Duplicate Feedback Circuit for Pop-Free Class D Amplifier Switching
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Solution Overview
Problem
Class D amplifiers experience unwanted pop and click noise during power-on and power-off due to the establishment of quiescent voltages, which existing technologies have not fully addressed, particularly in maintaining the operating point of the feedback loop without causing step changes that lead to audio artifacts.
Innovation Solution
A duplicate feedback resistor network and input switches are used to drive a control circuit, which in turn controls output pre-drivers and an H-bridge switch, establishing a differential feedback loop to suppress noise by managing offsets and duty cycles during power transitions, ensuring the circuit operates differentially around a common mode bias point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a feedback loop is established in Class D amplifiers to compensate for variations in bus voltages and correct distortion, then the amplifier performance is improved, but pop and click noise occurs during power-on and power-off due to step changes in the output
Solution Approach 1:
The patent applies preliminary action by establishing the operating point of the feedback loop before power transitions occur. The circuit proactively sets up the feedback network in advance to prevent step changes in the output, thereby eliminating pop and click noise during power-on and power-off sequences
Solution Approach 2:
The patent introduces an intermediary feedback network that acts as a mediator between the power supply and the output stage. This intermediate feedback path smooths out voltage transitions and prevents direct coupling of power supply steps to the output, thereby suppressing audible artifacts
2Ease of operation
If quiescent voltages are established during power-on to set the operating point, then the amplifier is ready for operation, but unwanted audio artifacts are generated on the speaker output
Solution Approach 1:
The patent uses feedback by continuously monitoring the output voltage and adjusting the operating point accordingly. The feedback network ensures that quiescent voltages are established in a controlled manner that does not produce audible steps, maintaining both operational readiness and audio cleanliness
Data Source
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AI summary
A circuit and a method are provided for suppressing the pop and click noise during the power on and power off of Class D amplifiers. The technique also suppresses pops and clicks when the Class D amplifier enters or exits standby mode. A duplicate feedback network is used to establish the stable operating points, including offsets in the Class D circuit without turning on the outputs. The technique works by gradually propagating or dissipating the offset through the signal path of a Class D amplifier by swapping the differential outputs using switches to suppress pops and clicks when starting up and shutting down the amplifier.