Adaptive DPD Circuit Mitigates Power Amplifier Thermal Non-Linearity

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Solution Overview

Problem

Power amplifiers in communication systems exhibit limited linearity, leading to performance degradation due to non-linearities caused by thermal changes and trapping effects, which result in spectral growth and increased bit error rates.

Innovation Solution

Implementing digital pre-distortion (DPD) circuits with infinite impulse response (IIR) filters that adaptively adjust parameters in the transfer function to compensate for thermal changes, thereby mitigating non-linearities and extending the linear response of power amplifiers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If power amplifiers are used to provide gain in communication systems, then signal amplification is achieved, but linearity is limited due to thermal changes and trapping effects

Engineering Contradiction:

Improvesignal amplificationVSAvoidlinearity

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The DPD circuit pre-distorts the input signal before it reaches the power amplifier by applying the inverse of the anticipated non-linear distortion. This preliminary action compensates for thermal changes and trapping effects, ensuring that the amplifier's output remains linear despite its inherent non-linear characteristics varying with temperature and time constants

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses feedback from the amplifier's output to continuously monitor and adjust the DPD parameters. By comparing the actual output with the expected linear output, the system adapts the pre-distortion parameters in real-time to maintain linearity as thermal conditions and amplifier characteristics change during operation

Inventive Principle:

Principle #23Feedback

2Reliability

If adaptive parameters are implemented in IIR filters to compensate for thermal changes, then linearity is improved, but device complexity increases

Engineering Contradiction:

ImprovelinearityVSAvoidDPD circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system changes the parameters of the IIR filter in the DPD circuit adaptively based on detected thermal changes and amplifier performance. By dynamically adjusting filter coefficients and time constants, the system maintains linearity compensation effectiveness across varying operating conditions without requiring a completely different circuit architecture

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The DPD circuit transitions from static parameters to dynamic, adaptive parameters that automatically adjust to thermal and operational changes. This dynamic approach allows the system to maintain high linearity performance across varying conditions while using a single adaptable circuit rather than multiple fixed circuits for different conditions

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS11251819B1Thermal effect mitigation for digital pre-distortion

Publication Date: 2022.02.15 XILINX INC

AI summary

A transmitter for a communication system comprises a digital pre-distortion (DPD) circuit configured to generate a digital intermediate signal by compensating an input signal for distortions resulting from an amplifier, and an adaptation circuitry configured to update the first parameter based on the adjustment signal, the input signal, and an output signal output by the amplifier and based on the digital intermediate signal. The DPD circuit includes an infinite impulse response filter configured to implement a transfer function based on a first parameter, and thermal tracking circuitry configured to generate an adjustment signal corresponding to a thermal change of the amplifier.