Triangle Wave Generator Feedback 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 high noise content in the oscillator ramp input, which conventional negative feedback techniques cannot effectively mitigate due to low loop gain at high audio frequencies.
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 triangular waveform output, maintaining linearity without significant sacrifice.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional negative feedback techniques are used to reduce noise in Class D amplifier output, then output noise is reduced, but the effectiveness is limited due to low loop gain at high audio frequencies
Solution Approach 1:
The invention applies preliminary action by reducing audio noise at the oscillator ramp input stage before the noise propagates through the amplifier. The feedback network is configured to specifically target and reduce audio band noise at the triangle wave generator input, preventing noise amplification throughout the signal chain rather than attempting to correct it at the output stage.
Solution Approach 2:
The invention implements feedback by introducing a feedback network connected to the oscillator ramp input that samples the output signal and feeds it back to reduce audio band noise at the triangle wave generator input. This feedback path is specifically designed to operate in the audio frequency range where conventional feedback techniques are ineffective due to low loop gain.
2Object-affected harmful factors
If audio noise is reduced at the oscillator ramp input, then audio band noise content is reduced, but this requires a specialized feedback network configuration
Solution Approach 1:
The feedback network is designed to perform multiple functions: it provides DC balance for the triangle wave generator and simultaneously reduces audio band noise through its feedback path. This multi-functionality reduces the need for separate dedicated noise reduction circuitry, thereby limiting the increase in device complexity while achieving the desired noise reduction.
Solution Approach 2:
The feedback network utilizes parameter changes in the feedback path to achieve noise reduction. By configuring the feedback network to have specific gain characteristics in the audio frequency range and different characteristics at the switching frequency, the system can reduce audio noise while maintaining proper DC balance without requiring complex additional circuitry.
3Object-affected harmful factors
If feedback network is designed to reduce audio noise, then noise reduction is achieved, but there may be sacrifice in linearity of triangular waveform output
Solution Approach 1:
The feedback network is designed with local quality by having frequency-dependent gain characteristics. It provides high gain in the audio frequency range to reduce noise while providing different gain characteristics at the switching frequency to maintain triangle wave linearity. This localized optimization allows noise reduction without significant sacrifice in waveform precision.
Solution Approach 2:
The feedback network implements dynamics by adapting its gain characteristics across different frequency ranges. The network dynamically provides stronger feedback action in the audio band for noise reduction while providing appropriate feedback at the switching frequency to maintain proper triangle wave generation, thereby balancing noise reduction with linearity preservation.
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 which 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.