Amplifier modulation method and apparatus

A power amplifier, comprising:

• a signal generator configured to receive an input signal having an envelope and configured to provide:
• a drive signal that is modulated with a carrier wave during a first time and inactive during a second time, and a pulse-width modulation signal that is driven at a first state during the first time and driven at a second, different state during the second time;
• and
• a switched mode power amplification stage configured to, in conjunction with a filter coupled between a differential output of the power amplification stage, provide an amplified output voltage at the differential output as a function of the drive signal and an inverse drive signal;
• and
• impedance compensation circuitry coupled to the differential output of the power amplification stage and configured to selectively alter an output impedance of the power amplification stage as a function of the pulse-width modulation signal.

A method for modulating an input signal, comprising:

• generating an envelope signal based on an input signal having an envelope;
• generating a pulse-width modulation signal by comparing the envelope signal to a sampling signal, where the pulse-width modulation signal is driven at a first state during a first time and driven at a second, different state during a second time;
• generating a drive signal that exhibits a carrier wave frequency during the first time and is inactive during the second time;
• generating an amplified output signal at an output of a power amplification stage by using the drive signal;
• filtering the amplified output signal using a filter coupled to the output of the power amplification stage;
• and
• altering an output impedance of the power amplification stage as seen from the filter as a function of the pulse-width modulation signal.

A radio frequency transmitter, comprising:

• an envelope detector configured to receive the input signal and provide an envelope signal therefrom;
• a comparator configured to receive the envelope signal and provide a pulse-width modulation signal that is continuously do asserted driven at a first state during a first time and driven at a second, different state during a second time;
• conditioning circuitry configured to logically relate the pulse-width modulation signal with a carrier wave and thereby provide a drive signal;
• a power amplification stage configured to provide an amplified output voltage at a first singled ended output, comprising:
• a first MOSFET for providing the amplified output voltage as a function of the conditioned pulse-width modulation signal;
• a filter coupled to the first single-ended output branch and configured to provide a filtered output signal, the filtered output signal having a envelope that is similar to that of the input signal and having a frequency that is greater than that of the input signal;
• and
• first impedance compensation circuitry coupled to the first single-ended output and including a third switching element configured to selectively alter an output impedance of the power amplification stage as a function of the pulse-width modulation signal.

A power amplifier, comprising:

• signal generator means for receiving an analog input signal and for providing a drive signal that is modulated with a carrier wave during a first time and inactive during a second time, and a pulse-width modulation signal that is driven at a first state during the first time and driven at a second, different state during the second time;
• power amplification means for providing an amplified output voltage as a function of the drive signal;
• and
• impedance compensation means for selectively altering an output impedance of the power amplification means as a function of the pulse-width modulation signal.