Cascade Audio Amplifier Startup with Pull-Down POP Noise Control
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Solution Overview
Problem
Audio circuits generate POP noise during operational amplifier path establishment due to offset voltages, causing discomfort to human ears due to sudden voltage changes.
Innovation Solution
An audio processing circuit with a cascade operational amplifier circuit and a pull-down circuit, where the second operational amplifier gradually changes its output resistance from high to low, controlling the voltage at the output node to increase slowly, and a ramp signal controller manages the variable resistor to prevent sudden voltage changes, effectively suppressing POP noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the operational amplifier path establishment procedure is performed quickly, then the establishment speed is improved, but sudden voltage changes occur causing POP noise
Solution Approach 1:
The pull-down circuit is activated before the operational amplifier path establishment to pre-establish a reference voltage level at the output node. This preliminary action ensures that when the operational amplifier path is established, there is no sudden voltage change, thereby preventing POP noise while maintaining fast establishment speed.
Solution Approach 2:
The pull-down circuit acts as an intermediary between the operational amplifier path and the output node. It mediates the voltage transition by providing a controlled discharge path that prevents abrupt voltage changes, thus eliminating POP noise without slowing down the overall establishment process.
2Measurement precision
If the output resistance of the second operational amplifier is reduced, then the voltage control precision is improved, but the voltage changes too quickly causing POP noise
Solution Approach 1:
The output resistance of the second operational amplifier is made dynamic rather than fixed. During the path establishment phase, the output resistance is increased to slow down voltage changes and prevent POP noise. Once the path is established, the output resistance returns to its normal low value for precise voltage control. This dynamic adjustment resolves the contradiction between control precision and POP noise prevention.
Data Source
AI summary
An audio processing circuit includes a cascade operational amplifier circuit, an output node, and a pull-down circuit. The cascade operational amplifier circuit includes a first operational amplifier circuit and a second operational amplifier circuit. The first operational amplifier circuit includes a main operational amplifier and a secondary operational amplifier that are connected in parallel. The pull-down circuit is configured to pull down a voltage at the output node after the first operational amplifier circuit is turned on. The second operational amplifier circuit is configured to, after the secondary operational amplifier is turned on, control a voltage gain of the secondary operational amplifier to change gradually from low to high.