Class-D Amplifier PWM Common-Mode Control for High PSRR
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Solution Overview
Problem
Class-D amplifiers face efficiency losses due to the use of low-dropout regulators, which reduce energy efficiency and introduce noise, necessitating a design with high power-supply rejection ratio (PSRR) and low Total Harmonic Distortion with Noise (THD+N) without relying on these regulators.
Innovation Solution
A class-D amplifier design incorporating pulse-width modulation (PWM) common-mode control, featuring a loop filter, PWM circuit, output circuit, and common-mode control circuit to suppress supply noise and even harmonic distortions, improving PSRR and linearity by monitoring and adjusting the common-mode level of the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-dropout regulator is used to supply clean power to the class-D amplifier, then power supply rejection ratio is improved, but energy efficiency deteriorates due to additional power loss
Solution Approach 1:
The patent extracts and removes the low-dropout regulator from the power supply chain of the class-D amplifier. Instead of using an LDO to regulate the power supply, the invention directly powers the amplifier from the battery, eliminating the regulator and its associated power losses while maintaining high PSRR through the amplifier's intrinsic design
Solution Approach 2:
The class-D amplifier is designed to be self-sufficient in rejecting power supply noise without requiring an external LDO regulator. The amplifier's internal architecture, including its PWM modulator and feedback circuitry, inherently provides high power supply rejection, making the system self-service in maintaining clean power operation
2Object-affected harmful factors
If a low-dropout regulator is used to mitigate noise coupling, then noise rejection is improved, but Total Harmonic Distortion with Noise increases due to reduced linearity
Solution Approach 1:
The patent employs a feedback circuit that monitors the output signal and feeds it back to the input stage. This feedback mechanism corrects non-linearities and reduces Total Harmonic Distortion with Noise, improving linearity without requiring an LDO regulator. The feedback loop actively compensates for distortion components, maintaining high audio fidelity
3Loss of energy
If power is supplied directly from battery without LDO, then energy efficiency is improved, but power supply rejection ratio deteriorates
Solution Approach 1:
The patent changes the operating parameters of the class-D amplifier, specifically optimizing the PWM switching frequency and duty cycle control. By carefully selecting and adjusting these parameters, the amplifier achieves high power supply rejection ratio while operating directly from the battery without an LDO, maintaining both energy efficiency and noise rejection
Data Source
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AI summary
A class-D amplifier (100, 300, 1200) includes a loop filter (102), a pulse-width modulation (PWM) circuit, an output circuit (106), and a common-mode control circuit (302, 500). The loop filter (102) receives an input signal (VIN) of the class-D amplifier (100, 300, 1200) to generate a filtered signal (VLF). The PWM circuit (106) converts a non-PWM signal (VSUM) into a PWM signal (VPWM), wherein the non-PWM signal (VSUM) is derived from at least the filtered signal (VLF). The output circuit (106) generates an output signal (VOUT) of the class-D amplifier (100, 300, 1200) according to the PWM signal (VPWM). The common-mode control circuit (302, 500) monitors a common-mode level of the output signal (VOUT) to generate a common-mode control signal (VCM_CTRL) for PWM common-mode control.