Audio Output Stage Switching Between Open-Loop and Closed-Loop Modes
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Solution Overview
Problem
Class-D power amplifiers in audio processing circuits require a large analog-to-digital converter (ADC) for feedback, limiting the reduction of chip area and performance improvement due to their closed-loop structure, especially when digital modulation circuits are implemented, which hinders the benefits of advanced semiconductor processes.
Innovation Solution
An audio processing circuit with a digital signal processing circuit, digital modulation circuit, output stage, voltage regulator, and signal detection circuit that dynamically switches between open-loop and closed-loop structures based on signal strength, using a voltage regulator to reduce noise in small signal modes and direct supply voltage in large signal modes, allowing for a smaller chip area while maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a closed-loop structure with ADC is used in class-D power amplifier, then performance indicators (THD+N, PSRR) are improved, but chip area increases and benefits of advanced semiconductor processes are lost
Solution Approach 1:
The patent implements a dynamic switching mechanism that changes the feedback structure based on signal strength. For large signals, the closed-loop structure with ADC is activated to improve performance indicators. For small signals, the system switches to an open-loop or simplified feedback mode to reduce chip area. This dynamic adaptation allows the system to optimize between performance and area requirements under different operating conditions.
2Area of stationary object
If digital modulation circuit is implemented, then chip area is reduced and semiconductor process benefits are achieved, but closed-loop feedback performance is compromised
Solution Approach 1:
The patent applies different feedback strategies based on local signal conditions. Instead of using a uniform closed-loop structure throughout, the system implements signal-strength-dependent feedback where the feedback path is selectively activated or deactivated. This allows digital modulation circuits to be used in small-signal regions while maintaining analog feedback paths only when necessary for large-signal performance, thereby achieving area reduction without completely sacrificing feedback benefits.
3Reliability
If a large area ADC is designed to maintain class-D power amplifier performance, then performance indicators are improved, but chip area reduction is prevented
Solution Approach 1:
The patent implements partial feedback action by selectively enabling the ADC and feedback path only when signal strength exceeds a certain threshold. Instead of continuously operating a large-area ADC at full capacity, the system uses the ADC partially - only during large-signal conditions where feedback is most beneficial. This partial action approach maintains amplifier performance when needed while allowing the use of smaller ADCs and reducing overall chip area compared to continuous full-capacity feedback operation.
Data Source
AI summary
The present invention discloses an audio processing circuit, wherein when the audio processing circuit determines that a signal being processed is a small signal, an output stage uses a regulated supply voltage provided by a voltage regulator, and the output stage uses an open-loop structure to reduce noise of an output audio signal; and when the audio processing circuit determines that the signal being processed is a large signal, the output stage directly uses the supply voltage without using the regulated supply voltage, and the output stage uses a closed-loop structure to reduce the total harmonic distortion of the output audio signal. By using the present invention, the audio processing circuit can have a good performance indicator with a small chip area design.