Class-D Audio Amplifier Half-Swing PWM EMI Reduction
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Solution Overview
Problem
Class-D amplifiers with ternary PWM coding face challenges in reducing electromagnetic interference (EMI) and requiring complex logic modules for encoding, which increases device complexity and power consumption.
Innovation Solution
A Class-D audio amplifier using a half-swing modulation signal to generate PWM control signals, allowing direct ternary encoding without additional logic circuits, thereby reducing EMI and complexity while maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ternary PWM coding is used to reduce EMI in filterless Class-D amplifiers, then EMI performance is improved, but device complexity increases due to the requirement of additional logic modules for encoding
Solution Approach 1:
The patent extracts and eliminates the complex ternary logic encoding module from the amplifier circuit. Instead of using traditional ternary PWM coding that requires logic modules to encode 4-state switching signals to three-state signals, the invention directly generates ternary-encoded PWM signals through a simplified comparator-based modulation scheme, removing the harmful complexity while maintaining EMI reduction benefits
Solution Approach 2:
The patent changes the modulation signal parameter from traditional full-swing to half-swing PWM. By using a half-swing modulation signal with reduced amplitude, the invention achieves ternary encoding directly at the output stage without requiring additional logic encoding circuits, thus reducing EMI while simplifying the device structure
2Volume of stationary object
If filterless Class-D operation is implemented to reduce system size and cost, then system size and cost are reduced, but EMI radiation increases
Solution Approach 1:
The patent employs half-swing PWM modulation as a parameter change technique. By reducing the modulation signal amplitude to half of the traditional full-swing approach, the invention achieves ternary encoding that radiates less EMI while maintaining the filterless compact design, thus resolving the contradiction between small system size and low EMI radiation
Solution Approach 2:
The patent converts the potential harm of filterless operation (increased EMI radiation) into a benefit by implementing ternary PWM coding through half-swing modulation. This approach transforms the EMI issue into an opportunity to achieve both compact size and reduced electromagnetic interference by directly generating ternary-encoded signals without requiring additional filtering components
Data Source
AI summary
An amplifier includes a first comparator, a second comparator, and an output switch. The first and second comparators respectively compare a pair of differential signals with a half-swing modulation signal to generate first and second pulse-width-modulation (PWM) control signals, wherein a voltage swing of the half-swing modulation signal is smaller than voltage swing of the differential signals. The output switch includes a pair of inputs coupled to receive the PWM control signals to provide a ternary encoded output signal in response to the PWM control signals.