Audio Amplifier Feedback Circuit for Silent Power Transitions
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Solution Overview
Problem
Audio amplifiers, particularly class D amplifiers, generate audible noise due to charging and dissipating power from capacitors and inductors during activation and deactivation, causing unpleasant disturbances.
Innovation Solution
Incorporating a feedback path with a switch that maintains a closed loop when transistors are deactivated, allowing charge dissipation without noise, and extending the enable signal period during voltage changes to prevent disturbances, along with a control circuit using operational amplifiers and integrating capacitors to manage PWM signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the power output stage is deactivated immediately when supply voltage ceases, then the response time is reduced, but audible noise is generated due to charge dissipation from capacitors and inductors
Solution Approach 1:
The patent applies preliminary action by keeping the power output stage active for a predetermined time period after the supply voltage ceases. This ensures that the capacitors and inductors have sufficient time to dissipate their stored charge gradually, preventing audible noise while maintaining a relatively quick response compared to traditional methods that wait for complete power dissipation.
2Stability of the object's composition
If the feedback path is maintained during power transitions, then the stability is improved, but the complexity of the circuit increases
Solution Approach 1:
The patent implements feedback by maintaining the feedback path active during power transitions. The feedback signal from the output is continuously monitored and used to adjust the operation of the power output stage, ensuring stable behavior during startup and shutdown. This prevents oscillations and audible disturbances while maintaining circuit stability without requiring additional complex control mechanisms.
3Measurement precision
If the integrating capacitor is allowed to charge during power-up, then the PWM signal accuracy is improved, but audible disturbances occur during power transitions
Solution Approach 1:
The patent applies preliminary action by pre-charging the integrating capacitor to a predetermined voltage level before the power output stage becomes active. This ensures that the capacitor is ready to accurately integrate the PWM signal from the start, improving signal accuracy. By preparing the capacitor in advance and controlling its charging sequence, the patent prevents audible disturbances that would otherwise occur during the power transition when the capacitor charges abruptly.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Significantly reduces or eliminates audible disturbances during power-up and power-down cycles, improving the stability and noise performance of audio amplifiers.
Implementation Method 1
a low pass filter configured to filter a carrier signal from the amplified pulse width modulation signal
Implementation Method 2
a feedback path including an impedance connected between the pulse width modulation circuit and a control circuit of the audio amplifier
Implementation Method 3
The control circuit may comprise an integrating capacitor. Further, the feedback path may be further configured to establish a first state of the integrating capacitor when the power output stage is inactive and a second state of the integrating capacitor when the power output stage is active
Data Source
AI summary
Aspects disclosed herein eliminate audible disturbances that may occur when an audio amplifier is activated and deactivated. A feedback circuit is used to maintain a closed loop when transistors of a power output stage are activate or deactivated, thereby enabling the charge to build or dissipate without causing an audible disturbance. Further, in certain implementations, the power output stage may remain in an enable state for a period of time after deactivation of the audio amplifier regardless of whether an audio input signal is received enabling dissipation of charge without causing an audible disturbance.