Amplifier Output Stage Coupling for Click and Pop Noise Reduction
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Solution Overview
Problem
Audio amplifiers face challenges in reducing click and pop noise during startup and shutdown, particularly due to glitches and voltage offsets, which are difficult to mitigate with existing technologies, especially for high-quality audio applications where noise levels below 100 microvolts are required.
Innovation Solution
An amplifier circuit with a main and secondary output stage, controlled by a waveform generator that adjusts resistive coupling between the stages during power-up and power-down to minimize noise, using a signal coupler to manage the coupling resistance and enable/disable stages to reduce noise at the output terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional amplifier startup and shutdown circuits are used, then the amplifier can be powered on and off, but click and pop noise is generated at the output terminal
Solution Approach 1:
The amplifier output stage is divided into a main output stage and a secondary output stage. The secondary stage is specifically designed to handle startup and shutdown operations, while the main stage handles normal audio amplification. This segmentation allows noise reduction during power transitions without affecting normal operation.
Solution Approach 2:
A waveform generator is introduced as an intermediary component that produces controlled waveforms to gradually couple or decouple the secondary output stage from the main output stage during startup and shutdown. This intermediary control mechanism prevents abrupt transitions that cause click and pop noise.
2Speed
If the secondary output stage is immediately coupled to the main output stage during startup, then signal amplification begins quickly, but voltage offsets and glitches cause noise
Solution Approach 1:
During startup, the secondary output stage is activated first and gradually coupled to the main output stage before full signal amplification begins. The waveform generator produces a controlled ramp waveform that slowly increases the coupling, allowing voltage offsets to settle before they affect the main output, thus preventing noise while maintaining reasonable startup speed.
3Manufacturing precision
If the amplifier uses high gain amplification, then signal quality is improved, but noise from the circuit is also amplified
Solution Approach 1:
The harmful noise generation process is extracted and isolated into the secondary output stage, which operates separately from the main high-gain amplification path. The secondary stage handles the noisy startup and shutdown operations, while the main stage maintains high gain for clean signal amplification. This extraction prevents circuit noise from being amplified along with the signal.
Data Source
AI summary
An amplifier with improved noise reduction is disclosed. In one implementation, an amplifier is provided that includes a main output stage configured to output an amplified signal at a main output terminal, a secondary output stage configured to output a copy of the amplified signal at a secondary output terminal, and a signal coupler configured to provide a variable resistance coupling between the secondary output terminal and the main output terminal to reduce noise at the main output terminal.