Modulator Circuit Feedback Filtering for Class-D Noise Control

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Solution Overview

Problem

Class-D amplifiers require high-performance components to handle high-frequency noise and residual modulation tones, leading to increased circuit size and power consumption due to the need for precise matching of feedback and feedforward signals.

Innovation Solution

A modulator circuit with low-pass filtering and phase lead compensation is implemented, using compensation signals derived from unfiltered feedback and feedforward signals to mitigate noise and reduce the performance requirements of the error loop filter, allowing for smaller and lower power implementations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high-performance components are used to handle high-frequency noise and residual modulation tones, then noise handling capability is improved, but circuit size and power consumption increase

Engineering Contradiction:

Improvenoise handling capabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent extracts and removes the harmful high-frequency noise and residual modulation tones from the feedback signal using a low-pass filter before processing. This eliminates the need for high-performance components to handle these noise components, thereby reducing power consumption while maintaining noise handling capability for actual signal errors.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The feedback signal processing is segmented into two distinct paths: one path filters out high-frequency noise components using a low-pass filter, while another path preserves the original feedback signal for error calculation. This segmentation allows the system to handle noise separately from legitimate error signals, reducing the performance requirements of subsequent processing components.

Inventive Principle:

Principle #1Segmentation

2Reliability

If high-performance components are used to handle high-frequency noise and residual modulation tones, then noise handling capability is improved, but circuit size increases

Engineering Contradiction:

Improvenoise handling capabilityVSAvoidcircuit size

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent extracts and removes the harmful high-frequency noise and residual modulation tones from the feedback signal using a low-pass filter before processing. This eliminates the need for high-performance components to handle these noise components, thereby reducing circuit size while maintaining noise handling capability for actual signal errors.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #1Segmentation

3Measurement precision

If precise matching of feedback and feedforward signals is implemented, then error detection accuracy is improved, but device complexity increases

Engineering Contradiction:

Improveerror detection accuracyVSAvoiddevice complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent introduces a low-pass filter as an intermediary component that processes the feedback signal before it is used for error detection. This intermediary filters out high-frequency noise and residual modulation tones, allowing for simpler matching between feedback and feedforward signals while maintaining accurate error detection for legitimate signal errors.

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution reduces circuit size and power consumption while maintaining performance by effectively handling high-frequency noise and improving loop gain, thus enhancing the efficiency and stability of Class-D amplifiers.

Implementation Method 1

a first low-pass filter configured to apply low pass filtering to said feedforward signal to provide a filtered feedforward signal

Methodology Applied

Scientific EffectLow-pass filtering: Filter (electronic)

Implementation Method 2

a second low-pass filter configured to receive and low-pass filter the first feedback signal to provide the filtered feedback signal

Methodology Applied

Scientific EffectLow-pass filtering: Filter (electronic)

Implementation Method 3

The error path comprises an error loop filter with an analog input filter stage

Methodology Applied

Scientific EffectAnalog filtering: Filter (electronic)

Data Source

PatentUS20250337374A1Modular circuits

Publication Date: 2025.10.30 CIRRUS LOGIC INT SEMICON LTD

AI summary

This application relates to methods and apparatus for modulator circuits, for outputting a modulated signal for driving a switching output stage. A first digital modulator generates the modulated signal based on an input signal modified by a correction signal. A second digital modulator generates a feedforward signal from the input signal, which is filtered by a first low-pass filter to provide a filtered feedforward signal. The correction signal is generated by an error path that processes an error signal which is generated as a difference between the filtered feedforward signal and a filtered feedback signal. The filtered feedback signal corresponds to a received feedback signal, indicative of an output from the switching output stage, with low-pass filtering applied. The error path has a loop filter with an analog input stage and the received feedback signal is applied to the error path downstream of the analog input stage for phase lead compensation.