Feedback Clipping Circuit for Oversampled Audio Noise Shaping
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Solution Overview
Problem
Existing signal processing systems face challenges in clipping oversampled sigma-delta modulated signals without introducing noise in the frequency band of interest, particularly due to the need for low-pass filtering which increases system complexity.
Innovation Solution
A signal processor comprising a summer, limiter, and feedback circuit that adjusts and limits the input signal using threshold values and error signals to generate feedback, effectively shifting out-of-band noise out of the audio frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low-pass filter is used before the clipping stage to prevent in-band noise, then in-band noise is reduced, but system complexity increases
Solution Approach 1:
The patent applies preliminary noise shaping through oversampling before clipping. By shaping the noise spectrum in advance using a sigma-delta modulator, the out-of-band noise is pushed to higher frequencies before the clipping operation occurs, preventing in-band noise without requiring additional low-pass filtering stages.
Solution Approach 2:
The patent implements a feedback loop where the clipped signal is fed back through a noise shaper that subtracts the clipped portions from the original signal. This feedback mechanism actively cancels out the in-band noise components that would otherwise be introduced by clipping, resolving the contradiction between noise reduction and system simplicity.
2Manufacturing precision
If clipping is applied to a signal with significant out-of-band noise, then the signal is limited to quantization levels, but in-band noise is added
Solution Approach 1:
The patent performs noise shaping before clipping by oversampling the input signal through a sigma-delta modulator. This preliminary action shapes the noise spectrum so that quantization noise is pushed out of the band of interest, allowing subsequent clipping to occur without introducing significant in-band noise.
Solution Approach 2:
The patent converts the harmful effect of clipping-induced noise into a benefit by using feedback to reshape the noise spectrum. The clipped signal, which initially introduces noise, is fed back through a noise shaper that strategically places the noise energy in out-of-band frequencies, transforming the harmful in-band noise into beneficial out-of-band noise that can be filtered more easily.
3Object-affected harmful factors
If oversampling is used to improve noise spectrum, then noise distribution is improved in the range of interest, but system complexity increases
Solution Approach 1:
The patent combines multiple functions into a single integrated sigma-delta modulator structure that performs both oversampling and noise shaping simultaneously. This multi-functional approach achieves noise spectrum improvement without proportionally increasing system complexity, as the same hardware structure accomplishes both tasks that would otherwise require separate stages.
Solution Approach 2:
The patent uses feedback within the sigma-delta modulator to achieve noise shaping. The feedback loop continuously adjusts the quantization error to push noise energy to out-of-band frequencies, achieving superior noise spectrum characteristics without requiring additional complex filtering stages that would otherwise be needed.
Data Source
AI summary
A signal processor and a method for processing an input signal are presented. The signal processor is adapted to clip an oversampled input signal without introducing noise in the frequency band of interest. For instance, the signal processor may be used for clipping an acoustic signal. The signal processor includes a summer coupled to a limiter and to a feedback circuit. The summer is adapted to sum the input signal with at least one feedback signal to provide an adjusted signal. The limiter is adapted to compare the adjusted signal with a first threshold value and a second threshold value to provide a limited signal. The feedback circuit is adapted to calculate a difference between the limited signal and the adjusted signal, and to generate at least one feedback signal based on the difference.