Triangular Waveform Generator With Feedback for Low Audio 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 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 and method incorporating an active integrator and an active feedback network that reduces audio band noise content, utilizing a square waveform clock circuit and operatively coupling an active feedback network to the integrator to achieve low noise output without compromising linearity.
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, then noise reduction is attempted, but the low loop gain at high audio bandwidth limits the effectiveness
Solution Approach 1:
The patent applies feedback by feeding back a portion of the output signal to the inverting input of the integrator. This feedback mechanism directly addresses the noise problem by reducing audio band noise in the triangular waveform output, overcoming the limitation of conventional negative feedback techniques that suffer from low loop gain at high audio bandwidth.
2Object-affected harmful factors
If feedback network is added to reduce noise, then audio band noise is reduced, but linearity of triangular waveform may be compromised
Solution Approach 1:
The feedback network is designed with specific parameters including resistors R1, R2, R3, R4 and capacitors C1, C2 with carefully selected values. The transfer function shows poles and zeros at specific frequencies to shape the feedback gain, reducing noise in audio band while maintaining linearity of the triangular waveform output.
3Object-affected harmful factors
If feedback network is designed to reduce noise, then audio noise is reduced, but DC balance and stability must be maintained
Solution Approach 1:
The feedback network provides different feedback gains at different frequency ranges. At DC and low frequencies, the feedback gain is designed to maintain DC balance and stability, while at audio frequencies, the feedback gain is optimized for noise reduction. This frequency-dependent local quality approach resolves the contradiction between noise reduction and stability maintenance.
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 significantly reduces audio band noise in the triangular waveform output, improving the quality of the Class D amplifier's output by maintaining linearity and stability, and is 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
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AI summary
A triangular waveform generator includes a square waveform clock circuit and an active integrator. The active integrator receives input from the square waveform clock circuit and generates a triangular waveform output. An active feedback network is operatively added to the active integrator to reduce the audio band noise content in the triangular waveform output. The feedback network acts as a DC balance without significant sacrifice in the linearity of the triangular waveform output.