Class D Audio Amplifier PWM Layout for Low Crosstalk

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Solution Overview

Problem

Existing Class D amplifiers face issues with channel-to-channel crosstalk and instability due to varying load impedances, which affect audio quality and safety.

Innovation Solution

Implementing individual triangle ramp generators synchronized by a single digital clock, using diodes for noise isolation and DC servo circuits to maintain equal triangle wave durations, and employing load sensing to adjust duty cycles for safe operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a global triangle ramp generator is used for multi-channel amplification, then device complexity is reduced, but channel-to-channel crosstalk increases

Engineering Contradiction:

Improvetriangle ramp generator structureVSAvoidchannel-to-channel crosstalk

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent divides the global triangle ramp generator into individual local triangle ramp generators for each audio channel. Each channel receives its own synchronized triangle wave from its dedicated generator, eliminating the shared resource that causes crosstalk. The generators are synchronized through a single digital clock signal that controls all local generators, maintaining coordination while preventing interference between channels.

Inventive Principle:

Principle #1Segmentation

2Object-affected harmful factors

If individual triangle ramp generators are implemented for each channel, then channel isolation is improved, but device complexity increases

Engineering Contradiction:

Improvechannel isolationVSAvoidnumber of triangle ramp generators

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent employs DC servo circuits in each local triangle ramp generator that monitor and adjust the triangle wave characteristics to maintain equal positive and negative durations. This feedback mechanism ensures stable operation and prevents distortion while keeping each generator self-contained and synchronized to the common digital clock, balancing isolation benefits with controlled complexity.

Inventive Principle:

Principle #23Feedback

3Ease of operation

If fixed duty cycle operation is used, then amplifier operation is simplified, but safety under varying load impedances is compromised

Engineering Contradiction:

Improveamplifier controlVSAvoidsafe operation under varying loads

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent implements dynamic duty cycle adjustment through load sensing circuits that detect varying load impedances and automatically modify the PWM duty cycle accordingly. This allows the amplifier to adapt its operation in real-time to match the connected load conditions, ensuring safe operation across different speaker impedances while maintaining simplified control through automated adjustment rather than manual intervention.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUSRE50589E1Reduced crosstalk and matched output power class D audio amplifier with oppositely polarized triangle waves

Publication Date: 2025.09.16 CRESTRON ELECTRONICS INC

AI summary

A multi-channel Class D audio amplifier is provided to substantially reduce channel-to-channel crosstalk by employing in each channel a local triangle ramp generator controlled by a single global digital timing signal. The noise critical timing/integrating capacitor for the triangle ramp generator resides locally in each channel and adjacent to the PWM comparator of that channel and referenced to the local ground of that channel. The amplifier can also include a duty cycle limitation circuit to limit output power availability depending on the impedance of any attached loads (speakers).