Mixed-Mode Digital Predistortion for Wideband Harmonic Correction
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Solution Overview
Problem
Power amplifier circuits operating in nonlinear regions face challenges with wideband input signals, leading to increased distortion and noise, as predistortion compensation methods struggle to correct distortion terms across a wide frequency band without degrading the input signal.
Innovation Solution
A mixed-mode digital predistortion (DPD) circuit is employed, comprising a linear DPD circuit for complex mode processing and a nonlinear DPD circuit for real mode processing, which converts complex baseband signals to real signals, allowing for correction of distortion terms at the carrier frequency and harmonics, and utilizing look-up tables or FIR filters for distortion compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If predistortion compensation is used to correct distortion in nonlinear PA operation, then amplifier efficiency is improved, but distortion terms at carrier frequency harmonics cannot be effectively removed without degrading wideband input signals
Solution Approach 1:
The predistortion system is divided into multiple independent predistorter circuits, each responsible for correcting distortion at specific harmonic frequencies. The first predistorter corrects fundamental frequency distortion while the second predistorter corrects second harmonic distortion, and so on. This segmentation allows each predistorter to target specific distortion terms without interfering with wideband input signals, resolving the contradiction between efficiency improvement and harmonic distortion removal.
2Object-generated harmful factors
If low-pass filtering is used to remove distortion terms at carrier frequency harmonics, then distortion is reduced, but wideband input signals are degraded
Solution Approach 1:
Instead of using low-pass filtering that directly affects the wideband signal, the patent introduces predistorter circuits as intermediary elements that pre-compensate distortion before the signal reaches the power amplifier. These predistorters modify the input signal to counteract the nonlinear distortion that will be generated, allowing distortion removal without degrading the wideband input signal integrity.
3Use of energy by moving object
If PA circuit operates in nonlinear region to improve efficiency, then power consumption is reduced, but signal distortion increases
Solution Approach 1:
The predistorter circuits perform preliminary distortion compensation on the input signal before it enters the nonlinear power amplifier region. By pre-applying the inverse of the expected distortion, the system allows the PA to operate efficiently in its nonlinear region while the preliminary predistortion action ensures that the final output signal remains clean with minimal distortion.
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AI summary
Various examples are directed to systems and methods for digital predistortion (DPD). A linear digital predistortion (DPD) circuit may be programmed to generate a pre-distorted signal linear component based at least in part on a complex baseband signal. A nonlinear DPD circuit may be programmed to generate a pre-distorted signal nonlinear component based at least in part on the complex baseband signal. A mixer circuit programmed to generate a pre-distorted signal based at least in part on the pre-distorted signal linear component and the pre-distorted signal nonlinear component.