Class-D Audio Amplifier Feedback for PWM Distortion Compensation
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Solution Overview
Problem
Class-D power amplifiers face issues with power supply noise rejection and distortion due to non-ideal power MOSFETs and mismatches in switching circuitry, particularly in half-bridge topologies, which degrade the quality of audio signals.
Innovation Solution
A high-performance class-D audio amplifier circuit is developed, incorporating a modulator circuit, driver control circuit, and feedback circuit that generates a drive signal with compensation for noise and distortion by selecting between different pulse signals based on a control signal, modulating the duty cycle to correct pulse width distortions, and using a low pass filter to remove noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If half-bridge topology is used for class-D amplifier, then device complexity is reduced, but power supply noise rejection performance deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the output signal is fed back to the input through a feedback network. This feedback loop allows the system to detect power supply noise that has coupled to the output and generate corrective signals to cancel out the noise, thereby improving power supply rejection ratio without changing the half-bridge topology structure.
Solution Approach 2:
The patent introduces an intermediary noise cancellation circuit that acts as a mediator between the power supply and the output stage. This circuit generates an inverted version of the power supply noise and injects it into the output path to cancel the harmful noise coupling, effectively addressing the PSRR issue while maintaining the simple half-bridge architecture.
2Object-affected harmful factors
If sigma delta modulator is used to suppress noise, then noise performance is improved, but distortion from non-ideal power MOSFETs and integrator time constant effects worsen
Solution Approach 1:
The patent employs feedback to detect and correct distortions generated by non-ideal power MOSFETs and integrator time constant effects. By monitoring the output signal and comparing it with the input, the system can identify distortion components and apply corrective actions through the feedback network, thereby reducing distortion while maintaining the noise suppression benefits of the sigma delta modulator.
Solution Approach 2:
The patent adjusts operating parameters such as switching frequency and modulator coefficients to optimize the trade-off between noise suppression and distortion. By dynamically changing these parameters based on operating conditions, the system can minimize the adverse effects of non-ideal power MOSFETs and integrator time constants while maintaining effective noise filtering.
3Object-affected harmful factors
If inductor current is used in output filtering, then noise filtering is improved, but pulse width stretching or shortening occurs
Solution Approach 1:
The patent uses feedback to detect pulse width distortion caused by inductor current effects in the output filter. The feedback network measures the actual pulse width and generates corrective signals to compensate for stretching or shortening, thereby maintaining accurate pulse width modulation while retaining the effective noise filtering provided by the inductor.
Solution Approach 2:
The patent applies preliminary compensation for inductor current effects by pre-adjusting the PWM signal characteristics before they reach the output filter. This preliminary action anticipates the pulse width distortion that will occur and counteracts it in advance, ensuring accurate pulse width delivery to the load while maintaining effective noise filtering.
Data Source
AI summary
The present disclosure provides a method and apparatus for high performance class D audio amplifier circuit that includes: a modulator circuit for receiving a PWM input signal and generating a control signal, a driver control circuit, a switching circuit, and a feedback circuit. The driver control circuit is adapted to generate a drive signal for the switching circuit. The driving signal provides compensation for noise and distortions in a PWM output signal at each cycle by selecting either a first pulse signal or a second pulse signal based on the information of the control signal.