Amplifier Output Stage Control for Pop and Click Noise
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Solution Overview
Problem
Existing audio amplifiers suffer from turn-on and turn-off transients that produce noise, known as pop or click noises, degrading their usability.
Innovation Solution
The amplifier circuit employs a multi-stage configuration with a bypass buffer, clock control circuit, and operating states to minimize noise by disabling output stages during startup and charging, using feedback resistors and capacitors to stabilize voltages and prevent noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the amplifier output stage is enabled during startup and shutdown, then the amplifier can immediately process audio signals, but turn-on and turn-off transients produce pop and click noises
Solution Approach 1:
The amplifier circuit performs preliminary charging of the output coupling capacitor through a dedicated charging circuit before enabling the output stage. This preliminary action ensures the capacitor is charged to the appropriate voltage level before audio signals are passed, preventing turn-on transients and pop noises while maintaining quick response capability.
Solution Approach 2:
The amplifier circuit is divided into separate functional stages: a charging circuit that charges the output coupling capacitor, and an output stage that processes audio signals. The charging circuit operates independently during startup and shutdown, while the output stage remains disabled during these transitions. This segmentation allows each stage to perform its function without causing transients, resolving the contradiction between quick response and noise prevention.
2Object-generated harmful factors
If the output stage is disabled during charging, then turn-on transients are reduced, but the amplifier cannot immediately process audio signals
Solution Approach 1:
The charging circuit performs the capacitor charging action in advance before the output stage is enabled. By pre-charging the output coupling capacitor to the appropriate voltage level during startup, the circuit eliminates the need for delay after enabling the output stage, thus reducing startup time while preventing transients.
Solution Approach 2:
The charging circuit operates continuously during startup and shutdown phases, maintaining the capacitor at the appropriate voltage level. This continuous charging action ensures that when the output stage is enabled, the capacitor is already charged and ready to pass audio signals immediately, eliminating both transients and startup delay.
3Object-generated harmful factors
If feedback resistors and capacitors are used to stabilize voltages, then noise is reduced, but circuit complexity increases
Solution Approach 1:
The feedback network is segmented into specific resistors and capacitors placed at strategic locations in the amplifier circuit. Rather than using a complex overall feedback mechanism, discrete feedback components are used to stabilize voltages at critical nodes, reducing noise while maintaining relatively simple circuit architecture.
Solution Approach 2:
Feedback resistors and capacitors are incorporated into the amplifier circuit to stabilize voltages and reduce noise. The feedback network monitors output voltages and adjusts internal node voltages accordingly, suppressing noise without requiring complex circuit modifications.
Data Source
AI summary
In one embodiment, an amplifier circuit is formed to minimize pop and click noise on the outputs of the amplifier circuit. The amplifier circuit is configured to place an output stage of the amplifier circuit in a high impedance state to minimize the pop and click noise. In another embodiment, the amplifier circuit is configured to couple the inputs of two amplifiers together to minimize the pop and click noise.