Two-Stage Sigma-Delta Audio Amplifier for Low-Impedance Loads
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Solution Overview
Problem
Conventional class-D audio amplifiers face issues with saturation and high power consumption when driving low-impedance loads, leading to distorted audio signals and voltage drops in power supplies, while multi-level output modulators offer better linearity but at the cost of increased complexity and power usage.
Innovation Solution
An audio amplifier design incorporating a high-order sigma-delta modulator followed by a lower-order sigma-delta modulator, where the first modulator generates a multi-level output with more than three levels and the second modulator reduces levels to two or three, operating at a higher sampling frequency, drives an H-bridge circuit coupled to speakers, thereby reducing saturation and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-order multi-level sigma-delta modulator is used, then linearity is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent divides the modulation function into two separate stages: a first sigma-delta modulator that performs noise shaping and generates a multi-level digital signal, and a second modulator stage that converts it to the final pulse density output. This segmentation allows each stage to be optimized independently, achieving high linearity without requiring a single complex high-order modulator.
Solution Approach 2:
The first sigma-delta modulator acts as an intermediary between the input audio signal and the final output, generating a multi-level digital signal that serves as an intermediate representation. This intermediate signal contains the noise-shaped quantization error that is then processed by the second modulator stage, allowing complex noise shaping without direct complexity in the final modulation stage.
2Measurement precision
If a multi-level output modulator is used, then linearity is improved, but power consumption increases
Solution Approach 1:
The patent changes the parameter of output signal levels dynamically through the two-stage modulation process. The first modulator operates with multiple voltage levels for high linearity, while the second stage converts this to a simplified two-level or three-level pulse density signal. This parameter transformation allows the system to achieve high linearity during intermediate processing while maintaining low power consumption at the final output stage.
3Use of energy by moving object
If switching power output stages are used, then efficiency is improved, but saturation and distortion occur when driving low-impedance loads
Solution Approach 1:
The patent implements feedback through the sigma-delta modulation process, where quantization error is fed back and shaped in the frequency domain. This feedback mechanism allows the switching output stage to operate with high efficiency while the noise-shaped quantization error prevents saturation and distortion, maintaining signal quality even when driving low-impedance loads.
Data Source
AI summary
According to an aspect, an audio amplifier includes a first sigma-delta modulator configured to receive a digital audio signal and generate a first multi-level output signal based on the audio signal, and a second sigma-delta modulator configured to receive the first multi-level output signal from the first sigma-delta modulator and generate a second multi-level output signal. The second multi-level output signal has a number of levels less than a number of levels of the first multi-level output signal.