Analog Predistortion Circuit for Power Amplifier Memory Distortion
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Solution Overview
Problem
Power amplifiers in transceivers face challenges with memory distortion at high frequencies, which is difficult to correct using digital predistortion due to increased complexity and cost, especially when dealing with phase and gain distortions.
Innovation Solution
An analog predistortion (APD) system is introduced to offset memory effects by applying predistortion to both phase and gain portions of the signal, combined with memoryless or low-depth memory digital predistortion (DPD), utilizing varactors with s-shaped capacitance to correct phase and gain distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If digital predistortion (DPD) is used to correct memory distortion in power amplifiers, then linearity improvement is achieved, but device complexity and cost increase significantly
Solution Approach 1:
The patent replaces complex digital signal processing systems with an analog predistortion circuit that uses continuous-time filtering and feedback mechanisms. The analog circuit employs a feedback path with a filter having a frequency response that is the inverse of the power amplifier's distortion characteristics, eliminating the need for complex digital processors while achieving comparable linearity correction.
Solution Approach 2:
The patent introduces an intermediate analog predistortion stage that processes the signal before it enters the power amplifier. This intermediate circuit applies predistortion through analog filtering and feedback, serving as a mediator between the digital baseband signal and the power amplifier, thereby reducing the computational burden on digital processors.
2Manufacturing precision
If deep memory DPD is implemented to address high-frequency memory effects, then distortion correction improves, but processing time and computational load increase
Solution Approach 1:
The patent implements continuous-time analog filtering in the feedback path, allowing the predistortion correction to occur continuously rather than in discrete computational steps. This continuous action eliminates processing delays associated with digital computation while maintaining effective correction of memory effects through the analog filter's frequency response characteristics.
3Manufacturing precision
If traditional DPD methods are used for phase and gain distortion correction, then linearity is improved, but system cost increases
Solution Approach 1:
The patent designs a universal analog predistortion circuit that simultaneously corrects both phase and gain distortions through a single feedback path. The filter in the feedback path is configured to provide inverse frequency response that addresses multiple distortion types concurrently, eliminating the need for separate correction circuits for phase and gain, thereby reducing overall system cost.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The APD system simplifies the burden on baseband processors and DPD circuitry, improving overall linearity and performance of power amplifiers by effectively addressing memory-induced distortions without the high complexity and cost associated with traditional DPD methods.
Implementation Method 1
utilizing varactors with s-shaped capacitance to correct phase and gain distortions
Data Source
AI summary
An analog predistortion system for power amplifiers is disclosed. In one aspect, the system may apply analog predistortion to offset memory effects that may occur as a function of frequencies that operate faster than time constants of the related circuits. In a particular aspect, the analog predistortion is applied at least to a phase of the signal to be amplified, but may also be applied to a gain of the signal to be amplified. When such memory focused analog predistortion is combined with memoryless or low depth memory digital predistortion, overall linearity and performance of the power amplifier is improved.