Predistortion system and method using analog feedback loop for look-up table training

A method for generating a predistorted drive signal for a nonlinear transmission path that includes a power amplifier, comprising the steps of:

• A) utilizing an analog feedback system to determine a complex error signal that linearizes the nonlinear transmission path;
• and
• B) determining a magnitude of a complex input signal and generating a predistorted drive signal for the nonlinear transmission path that includes the power amplifier,
• wherein determining a magnitude of the complex input signal and generating a predistorted drive signal for the nonlinear transmission path includes:
• C) converting the complex error signal to baseband digital format;
• D) determining a complex gain coefficient corresponding to a preselected power level and storing the complex gain coefficient in a look-up table;
• E) determining a magnitude of the complex input signal and generating an index based on the magnitude of the complex input signal and the preselected power level;
• F) using the look-up table to output the complex gain coefficient corresponding to the index;
• and
• G) multiplying the complex input signal and the complex gain coefficient to provide the predistorted drive signal.

A radio having a linearization system for providing a predistorted drive signal for a nonlinear transmission path that includes a power amplifier, the linearization system comprising:

• A) an analog feedback system that includes the nonlinear transmission path, coupled to the computation unit, for determining the complex error signal that linearizes the nonlinear transmission path;
• and
• B) a computation unit, coupled to the analog feedback system and coupled to receive a complex input signal and a complex error signal, for determining a magnitude of the complex input signal and generating the predistorted drive signal for the nonlinear transmission path that includes the power amplifier,
• wherein the computation unit includes:
• C) a ratio determiner, coupled to the interface circuitry and to receive the complex input signal, for determining a complex look-up table coefficient corresponding to a preselected signal level;
• D) a lookup encoder, coupled to receive the complex input signal, for determining a magnitude of the complex input signal and generating an index based on the magnitude of the complex input signal and a preselected set of levels;
• E) a look-up table, coupled to the ratio determiner and the lookup encoder, for outputting the complex look-up table coefficient corresponding to the index;
• and
• F) a multiplier, coupled to receive the complex input signal and the complex look-up table coefficient, for multiplying the complex input signal and the complex look-up table coefficient to provide the predistorted drive signal.