AC-Coupled Audio Output Circuit With Staged Common-Mode Startup
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Solution Overview
Problem
In audio output circuits using AC coupling structures, sudden changes in the output node level during power-on lead to the generation of 'pop' sounds, which are unpleasant for humans due to their sensitivity to signal changes.
Innovation Solution
The implementation of a pop sound suppression method involving an audio output circuit with a powered-on pop sound suppression switch, a common-mode level buffer, and a reference level generation circuit, where the output node is initially pulled down to zero and then gradually brought to the common-mode level using a common-mode switch, preventing sudden level changes that cause 'pop' sounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the output node level is suddenly changed from zero to common-mode level during power-on, then the power-on process is completed quickly, but pop sounds are generated due to sudden signal change
Solution Approach 1:
The patent applies preliminary action by pre-charging the output node to the common-mode level through a dedicated power-on pop sound suppression switch before the audio signal is output. This preliminary charging action ensures that when the audio signal starts, there is no sudden level change from zero to common-mode level, thereby preventing pop sounds while maintaining fast power-on.
2Object-affected harmful factors
If the output node level is gradually changed from zero to common-mode level, then pop sounds are suppressed, but the power-on process takes longer time
Solution Approach 1:
The patent uses a power-on pop sound suppression switch that is enabled only during the power-on period to pre-charge the output node to the common-mode level. This preliminary action is completed quickly through a dedicated charging path, and then the switch is disabled, allowing the system to transition to normal operation without extending the overall power-on time.
3Object-affected harmful factors
If a pop sound suppression circuit is added to the audio output circuit, then pop sounds are suppressed, but the circuit complexity increases
Solution Approach 1:
The patent introduces a common-mode level buffer as an intermediary component between the power-on pop sound suppression switch and the output node. This buffer efficiently transfers the common-mode level to the output node during power-on, achieving effective pop sound suppression while keeping the additional circuit components minimal and the overall circuit structure simple.
4Object-affected harmful factors
If the output node is pulled down to zero level using a suppression circuit, then pop sounds are suppressed, but the output node driving capability is weakened
Solution Approach 1:
The patent implements a dynamic switching mechanism where the power-on pop sound suppression switch is enabled only during the power-on period and disabled during normal operation. During power-on, the switch pulls the output node to zero level to prevent pop sounds, but during normal operation, the switch is disabled and the common-mode level buffer provides strong driving capability for the audio signal output.
Data Source
AI summary
A pop sound suppression method, an audio output circuit, and a terminal suppress a pop sound that is generated when an audio output circuit is in an alternating current (AC) coupling structure. The output circuit includes an output power amplifier, a common-mode voltage buffer, a reference voltage generation circuit, a powered-on pop sound suppression switch, and a common-mode switch. The powered-on pop sound suppression switch is configured to control, in a power-on process of the audio output circuit, a voltage level of an output node to be zero. The common-mode switch is configured to control, when a reference voltage level of the reference voltage generation circuit is zero, the voltage level of the output node to be equal to the reference level.