Triangular Wave PWM Quantizer for Stable Gain Across Modes
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Solution Overview
Problem
Class-D amplifiers in personal audio devices face challenges in maintaining a fixed combined gain across different operating modes, leading to variations in ramp voltage swing range and associated slope, which can introduce sensitivity and design difficulties due to changes in speaker voltage.
Innovation Solution
The implementation of a PWM modulator with a triangular wave generator and a comparator, coupled with a polarity inversion circuit, allows for adjustable analog gain in the quantizer to compensate for changes in speaker voltage, maintaining a fixed combined gain and reducing ramp voltage swing range variation between modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the speaker voltage changes between operating modes, then the power amplifier can adapt to different power requirements, but the combined gain varies and ramp voltage swing range changes
Solution Approach 1:
The patent implements dynamic adjustment of the triangular wave slope by controlling the current source connected to the integrator. The slope adjustment circuit modifies the integrator current based on operating mode, thereby dynamically changing the ramp voltage swing range to compensate for speaker voltage changes and maintain stable combined gain across different power amplifier operating modes.
2Adaptability or versatility
If the ramp voltage swing range varies with speaker voltage, then the PWM modulator can operate at different voltage levels, but the slope variation introduces sensitivity and design difficulties
Solution Approach 1:
The patent employs feedback mechanisms where the adjusted triangular wave slope compensates for speaker voltage variations. The slope adjustment circuit receives feedback about the operating mode and相应ly modifies the integrator current to maintain optimal PWM modulation characteristics, reducing sensitivity to voltage variations and simplifying the overall design.
3Ease of manufacture
If the triangular wave slope is fixed, then the circuit design is simpler, but the gain calibration accuracy decreases when speaker voltage changes
Solution Approach 1:
The patent changes the parameter of triangular wave slope dynamically based on operating mode. By adjusting the integrator current in response to speaker voltage changes, the system maintains accurate gain calibration across different power amplifier modes while keeping the overall circuit structure relatively simple and manageable.
Data Source
AI summary
An apparatus in a PWM modulator includes a triangular wave generator that generates a triangular wave and a comparator that is responsive to a signal input to generate a signal output. An output of the PWM modulator is responsive to the comparator signal output. A polarity inversion circuit, coupled between the triangular wave generator and the comparator, is configured in one of the following ways: to provide the triangular wave to the comparator when the triangular wave has a first slope polarity and to provide a polarity-inverted version of the triangular wave to the comparator when the triangular wave has a second slope polarity opposite the first slope polarity; and to provide the signal input to the comparator when the triangular wave has the first slope polarity and to provide a polarity-inverted version of the signal input to the comparator when the triangular wave has the second slope polarity.