Class-D Amplifier PWM Circuit for High Power Supply Rejection
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Solution Overview
Problem
Class-D amplifiers with standard implementations often suffer from propagation delays and low power supply rejection ratios, which affect their efficiency and performance in applications like loudspeaker drivers.
Innovation Solution
A class-D amplifier design incorporating an integration stage, a comparison stage, and a full bridge circuit that generates a pulse width modulation signal using a ramp signal and a hysteretic signal, positioned at half the voltage level of the power supply, to drive the full bridge circuit, eliminating the need for an oscillator and ramp generator, and maintaining a constant gain independent of the power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If standard implementation of class-D amplifier is used, then high efficiency is achieved, but propagation delays and low power supply rejection ratios occur
Solution Approach 1:
The patent changes the operating parameters by positioning the ramp signal and hysteretic signal at half the voltage level of the power supply, and uses an integration stage to generate a ramp signal that is independent of power supply variations. This parameter transformation resolves the contradiction by making the amplifier's gain independent of power supply voltage while maintaining high efficiency class-D operation.
Solution Approach 2:
The integration stage acts as an intermediary between the input signal and the pulse width modulation generation. It generates a ramp signal that serves as a reference for comparison with the hysteretic signal, thereby eliminating direct dependence on power supply voltage and improving power supply rejection ratio while maintaining efficient switching operation.
2Loss of energy
If standard implementation of class-D amplifier is used, then high efficiency is achieved, but propagation delays occur
Solution Approach 1:
The integration stage generates the ramp signal in advance as a continuous function of time, independent of the switching operation. This preliminary preparation of the ramp signal allows for immediate comparison with the hysteretic signal without additional propagation delays, while the class-D switching architecture maintains high efficiency.
3Measurement precision
If oscillator and ramp generator are included, then accurate pulse width modulation is achieved, but device complexity increases
Solution Approach 1:
The patent merges the ramp generator function into the integration stage, which also serves as part of the pulse width modulation circuit. The integration stage simultaneously performs signal integration, ramp generation, and provides the reference signal for PWM comparison, eliminating the need for separate oscillator and ramp generator circuits while maintaining accurate pulse width modulation.
Solution Approach 2:
The integration stage is designed to perform multiple functions: it integrates the input signal, generates the ramp signal, and provides the reference for PWM comparison. This multi-functional design achieves accurate pulse width modulation without increasing device complexity, as one circuit element serves multiple purposes in the signal processing chain.
Data Source
AI summary
An amplifier that receives an input signal and outputs an amplified output signal includes an integration stage, a comparison stage, and a full bridge circuit. The integration stage is be used for receiving a constant common mode voltage, for receiving a first signal representing the input signal of the amplifier, and for generating a ramp signal. The comparison stage coupled to the integration stage is used for generating a pulse width modulation signal according to the ramp signal and according to a hysteretic signal. The full bridge circuit coupled to the comparison stage is used for receiving a power supply and the pulse width modulation signal, and for generating the output of the amplifier.