PCM to PWM Predistortion for Harmonic Reduction
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Solution Overview
Problem
The conversion of PCM to PWM signals is computationally intensive due to high complexity in natural sampling and quantization, particularly with techniques like Integral Noise Shaping, which require significant computational resources.
Innovation Solution
A predistortion approach is implemented, using Second and Third Harmonic Nonlinear Functions to estimate and correct nonlinearities in the PWM process, resulting in a PCM predistorted signal that improves linearity and eliminates harmonics, thereby simplifying the conversion process and reducing computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If natural sampling is used for PCM to PWM conversion, then the conversion method is simple, but the computational complexity is very high
Solution Approach 1:
The patent applies preliminary action by performing predistortion processing on the PCM signal before PWM conversion. The predistortion filter pre-compensates for nonlinearities and harmonics, so that the subsequent natural sampling and quantization processes produce accurate PWM output without requiring complex computational corrections during the main conversion process.
Solution Approach 2:
The patent segments the PCM to PWM conversion process into distinct functional blocks: predistortion filtering, natural sampling, quantization, and PWM generation. This segmentation allows each stage to be optimized independently, with the predistortion stage handling nonlinear compensation and the natural sampling stage handling the core conversion with minimal computation.
2Measurement precision
If quantization of PWM is performed, then the PWM signal accuracy is improved, but the computational complexity increases significantly
Solution Approach 1:
The predistortion filter performs preliminary compensation for quantization errors and nonlinearities before the quantization stage. By pre-shaping the signal spectrum and removing harmonics in advance, the quantization process requires fewer iterative corrections and achieves accurate PWM output with reduced computational burden.
3Reliability
If Integral Noise Shaping is used, then noise shaping for PWM signals is achieved, but the computational complexity is significant
Solution Approach 1:
The patent extracts the noise shaping function from the main PWM conversion loop and implements it through a dedicated predistortion filter that operates in parallel. This separate noise shaping stage processes the PCM signal independently before conversion, eliminating the need for complex iterative noise shaping calculations during the PWM generation process.
4Manufacturing precision
If predistortion is applied to correct PWM nonlinearity, then harmonic distortion is reduced, but the processing steps increase
Solution Approach 1:
The patent merges the predistortion filtering function with the existing PCM to PWM conversion architecture by integrating it as a preprocessing stage. The predistortion filter combines multiple compensation functions (nonlinearity correction, harmonic removal, noise shaping) into a single unified processing block that operates before the main conversion pipeline, reducing the need for separate correction stages.
Data Source
AI summary
A PCM signal is converted to a PWM signal using predistortion to alleviate harmonics. A PCM predistorted signal is converted to the PWM and amplified. A third harmonic nonlinear function receives the PCM signal and produces a third harmonic of the PCM signal. A third harmonic difference function takes one sixth of the third harmonic and produces a third harmonic PCM compensation signal. The PCM signal and the third harmonic PCM compensation signal are summed to produce a PCM predistorted signal for a full-bridge amplifier. A second harmonic nonlinear function produces a second harmonic of the PCM signal. A second harmonic function takes one fourth of the second harmonic to produce a second harmonic PCM compensation signal. The PCM signal, the third harmonic PCM compensation signal, and the second harmonic PCM compensation signal are summed to produce the PCM predistorted signal for a half-bridge amplifier.