Audio Amplifier Common-Mode Bandwidth Control
Solution Overview
Problem
Audio amplifiers in personal devices suffer from distortion due to slow tracking of power supply voltage transitions by common-mode voltage generators and feedback loops, leading to clipping during mode changes, which affects power efficiency and battery life.
Innovation Solution
An audio amplifier circuit with a power amplifier, power supply, common-mode voltage generator, and control circuit that adjusts bandwidths during power supply transitions to ensure the common-mode voltage generator and feedback loop respond effectively, preventing distortion by increasing their bandwidths to match the power supply's transition speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the power supply voltage transitions quickly between magnitudes to improve power efficiency, then power efficiency is improved, but distortion increases because the common-mode voltage generator and feedback loop cannot track the transitions fast enough
Solution Approach 1:
The patent applies dynamics by making the bandwidth of the common-mode voltage generator and feedback loop adjustable rather than fixed. During power supply voltage transitions, the bandwidth is dynamically increased to enable faster tracking, while during normal operation it returns to standard levels for power efficiency. This dynamic adjustment resolves the contradiction between fast tracking (reliability) and power efficiency.
Solution Approach 2:
The patent changes the bandwidth parameter of the common-mode voltage generator and feedback loop based on operating conditions. When a power supply voltage transition is detected, the bandwidth parameter is increased to allow faster response. This parameter change enables the system to track quick voltage transitions without distortion while maintaining power efficiency during steady-state operation.
2Loss of energy
If the common-mode voltage generator and feedback loop are optimized for high power supply rejection ratio and low power consumption, then power efficiency is improved, but the tracking speed of power supply voltage transitions decreases
Solution Approach 1:
The system dynamically adjusts the bandwidth (tracking speed) of the common-mode voltage generator and feedback loop based on whether a power supply voltage transition is occurring. During transitions, bandwidth is increased for fast tracking; during normal operation, bandwidth is reduced for low power consumption. This dynamic behavior resolves the contradiction between tracking speed and power consumption.
Solution Approach 2:
The control circuit detects power supply voltage transitions in advance and proactively increases the bandwidth of the common-mode voltage generator and feedback loop before the transition completes. This preliminary action ensures the circuit is ready to track the voltage change quickly, preventing distortion while minimizing the duration of high power consumption state.
Data Source
AI summary
A control circuit coupled to a differential audio output stage may, responsive to a transition in a power supply voltage generated by a power supply, modify at least one of: (i) a first bandwidth associated with the power supply; (ii) a second bandwidth associated with a common-mode voltage generator for generating a desired output common-mode voltage based on the power supply voltage; and (iii) a third bandwidth associated with a common-mode feedback loop of the audio-output stage for setting an actual common-mode voltage at each of the pair of differential output terminals based on the desired output common-mode voltage; such that the second bandwidth is greater than or substantially equal to the first bandwidth during the transition and the third bandwidth is greater than or substantially equal to the second bandwidth during the transition.