Intersample Amplitude Limiting for Overshoot-Safe Signal Chains
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Solution Overview
Problem
Amplitude overshoot occurs in signal processing systems due to band limiting, interpolation, and DAC conversion, leading to signal distortions and artifacts in downstream devices like PWM amplifiers, which existing methods like attenuation gain and low-threshold clipping inadequately address.
Innovation Solution
A signal processing method using sub-filters to predict intersample behavior, replacing input samples with reduced samples of the same sign but lower magnitude, based on parameters of the subsequent device, to prevent overshoot, with optional smoothing steps to correct distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If attenuation gain or low-threshold clipping is applied to all input samples, then amplitude overshoot is reduced, but the usable output amplitude range is severely reduced
Solution Approach 1:
The patent predicts intersample values in advance using sub-filters before the main filtering operation, allowing proactive adjustment of input samples to prevent overshoot. This preliminary prediction and correction approach avoids the need for severe attenuation of all samples, thereby maintaining larger usable output amplitude range while still preventing overshoot.
Solution Approach 2:
Instead of applying uniform attenuation to all input samples, the patent applies localized correction only to specific samples that are predicted to cause intersample overshoot. The limiting operation is selectively applied based on the predicted intersample behavior, preserving the amplitude of samples that do not pose an overshoot risk and thus maintaining greater output dynamic range.
2Manufacturing precision
If band limiting or interpolation is applied to a discrete-time signal, then signal quality is improved, but amplitude overshoot occurs at the output
Solution Approach 1:
The patent performs preliminary prediction of intersample values using sub-filters before the main band limiting or interpolation operation. This allows the system to identify and correct input samples that would lead to overshoot, enabling the subsequent filtering to produce high-quality output without amplitude overshoot artifacts.
Solution Approach 2:
The patent uses a feedback mechanism where predicted intersample values are compared against threshold limits, and correction decisions are made based on this comparison. The limiting operation is applied adaptively based on the predicted behavior, creating a closed-loop system that ensures output samples remain within acceptable amplitude bounds while maintaining signal quality.
3Reliability
If clipping is applied to prevent overshoot, then amplitude control is improved, but ringing artifacts occur due to the Gibbs phenomenon
Solution Approach 1:
The patent applies clipping or limiting in advance to predicted input samples before they undergo band limiting or interpolation. By pre-correcting the input samples based on intersample predictions, the subsequent filtering operations do not encounter abrupt discontinuities that would generate ringing artifacts, thus maintaining amplitude control while avoiding Gibbs phenomenon.
Solution Approach 2:
The patent takes preliminary anti-action by predicting and preventing the conditions that would lead to ringing artifacts. Instead of allowing clipped samples to pass through the filtering process (which would create ringing), the system proactively adjusts the input samples to prevent the formation of discontinuities that trigger the Gibbs phenomenon, thereby eliminating the root cause of ringing rather than treating its symptoms.
Data Source
AI summary
A method comprising: receiving and clipping input samples of a signal to be processed by a subsequent device; performing a limiting step on at least one input sample; wherein the limiting step includes: generating predicted intersample values by applying sub-filters to corresponding pluralities of input samples including the concerned input sample, wherein the sub-filters model the intersample behavior of the subsequent device; and replacing the concerned input sample with a reduced sample by applying an offset to the concerned input sample; wherein the reduced sample has the same sign, but a lower magnitude than the concerned input sample; wherein the offset is computed based on parameters of the sub-filters and an overshoot difference between a threshold and one of the predicted intersample values.