Digital linearization circuit

A complex base-band adaptive digital pre-distorter circuit for providing signal distortion side band suppression and memory effect compensation for an input signal envelope response dependency of a nonlinear device, comprising:

• an inverse complex gain look-up table memory configured to be read using an amplitude or power of an input signal to provide an inverse complex gain correction;
• a complex multiplier for multiplying the input signal with an inverse complex to produce a gain correction feeding a distorted signal provided to a nonlinear device;
• a measurement receiver for sampling an output signal from the nonlinear device to provide a digital base-band output signal to be compared with the input signal;
• a time alignment circuitry configured to time align the input signal and the digital base-band output signal on a sample-by-sample basis;
• a phase alignment circuitry configured to phase align complex I/Q-signals in the digital signal processing by phase multiplication and alignment of the input complex digital base-band I/Q signal,
• wherein values adapted to an inverse complex gain look-up table memory are evaluated by calculating a complex gain of a combined digital pre-distorter and the nonlinear device, the nonlinear device including digital-to-analog converters (DAC) and up-converters,
• wherein a virtual complex gain table situated in a digital signal processor (DSP) memory is updated adaptively by using an adaptive virtual digital filter also in the DSP for correct weighting of the complex gain evaluations and wherein the inverse of the virtual complex gain table is loaded into the inverse complex gain look-up table in the digital pre-distorter circuit for each adaptation,
• wherein a performance measure of the digital pre-distorter circuit is evaluated either by comparing difference in impulse response values of the adaptive virtual digital filter in the DSP for each adaptation or a difference in complex gain values, and
• wherein the digital base-band output signal is an output of a digital base-band model modeling a behavior of the nonlinear device, the digital base-band model including a plurality of cascaded digital function blocks, each digital function block configured to model the distortion due to a specific distortion type, and each digital function block being independent of other digital function blocks.

A method to linearly transform a nonlinear device, comprising:

• formulating a digital base band model of the nonlinear device, wherein the digital base band model is a model of a behavior of the nonlinear device;
• and
• determining a predistortion circuit, using the digital base band model, having an inverse functionality of the digital base band model,
• wherein the act of formulating the digital base band model comprises:
• deriving a plurality of distortion function blocks related to the nonlinear device, wherein each distortion function block si configured to model an effect of a particular type of distortion independent of other distortion function blocks;
• and
• cascading the plurality of distortion function blocks.