A
system for digitally linearizing the nonlinear behaviour of RF high efficiency amplifiers employing
baseband predistortion techniques is disclosed. The
system provides additive or multiplicative
predistortion of the digital quadrature (I / Q) input
signal in order to minimize
distortion at the output of the
amplifier. The predistorter uses a discrete-time
polynomial kernel to model the inverse transfer characteristic of the
amplifier, providing separate and simultaneous compensation for nonlinear static
distortion, linear dynamic
distortion and nonlinear dynamic effects including reactive electrical memory effects. Compensation for thermal memory effects also is embedded in the nonlinear dynamic compensation operation of the predistorter and is implemented parametrically using an autoregressive dynamics tracking mechanism. A
predistortion controller periodically monitors the output of the
amplifier and compares it to the quadrature input
signal to compute estimates of the residual output distortion of the amplifier. Output distortion estimates are used to adaptively compute the values of the parameters of the predistorter in response to changes in the amplifier's operating conditions (temperature drifts, changes in modulation input bandwidth, variations in drive level, aging, etc). The predistortion parameter values computed by the predistortion controller are stored in non-
volatile memory and used in the polynomial digital predistorter. The digital predistortion
system of the invention may provide
broadband linearization of highly nonlinear and highly efficient RF amplification circuits including, but not limited to, dynamic load modulation amplifiers.