IIR Digital Pre-Distortion for GaN Amplifier Memory Effects
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Solution Overview
Problem
Power amplifiers in communication systems exhibit non-linearity, leading to spectral growth and distortions that interfere with adjacent channels and increase bit error rates, particularly in gallium nitride (GaN) based amplifiers due to long-term memory effects and changing RC time constants.
Innovation Solution
Implementing digital pre-distortion (DPD) systems with infinite impulse response (IIR) filters that selectively adjust parameters based on the amplifier's time constants, using models like gate-lag and drain-lag models to compensate for non-linearities and memory effects, thereby pre-distorting signals to extend the amplifier's linear response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power amplifiers are used to provide desired gain to transmitted signals, then signal amplification is achieved, but non-linearity causes spectral growth and distortions that interfere with adjacent channels
Solution Approach 1:
The patent applies digital pre-distortion (DPD) to modify the input signal before amplification. The DPD circuit pre-compensates for the amplifier's non-linear characteristics by applying inverse distortion, so that when the amplifier processes the pre-distorted signal, the output is linearized. This preliminary action prevents spectral growth and adjacent channel interference before they occur.
Solution Approach 2:
The patent dynamically adjusts DPD parameters including time constants and polynomial coefficients based on the amplifier's operating conditions. By changing these parameters in response to varying input signal levels and amplifier states, the system maintains optimal linearization performance across different operating points, effectively reducing spectral growth and distortions.
2Stability of the object's composition
If digital pre-distortion is implemented to compensate for amplifier non-linearities, then linearity of output response is improved, but device complexity increases due to additional processing circuits
Solution Approach 1:
The patent divides the DPD function into separate modular components: an IIR filter stage for memory effect compensation, a polynomial distortion compensation stage, and parameter selection logic. This segmentation allows each function to be implemented independently with optimized complexity, reducing overall circuit complexity while maintaining linearity improvement.
Solution Approach 2:
The patent uses lookup tables and pre-computed coefficient sets to represent complex amplifier characteristics. Instead of implementing full real-time modeling of amplifier non-linearities, the system uses copied parameter sets that approximate the amplifier behavior, significantly reducing computational complexity while preserving linearity compensation effectiveness.
3Measurement precision
If IIR filters with selectively implemented parameters are used to compensate for changing time constants, then compensation accuracy is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements dynamic parameter selection where the IIR filter time constants are switched based on the amplifier's instantaneous operating state. Rather than using fixed precision parameters, the system dynamically adapts parameters to match current amplifier conditions, reducing the need for extremely precise fixed parameter implementation while maintaining high compensation accuracy.
Solution Approach 2:
The patent uses discrete parameter sets that are selected based on amplifier operating conditions rather than continuously variable parameters. This approach reduces manufacturing precision requirements by using a limited set of well-defined parameter values that are easier to implement with standard digital components, while still achieving accurate compensation through parameter switching.
Data Source
AI summary
Described examples provide for digital communication circuits and systems that implement digital pre-distortion (DPD). In an example, a system includes a DPD circuit configured to compensate an input signal for distortions resulting from an amplifier. The DPD circuit includes an infinite impulse response (IIR) filter configured to implement a transfer function. The IIR filter includes a selection circuit configured to selectively output a selected parameter. The transfer function is based on the selected parameter.