Triangular Waveform Feedback Circuit for Low Audio Band Noise
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Solution Overview
Problem
Class D audio amplifiers generate PWM output signals with undesirable spectral components and audio band noise due to the reproduction of noise present in the triangular wave, which conventional negative feedback techniques fail to effectively reduce, especially at high audio bandwidths.
Innovation Solution
A triangular waveform generating apparatus comprising a square waveform clock circuit, an active integrator, and an active feedback network that reduces audio band noise content in the output, maintaining linearity and acting as a DC balance without significant sacrifice in output quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional negative feedback techniques are used to reduce noise, then noise reduction is attempted, but the loop gain is low at high audio bandwidth which limits effectiveness
Solution Approach 1:
The patent applies preliminary action by filtering the triangular wave signal before it is used in the PWM modulation process. An RC low-pass filter is applied to the triangular wave to remove high-frequency noise components before the signal reaches the comparator, preventing the noise from being reproduced in the output. This proactive approach is more effective than attempting to reduce noise through feedback after the fact, especially at high audio bandwidths where feedback effectiveness is limited.
2Object-affected harmful factors
If filtering is applied to reduce noise, then audio band noise is reduced, but linearity of the triangular waveform may be compromised
Solution Approach 1:
The patent applies local quality by selectively filtering only the high-frequency noise components of the triangular wave while preserving the fundamental waveform characteristics. The RC low-pass filter is designed with a cutoff frequency that allows the audio band signal to pass through while attenuating the ultrasonic switching frequency and its harmonics. This localized filtering approach reduces noise without significantly compromising the linearity of the triangular waveform.
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 solution effectively reduces audio band noise in the triangular waveform output, improving the quality of Class D amplifier outputs by minimizing noise reproduction and maintaining linearity, suitable for use in Class D amplifiers and other applications.
Implementation Method 1
an active integrator receives input from the square waveform clock circuit and generates a triangular waveform output
Implementation Method 2
An active feedback network is operatively added to the active integrator to reduce the audio band noise content in the triangular waveform output
Data Source
AI summary
A triangular waveform generator includes a square waveform clock circuit and an integrating circuit. The integration circuit receives input from the square waveform clock circuit and generates a triangular waveform output. A feedback circuit is operatively connected to the integrating circuit to reduce the audio band noise content in the triangular waveform output. The feedback circuit acts as a DC balance without significant sacrifice in the linearity of the triangular waveform output.