Class D Audio Amplifier Feedback for Common-Mode Voltage Stability
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Solution Overview
Problem
Class D audio amplifiers experience performance deterioration due to fluctuations in common mode voltage, which can occur under various power supply conditions, affecting the overall amplification efficiency and signal quality.
Innovation Solution
An audio amplifier design that includes a common mode compensation circuit, which generates and applies compensation voltages to the loop filter based on the state of the output signal pair, stabilizing the common mode voltage and maintaining it at a constant level, thereby addressing the fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a class D amplifier operates by fully turning on or off a MOS switch through PWM control, then amplification efficiency is improved with almost no power loss, but common mode voltage fluctuation occurs under various power supply conditions affecting signal quality
Solution Approach 1:
The patent implements a feedback mechanism where the common mode voltage is sensed from the differential output signals, compared against a reference voltage, and the resulting error signal is used to adjust the PWM duty cycle. This closed-loop feedback system dynamically compensates for common mode voltage fluctuations while maintaining the high-efficiency switching operation of the class D amplifier.
Solution Approach 2:
The patent dynamically changes the PWM duty cycle parameter in response to detected common mode voltage fluctuations. By adjusting the duty cycle of the PWM signal driving the MOS switch, the system compensates for common mode voltage variations and maintains stable output signal quality without sacrificing amplification efficiency.
2Use of energy by moving object
If PWM control is used to achieve high-efficiency amplification, then power consumption is reduced, but common mode voltage fluctuation deteriorates amplification performance
Solution Approach 1:
The system employs feedback control where the common mode voltage is continuously monitored and the PWM duty cycle is adjusted accordingly. This allows the amplifier to maintain high efficiency while compensating for performance-deteriorating common mode fluctuations through dynamic parameter adjustment.
Solution Approach 2:
The patent introduces dynamic adjustment of the PWM duty cycle based on real-time common mode voltage conditions. This dynamic control approach enables the system to adapt to varying power supply conditions and maintain optimal amplification performance while preserving the energy efficiency benefits of PWM operation.
3Productivity
If the driver generates output signal pair based on PWM signals, then amplification efficiency is maintained, but fluctuation in common mode voltage of output signal affects loop filter performance
Solution Approach 1:
The patent extracts the common mode voltage component from the differential output signals and feeds it back through a control loop that adjusts the PWM duty cycle. This feedback mechanism compensates for common mode fluctuations before they adversely affect the loop filter, thereby maintaining both amplification efficiency and loop filter performance.
Solution Approach 2:
The system takes preliminary anti-action by detecting and compensating for common mode voltage fluctuations at an early stage in the signal path. By adjusting the PWM duty cycle in response to detected common mode variations, the system prevents these fluctuations from propagating to and degrading the loop filter performance.
Data Source
AI summary
An audio amplifier includes a loop filter configured to receive a differential input signal pair, a pulse-width modulation (PWM) signal generator configured to generate PWM signals, corresponding to the differential input signal pair, based on signals received from the loop filter, a driver configured to generate an output signal pair based on the PWM signals, a feedback circuit configured to feed back the output signal pair to the loop filter, and a common mode compensation circuit configured to compensate for a fluctuation in a common mode voltage of the fed-back output signal pair. The common mode compensation circuit generates a compensation voltage for each of a plurality of levels of the common mode voltage, and provides the generated compensation voltage to the loop filter.