Class-D Amplifier Carrier Wave Shaping for Lower Harmonic Distortion
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Solution Overview
Problem
Conventional class-D amplifiers experience increased total harmonic distortion and varying open loop gain in the small signal region due to overlapping pulse width ranges of first and second pulses, leading to inefficient power consumption.
Innovation Solution
Implementing first and second carrier wave generators that produce periodic signals with non-linear gradients, and pulse width modulators that generate pulses with duty ratios less than 50% and linearly changing pulse width differences, to stabilize the input/output characteristic and reduce harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional linear gradient carrier waves are used in class-D amplifiers, then the amplifier operates efficiently in large signal regions, but the open loop gain varies in small signal regions causing increased total harmonic distortion
Solution Approach 1:
The patent applies parameter changes by modifying the gradient of the carrier wave signal in the pulse width modulator. Specifically, the gradient parameter is changed from linear to non-linear, where the gradient becomes smaller in small signal regions and larger in large signal regions. This parameter modification stabilizes the open loop gain in small signal regions, reducing total harmonic distortion without requiring additional hardware components.
2Loss of energy
If the pulse width ranges of first and second pulses overlap in small signal regions, then power consumption is reduced, but the open loop gain becomes non-uniform causing distortion
Solution Approach 1:
The patent changes the gradient parameter of the carrier wave to resolve the contradiction between power consumption and characteristic stability. By making the gradient smaller in small signal regions, the pulse width difference changes linearly with input signal, stabilizing open loop gain while maintaining the overlapping pulse width configuration that reduces power consumption.
Solution Approach 2:
The patent applies dynamics by making the carrier wave gradient dynamic rather than static. The gradient adapts based on the signal region: smaller in small signal regions to stabilize gain, and larger in large signal regions for efficient operation. This dynamic adjustment allows the system to maintain both low power consumption and stable characteristics across different operating conditions.
Data Source
AI summary
Pulse width modulators 131P and 131N respectively generate a first pulse Vp whose pulse width changes according to an input signal Vin based on the input signal Vin and a generated first carrier wave C1P, and a second pulse Vn whose pulse width changes according to the input signal Vin based on the input signal Vin and a generated second carrier wave C1N. Wherein due to the non-liner gradient in each of the generated first carrier wave C1P and the generated second carrier wave C1N and, duty ratio of each of the generated first pulse Vp and the generated second pulse Vn is less than 50% in a state where a value of the input signal is zero; and a difference between a pulse width of the first pulse Vp and a pulse width of the second pulse Vn linearly changes according to the input signal Vin.