PWM Audio Amplifier Feedback Loops for Phase-Stable Fidelity

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Solution Overview

Problem

Wearable audio devices face challenges in achieving high-fidelity audio reproduction while operating in a power-efficient manner due to limited battery capacity and size constraints.

Innovation Solution

An audio amplifier with a feedback circuit comprising a high bandwidth input common mode loop and a low bandwidth output common mode loop, configured to provide a desired phase change, is implemented using pulse width modulation to enhance audio performance and efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If pulse width modulation is used for amplification, then power efficiency is improved, but audio fidelity may deteriorate

Engineering Contradiction:

Improvepower efficiencyVSAvoidaudio fidelity

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The patent implements a feedback circuit that samples the output signal and feeds it back to the input stage. This closed-loop feedback mechanism corrects distortion introduced by PWM switching, enabling high power efficiency while maintaining audio fidelity through continuous error correction.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent employs multiple PWM frequencies that can be dynamically switched based on signal characteristics. By changing the modulation frequency parameter, the system optimizes between power efficiency and audio quality requirements for different operating conditions.

Inventive Principle:

Principle #35Parameter changes

2Speed

If high bandwidth input common mode loop is used, then regulation speed is improved, but phase stability deteriorates

Engineering Contradiction:

Improveregulation speedVSAvoidphase stability

Core Design Contradiction:

SpeedVSStability of the object's composition

Solution Approach 1:

The patent divides the common mode regulation into two separate loops: a high bandwidth input common mode loop for fast transient response, and a low bandwidth output common mode loop for phase stability. This segmentation allows each loop to be optimized for its specific function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary capacitive coupling between the input and output common mode loops. This intermediary element transfers necessary signal information while isolating the two loops' frequency responses, enabling the high bandwidth loop to operate fast without destabilizing the overall phase response.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12512798B2Pulse-width modulation audio amplifier having compensated regulation loop

Publication Date: 2025.12.30 SKYWORKS SOLUTIONS INC

AI summary

In some embodiments, an audio amplifier can include an input for receiving a signal to be amplified, and an amplification stage configured to amplify the signal based on pulse width modulation and provide the amplified signal at an output node. The audio amplifier can further include a feedback circuit implemented between the output node and the input node. The feedback circuit can include a series arrangement of a high bandwidth input common mode loop and a low bandwidth output common mode loop, with the low bandwidth output common mode loop configured to provide a desired phase change for the high bandwidth input common mode loop.