Triangular Waveform 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, then some noise reduction is achieved, but the effectiveness is limited due to low loop gain at high audio frequencies
Solution Approach 1:
The patent applies preliminary action by reducing audio noise at the oscillator ramp input stage before the noise propagates through the amplifier circuit. The feedback network is configured to specifically target and reduce noise on the triangular waveform generator input, preventing noise amplification rather than attempting to correct it later in the signal path.
Solution Approach 2:
The patent implements a feedback network that feeds back a portion of the output signal to the inverting input of the triangular waveform generator. This feedback mechanism specifically targets audio band noise frequencies and reduces them through the feedback loop, achieving noise reduction where conventional techniques fail due to low loop gain.
2Object-affected harmful factors
If an active feedback network is added to reduce audio band noise, then noise content is reduced, but device complexity increases
Solution Approach 1:
The feedback network performs multiple functions: it reduces audio band noise, maintains DC balance, and preserves triangular waveform linearity. By designing the feedback network to achieve multiple objectives simultaneously, the patent reduces the need for additional separate circuits, thereby limiting the increase in device complexity while achieving noise reduction.
Solution Approach 2:
The feedback network acts as an intermediary element that mediates between the oscillator ramp input and the PWM output stage. It introduces a controlled feedback path that specifically addresses audio noise without requiring complete redesign of the amplifier architecture, thus adding minimal complexity while achieving the desired noise reduction.
3Object-affected harmful factors
If feedback network is used 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 local characteristics: it provides high gain at audio frequencies for noise reduction while maintaining low gain at the switching frequency to preserve waveform linearity. This frequency-selective feedback approach allows noise reduction in the audio band without compromising the overall triangular waveform accuracy.
Solution Approach 2:
The feedback network dynamically adjusts its gain characteristics based on frequency: high gain at audio frequencies for noise suppression, and low gain at switching frequencies for linearity preservation. This parameter variation with frequency allows the system to achieve noise reduction while maintaining waveform accuracy.
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 the Class D amplifier's output signal by minimizing distortion 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 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.