Class-D Amplifier PWM Output Shorting for EMI Reduction

Solution Overview

Problem

Prior class-D amplifiers suffer from significant electromagnetic interference (EMI) due to switching, which interferes with the operation of other electronic elements.

Innovation Solution

A class-D amplifier configuration that includes a PWM circuit with an H-Bridge driver and a control circuit using PWM signals to differentially drive a load, reducing EMI by shorting outputs together in specific states, thereby minimizing voltage swing and associated EMI.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If prior class-D amplifiers use digital switching to convert analog signal to digital signal, then the amplifier can achieve digital signal processing capability, but electromagnetic interference is generated which interferes with other electronic elements

Engineering Contradiction:

Improvedigital signal processing capabilityVSAvoidelectromagnetic interference

Core Design Contradiction:

Extent of automationVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful electromagnetic interference generated by digital switching into a beneficial effect by using the switching action to actively short outputs together during specific states. The same switching mechanism that causes EMI is now used to minimize voltage swing and reduce EMI radiation, transforming the harmful effect into a solution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the voltage swing parameter by dynamically adjusting output levels through controlled shorting. By modifying the voltage swing parameter to be minimal during certain operating states, the patent reduces electromagnetic interference while maintaining digital signal processing functionality.

Inventive Principle:

Principle #35Parameter changes

2Extent of automation

If class-D amplifier uses switching operation to convert analog signal to digital signal, then digital signal processing is enabled, but voltage swing generates electromagnetic interference

Engineering Contradiction:

Improvesignal conversion capabilityVSAvoidelectromagnetic interference affecting other elements

Core Design Contradiction:

Extent of automationVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful electromagnetic interference generated by digital switching into a beneficial effect by using the switching action to actively short outputs together during specific states. The same switching mechanism that causes EMI is now used to minimize voltage swing and reduce EMI radiation, transforming the harmful effect into a solution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the voltage swing parameter by dynamically adjusting output levels through controlled shorting. By modifying the voltage swing parameter to be minimal during certain operating states, the patent reduces electromagnetic interference while maintaining digital signal processing functionality.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If amplifier switches load with digital switches, then digital control is achieved, but electromagnetic interference interferes with operation of other electronic elements

Engineering Contradiction:

Improvedigital control capabilityVSAvoidoperation stability of other electronic elements

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent converts the harmful electromagnetic interference generated by digital switching into a beneficial effect by using the switching action to actively short outputs together during specific states. The same switching mechanism that causes EMI is now used to minimize voltage swing and reduce EMI radiation, transforming the harmful effect into a solution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the voltage swing parameter by dynamically adjusting output levels through controlled shorting. By modifying the voltage swing parameter to be minimal during certain operating states, the patent reduces electromagnetic interference while maintaining digital signal processing functionality.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7852155B2Class-D amplifier and method therefor

Publication Date: 2010.12.14 SEMICON COMPONENTS IND LLC

AI summary

In one embodiment, a class-D amplifier (11) is configured to form first (DP) and second (DN) PWM signals each having a duty cycle that is proportional to a received analog input signal (12) and responsively to enable a switch (31, 32) to short the outputs (13, 14) of the class-D amplifier (11) together responsively to some states of the first (DP) and second (DN) PWM signals.