Class D Amplifier Control Loop With Second-Order Filter

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Solution Overview

Problem

Legacy Class D amplifiers with first-order filters in the control loop face limitations in achieving sufficient loop gain at low frequencies and effective noise reduction, particularly in maintaining signal integrity across a wide frequency range.

Innovation Solution

Incorporating a second-order filter in the control loop, specifically between the second control input and the control output, and utilizing a compensator that can be disabled during clipping modes to manage signal distortion and maintain desired frequency responses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a first-order filter is used in the control loop, then the device complexity is reduced, but the loop gain at low frequencies is insufficient

Engineering Contradiction:

Improvefilter orderVSAvoidloop gain at low frequencies

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent changes the filter order parameter from first-order to second-order in the control loop. This parameter change increases the loop gain at low frequencies while maintaining high-frequency noise attenuation, directly resolving the contradiction between device complexity and low-frequency loop gain performance.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If a higher-order filter is used in the control loop, then the high-frequency noise attenuation is improved, but the device complexity increases

Engineering Contradiction:

Improvehigh-frequency noiseVSAvoidfilter order

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent implements a second-order filter in the control loop, which provides improved high-frequency noise attenuation compared to first-order filters. The second-order configuration achieves better suppression of high-frequency components while maintaining reasonable circuit complexity through efficient topology design.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If the compensator is always active, then the signal distortion is reduced, but the stability deteriorates during clipping modes

Engineering Contradiction:

Improvesignal distortionVSAvoidstability during clipping

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The patent implements dynamic control of the compensator by selectively disabling it during clipping modes. This dynamic adjustment allows the compensator to reduce signal distortion during normal operation while being deactivated to maintain stability during clipping conditions, effectively resolving the contradiction between distortion reduction and stability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent uses feedback mechanisms to detect clipping conditions and control the compensator state accordingly. The feedback system monitors the amplifier operation and dynamically adjusts the compensator enable/disable state based on the operating condition, achieving both low distortion and high stability.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS11258411B2Amplifier with an at least second order filter in the control loop

Publication Date: 2022.02.22 PURIFI APS

AI summary

A Class D amplifier having an integrating primary amplifier with an internal feedback, the amplifier further comprising a feedback loop with a filter of at least second order.