Transmitter and method with rf power amplifier having predistorted bias

A method of operating a bias-stabilized RF transmitter comprising:

• generating an envelope tracking signal which tracks an envelope of an RF communication signal;
• producing a derivative with respect to time of said envelope tracking signal;
• delaying said envelope tracking signal to produce a delayed function of said envelope tracking signal;
• performing a mathematical operation upon said derivative with respect to time of said envelope tracking signal to produce a bias stabilization signal;
• applying a predistorted bias signal formed from said delayed function of said envelope tracking signal and said bias stabilization signal to an input of an envelope amplifier;
• and
• passing an amplified predistorted bias signal from an output of said envelope amplifier through an RF choke to a conduction channel node of an RF power amplifier configured to linearly amplify said RF communication signal by operating in a saturation region for said RF power amplifier, wherein said amplified predistorted bias signal at said conduction channel node of said RF power amplifier becomes altered to more closely resemble said envelope tracking signal by a distortion which results from passing said amplified predistorted bias signal through said RF choke.

A bias-stabilized RF transmitter comprising:

• an RF choke having first and second nodes;
• an envelope amplifier having an output coupled to said first node of said RF choke and having an input;
• an RF power amplifier having a conduction channel node coupled to said second node of said RF choke and configured to linearly amplify an RF communication signal by operating in a saturation region for said RF power amplifier;
• a target bias signal generator configured to generate a target bias signal that will be transformed into a stabilized bias signal at said conduction channel node of said RF power amplifier, said target bias signal being configured to maximize power-added efficiency of said RF power amplifier while maintaining insensitivity of an amplified RF communication signal produced by said RF power amplifier to variance in said stabilized bias signal;
• a bias distortion estimator configured to estimate an amount by which said stabilized bias signal will fail to match said target bias signal and to form a bias stabilization signal which compensates for said amount;
• and
• a merging section having inputs coupled to said target signal generator and to said bias distortion estimator and having an output coupled to said input of said envelope amplifier, said merging being configured to form a predistorted bias signal from said target bias signal and said bias stabilization signal;
• wherein said predistorted bias signal is applied to said input of said envelope amplifier, said envelope amplifier generates an amplified predistorted bias signal, said amplified predistorted bias signal passes through said RF choke to said conduction channel node of said RF power amplifier to become transformed by distortion into said stabilized bias signal, and said stabilized actual bias signal more closely resembles said target bias signal than said predistorted bias signal resembles said target bias signal.