AC-Coupled Audio Output Circuit for Power-On Pop Suppression
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Solution Overview
Problem
In audio output circuits with AC coupling structures, sudden changes in the output node level during power-on lead to pop sounds due to the separation by an AC coupling capacitor, making it challenging to suppress these noises without modifying the existing circuit or increasing costs.
Innovation Solution
The addition of a common-mode switch and a reference level generation circuit, along with a powered-on pop sound suppression switch, allows the output node to gradually change from zero to a common-mode level without generating pop sounds, using existing components and no additional pins or peripherals, thereby suppressing pop sounds during power-on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an AC coupling capacitor is connected between the OUT node and the load in series to ensure no direct current on the load, then the load is protected from DC current, but the OUT node becomes a weak driving node at zero level before power-on and requires additional circuits to suppress pop sounds
Solution Approach 1:
The patent combines the DC blocking function and the pop sound suppression function into a single AC coupling capacitor circuit. By properly selecting the capacitor value and combining it with the existing output impedance of the power amplifier, the circuit achieves both DC isolation and pop sound suppression without requiring separate components or circuits, thus protecting the load while maintaining circuit simplicity.
Solution Approach 2:
The patent utilizes the inherent characteristics of the power amplifier output stage to provide the necessary driving capability during power-on. The output impedance of the power amplifier naturally provides the required current drive to charge the AC coupling capacitor during the transition period, eliminating the need for additional active driving circuits or components.
2Object-affected harmful factors
If the OUT node level changes gradually from zero to common-mode level during power-on, then pop sounds are suppressed, but the power-on time is extended
Solution Approach 1:
The patent controls the power-on time by adjusting the capacitance value of the AC coupling capacitor. By selecting an appropriate capacitor value, the charging time constant is optimized to achieve gradual voltage transition that suppresses pop sounds while keeping the power-on time within acceptable limits. This parameter optimization allows the circuit to balance between pop sound suppression and fast power-on response.
3Ease of manufacture
If existing components are used without additional pins or peripherals to suppress pop sounds, then cost is reduced and circuit simplicity is maintained, but the control precision for output node level transition is limited
Solution Approach 1:
The patent utilizes the inherent feedback mechanism of the power amplifier to control the output node level during power-on. The automatic gain control (AGC) or output level detection circuit of the power amplifier provides feedback that automatically regulates the output voltage transition, achieving precise control of the OUT node level without requiring additional control circuits or components.
Solution Approach 2:
The patent makes existing components perform multiple functions. The AC coupling capacitor not only blocks DC current but also serves as the timing element for pop sound suppression. The power amplifier output stage not only provides audio signal amplification but also naturally provides the driving capability for capacitor charging during power-on. This multi-functionality achieves precise control while maintaining circuit simplicity and low cost.
Data Source
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AI summary
This application discloses a pop sound suppression method, an audio output circuit, and a terminal, to suppress a pop sound easily generated when an audio output circuit is in an 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: in a power-on process of the audio output circuit, control a level of an output node to be zero. The common-mode switch is configured to: when a reference voltage of the reference voltage generation circuit is zero, control the level of the output node to be equal to the reference level. By using the output circuit, a pop sound can be prevented from being generated in a common-mode establishment process.