is effective to produce a phase modulated reference signal corresponding to a phase variation of the baseband input signal;
• a phase-shifting circuit, coupled to the second modulator, that is effective to introduce an approximately ninety degree phase offset to the phase modulated reference signal to produce a phase-shifted reference signal;
• and
• a first mixer, coupled to the phase-shifting circuit, the signal coupler, and the first modulator, that is effective to produce at least one control signal representing a phase modulation error based on a difference between the attenuated output signal and the phase-shifted reference signal.

A method for amplifying a radio frequency signal comprising the steps of:

• receiving a composite baseband signal, wherein the phase modulated baseband signal comprises an amplitude component;
• amplifying the radio frequency signal;
• amplitude modulating the radio frequency signal based on the amplitude component of the composite baseband signal;
• modulating the amplified and amplitude modulated radio frequency signal to produce an output signal;
• sampling a portion of the output signal to produce an attenuated output signal;
• determining a desired attenuated output signal based on the composite baseband signal;
• comparing the desired attenuated output signal to the attenuated output signal;
• determining a modulation error based on a difference between the attenuated output signal and the desired attenuated output signal;
• producing at least one control signal based on the modulation error;
• and
• adjusting the amplified and amplitude modulated radio frequency signal based on the at least one control signal to produce a corrected output signal.

A method for amplifying a radio frequency signal comprising the steps of:

• receiving a composite baseband signal, wherein the composite baseband signal comprises a phase component and an amplitude component;
• phase modulating the radio frequency (RF) signal based on the phase component of the composite baseband signal to produce a phase modulated RF signal;
• amplifying the phase modulated RF signal;
• modulating the amplitude of the phase modulated RF signal based on the amplitude component of the composite baseband signal;
• modulating the amplified and amplitude modulated phase modulated RF signal to produce an output signal;
• sampling a portion of the output signal to produce an attenuated output signal;
• downconverting the attenuated output signal to produce a downconverted attenuated output signal;
• comparing the composite baseband signal and the downconverted attenuated output signal;
• determining a modulation error based on a difference between the downconverted attenuated output signal and the composite baseband signal;
• producing at least one control signal based on the modulation error;
• and
• adjusting the amplified and amplitude modulated phase modulated RF signal based on the at least one control signal to produce a corrected output signal.

A communication device comprising:

• a receiver;
• a linear transmitter comprising:
• an amplifier having at least one input port coupled to receive a modulated input signal and an output port that produces an amplified modulated signal;
• a complex modulator, coupled to the output port of the amplifier, that further modulates the amplified modulated signal responsive to at least one control signal to produce an output signal;
• a signal coupler, coupled to the complex modulator, that samples a portion of the output signal to produce an attenuated output signal;
• and
• a feedback circuit, coupled to the signal coupler and at least the complex modulator, that receives a quadrature modulation information signal from an information source, receives the attenuated output signal from the signal coupler, determines a modulation error based on quadrature modulation information signal and the attenuated output signal, and generates the at least one control signal to reduce the modulation error.