Single-Ended Class-D PWM Amplifier Feedback for Distortion Reduction

Solution Overview

Problem

Single-ended output class-D pulse width modulation amplifiers suffer from total harmonic distortion and power supply intermodulation distortion due to common-mode current flow, which degrades audio signal quality in personal audio devices.

Innovation Solution

The proposed solution involves a system with a first stage for differential pulse-width modulation input signal processing, a quantizer, a single-ended class-D output stage, a feedback network, and buffering and biasing subcircuits to minimize distortion by equalizing impedances and reducing common-mode current effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single-ended output class-D amplifier is used to reduce area and component count, then device complexity is reduced, but total harmonic distortion and power supply intermodulation distortion increase due to common-mode current flow

Engineering Contradiction:

Improveamplifier structureVSAvoidsignal quality

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The amplifier is divided into two separate output drivers (first output driver and second output driver) that each drive separate output terminals. This segmentation allows the common-mode currents to flow through separate paths, preventing them from interacting with the feedback network and causing distortion.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A feedback network is introduced as an intermediary component that selectively feeds back only the differential-mode signal while rejecting common-mode signals. The feedback network includes resistors configured to sum the outputs and feed back only the differential component, effectively filtering out the harmful common-mode currents before they can cause distortion.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Area of stationary object

If a single-ended output class-D amplifier is used to reduce area, then area consumption is reduced, but audio signal quality degrades due to common-mode current effects

Engineering Contradiction:

Improveamplifier areaVSAvoidaudio signal quality

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The amplifier is divided into two separate output drivers (first output driver and second output driver) that each drive separate output terminals. This segmentation allows the common-mode currents to flow through separate paths, preventing them from interacting with the feedback network and causing distortion.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A feedback network is introduced as an intermediary component that selectively feeds back only the differential-mode signal while rejecting common-mode signals. The feedback network includes resistors configured to sum the outputs and feed back only the differential component, effectively filtering out the harmful common-mode currents before they can cause distortion.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of operation

If common-mode current flow is allowed in single-ended output class-D amplifier, then circuit operation is simplified, but power supply induced intermodulation distortion occurs

Engineering Contradiction:

Improvecircuit operationVSAvoidintermodulation distortion

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

A feedback network is introduced as an intermediary component that selectively feeds back only the differential-mode signal while rejecting common-mode signals. The feedback network includes resistors configured to sum the outputs and feed back only the differential component, effectively filtering out the harmful common-mode currents before they can cause distortion.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The feedback network provides negative feedback that actively counteracts common-mode current effects. By feeding back only the differential signal and not the common-mode signal, the system continuously corrects for any common-mode disturbances, preventing intermodulation distortion while maintaining simplified operation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS12113488B2Minimizing total harmonic distortion and power supply induced intermodulation distortion in a single-ended class-D pulse width modulation amplifier

Publication Date: 2024.10.08 CIRRUS LOGIC INC

AI summary

An amplifier system may include a first stage having a plurality of inputs configured to receive a differential pulse-width modulation input signal and generate an intermediate signal based on the differential pulse-width modulation input signal, a quantizer configured to generate a modulated signal based on the intermediate signal, a single-ended class-D output stage configured to generate a single-ended output signal as a function of the differential pulse-width modulation input signal, a feedback network configured to feed back the single-ended output signal to a first input of the plurality of inputs and to feed back a ground voltage to a second input of the plurality of inputs, a plurality of buffers, each particular buffer configured to receive a respective component of the differential pulse-width modulation input signal and generate a respective buffered component, and an input network coupled between the plurality of buffers and the first stage. Each particular buffer of the plurality of buffers may include a buffering subcircuit configured to buffer the respective component of the differential pulse-width modulation input signal associated with the particular buffer in order to generate the respective buffered component and a biasing subcircuit configured to limit a magnitude of the respective component of the differential pulse-width modulation input signal driven to circuitry of the buffering subcircuit for driving the respective buffered component.