Common-Mode Loop State Hold for Smooth Multi-Mode Amplifier Switching

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Solution Overview

Problem

Controlling the output common mode during transitions between modes in multi-mode amplifiers is challenging, leading to signal overshoot and undershoot, particularly in PWM mode due to saturation of the common-mode integrator loop.

Innovation Solution

Implementing an auxiliary circuit that maintains the state of the common-mode feedback loop during transitions between modes, either through feedforward or feedback control, to preserve the charge on the integrating capacitor and prevent saturation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the amplifier switches between PWM mode and linear mode to achieve better efficiency and lower output noise, then the amplifier can generate desired behavior in different operating conditions, but signal overshoot and undershoot occur during mode transitions due to saturation of the common-mode integrator loop

Engineering Contradiction:

Improvemulti-mode operation capabilityVSAvoidsignal stability during mode transition

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The auxiliary circuit maintains the state of the common-mode feedback loop during PWM mode operation, preparing it for smooth transition to linear mode. By preserving the integrator capacitor charge and preventing saturation during the PWM phase, the system is pre-conditioned for stable operation when switching to linear mode, eliminating overshoot and undershoot artifacts.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If a common-mode feedback loop is used to control output common mode during mode switching, then switching artifacts are minimized, but the feedback loop saturates during PWM mode operation causing transition instability

Engineering Contradiction:

Improvecontrol accuracy during mode switchingVSAvoidcommon-mode loop state stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The system separates the common-mode control function into two distinct circuits: the main common-mode feedback loop that operates during linear mode, and an auxiliary circuit that maintains the feedback loop state during PWM mode. This segmentation allows each circuit to be optimized for its specific operating phase without interfering with the other, preventing saturation while maintaining control accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The auxiliary circuit acts as an intermediary between the PWM mode operation and the common-mode feedback loop. It preserves the state of the feedback loop during PWM operation by maintaining the integrator capacitor charge, thereby mediating the transition between modes and preventing direct conflict that would cause saturation and instability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12512790B2Output common-mode control loop for fast and smooth transition in multi-mode amplifiers

Publication Date: 2025.12.30 CIRRUS LOGIC INC

AI summary

A system may include a pulse-width modulation mode path configured to drive a load at an output of the system in a first mode of operation, a linear mode path configured to drive the load in a second mode of operation, a common mode control feedback loop configured to set a value of a common mode output signal at the output in the second mode of operation, and an auxiliary circuit coupled to the common mode feedback control loop and configured to maintain a state of the common mode feedback control loop during the first mode of operation as the state was or will be during the second mode of operation.