Audio Amplifier Zero-Crossing Control Near Power Supply Rails
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Solution Overview
Problem
Class-D audio amplifiers and haptic drivers with differential H-bridge output stages face challenges in maintaining low-distortion operation near power supply rails due to rising effective output impedance, leading to reduced signal swing and efficiency at low amplitudes.
Innovation Solution
The implementation of multiple driver circuits and a control circuit that selects between single-ended and differential operating states, using pulse-state suppression logic to manage zero-crossings and shift the quiescent operating point, allowing for low-distortion operation near power supply rails by controlling the common-mode voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the output voltage nears one of the power supply rails in a differential H-bridge output stage, then the amplifier can operate with higher efficiency and greater signal swing, but the effective output impedance of the switching devices rises rapidly causing distortion at low amplitudes
Solution Approach 1:
The patent implements dynamic switching between single-ended and differential operating modes based on the instantaneous signal amplitude and polarity. The control circuit monitors the input signal and selectively activates either single-ended drivers (for low amplitude signals near zero-crossings) or differential H-bridge drivers (for high amplitude signals), thereby adapting the output impedance characteristics to the current operating conditions and preventing distortion while maintaining efficiency.
Solution Approach 2:
The patent changes the operating parameters of the amplifier by shifting the common-mode voltage and switching between different driver configurations. By dynamically adjusting which drivers are active (single-ended vs. differential) based on the signal characteristics, the system optimizes the trade-off between output swing/efficiency and linearity, allowing operation near power supply rails without excessive distortion.
2Manufacturing precision
If the common-mode voltage is set between the power supply rails to avoid distortion, then low-amplitude operation is improved, but the potential signal swing and efficiency are reduced
Solution Approach 1:
The patent dynamically adjusts the common-mode voltage and driver configuration based on the instantaneous signal amplitude. For low-amplitude signals, the system uses single-ended drivers with appropriate common-mode voltage settings to maintain linearity. For high-amplitude signals, it switches to differential H-bridge operation that allows the common-mode voltage to approach the power supply rails, maximizing signal swing and efficiency without compromising low-amplitude performance.
3Manufacturing precision
If single-ended driver circuits are used for low-amplitude signals, then zero-crossing distortion is reduced, but the overall amplifier complexity increases due to multiple driver circuits and control logic
Solution Approach 1:
The patent segments the amplifier into multiple independent driver circuits (single-ended drivers and differential H-bridge drivers) that can be selectively activated. Each driver type is optimized for specific operating conditions, and the control circuit intelligently selects which drivers to activate based on the input signal characteristics. This segmentation allows the system to use the simplest appropriate driver configuration for each signal condition, managing complexity through functional decomposition.
Solution Approach 2:
The patent implements a universal amplifier architecture that can operate in multiple modes (single-ended and differential) using a shared set of power supply rails and output stages. The control circuit provides multi-functionality by selecting between different driver configurations without requiring completely separate amplifier circuits, thereby managing complexity while maintaining the ability to optimize performance for different signal conditions.
Data Source
AI summary
Amplifier circuits provide operation with low-distortion zero crossings outside of a unipolar power supply voltage range. The amplifiers include multiple driver circuits and a control circuit. The control circuit selects between actively operating selected ones of the multiple driver circuits or all of the multiple driver circuits, according to an input signal to be reproduced by one or more of the multiple amplifier driver circuits. The control circuit determines a splice point at which the control circuit selects between actively operating selected ones of the multiple driver circuits or all of the multiple driver circuits.