Class-D Amplifier HPF Feedback for PWM Distortion Suppression
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Solution Overview
Problem
Conventional class-D amplifiers face challenges in reducing PWM-intermodulated distortion while maintaining low hardware complexity and addressing mass production and application corner conditions.
Innovation Solution
The proposed class-D amplifier configuration includes a loop filter and at least one high pass filter (HPF) circuit, which reduces or cancels high frequency components in the feedback signal, thereby minimizing PWM intermodulation distortion and total harmonic distortion (THD).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional class-D amplifier generates a compensation signal through an additional replicated circuit (including loop filter and PWM generator replicas), then the high frequency component can be reduced/canceled, but the hardware complexity becomes too high
Solution Approach 1:
The patent extracts only the essential high frequency filtering function from the complex replicated circuit, implementing it through a simplified high pass filter circuit that removes high frequency components from the feedback signal without requiring full loop filter and PWM generator replicas
Solution Approach 2:
Instead of copying the entire loop filter and PWM generator circuits, the patent creates a simplified copy that only replicates the high frequency filtering capability through a high pass filter, achieving the same distortion cancellation effect with reduced hardware
2Object-generated harmful factors
If a delay buffer is used to perform shift delay operation on the PWM generator signal, then the high frequency component can be reduced/canceled, but the system suffers from PVT variation (process, voltage, and temperature variation) making mass production difficult
Solution Approach 1:
The patent replaces the sensitive delay buffer with a robust high pass filter circuit that is insensitive to PVT variations, using simple RC components that can be easily manufactured with consistent characteristics across mass production
Solution Approach 2:
The patent changes the approach from time-domain manipulation (delay buffer) to frequency-domain filtering (high pass filter), transforming the solution from one sensitive to PVT variations to another that is inherently more stable across process, voltage, and temperature changes
3Device complexity
If the out-of-band loop attenuation is insufficient, then the circuit design is simpler, but the high frequency component intermodulates with the triangle wave signal causing PWM intermodulation distortion
Solution Approach 1:
The patent introduces a high pass filter as an intermediary component in the feedback path that specifically targets and removes high frequency components before they can intermodulate with the triangle wave signal, providing a simple yet effective solution without requiring complex loop attenuation design
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces or cancels PWM intermodulation distortion and improves THD, while maintaining low hardware complexity and ensuring ease of mass production by avoiding issues related to process, voltage, and temperature variations.
Implementation Method 1
the at least one HPF circuit is coupled between the first amplifier and the second amplifier, and is arranged to receive an amplifier output of the first amplifier, and generate and output the second amplifier input according to the amplifier output of the first amplifier
Data Source
AI summary
An audio amplifier includes a loop filter, at least one high pass filter (HPF) circuit, a pulse width modulation (PWM) generator, and a power stage. The loop filter is arranged to receive an audio signal and a feedback signal, and includes a first amplifier and a second amplifier, wherein the first amplifier has a first output node, and is arranged to process the audio signal and the feedback signal; the second amplifier has a first input node, and is arranged to receive a first amplifier input and a second amplifier input; and the first amplifier input is obtained from a signal path coupled between the first output node and the first input node. The at least one HPF circuit is coupled between the first amplifier and the second amplifier, and is arranged generate and output the second amplifier input according to an amplifier output of the first amplifier.