Audio Amplifier Power-Up Control for Pop-Noise Prevention
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Solution Overview
Problem
Existing audio power management systems experience annoying clicks and pops during power cycling due to sudden voltage changes, which are difficult to eliminate without complicating the circuit or requiring specialized amplifiers.
Innovation Solution
A voltage rising control circuit slowly increases the supply voltage of the audio amplifier during power-up, using a low resistive switch and a control circuit to prevent sharp voltage edges from reaching the speaker, thereby avoiding transient noises.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low gain amplifier is used to charge the DC blocking capacitor with increased rising time, then pop noise is reduced, but the circuit becomes more complicated and requires multiple operational amplifiers
Solution Approach 1:
The patent divides the power-up sequence into distinct phases: a first power-up phase where the DC blocking capacitor is charged through a high-value resistor (preventing pop noise), and a second power-up phase where the main amplifier is enabled. This temporal segmentation allows the same amplifier to serve different functions at different times, avoiding the need for multiple amplifiers while still preventing pop noise.
Solution Approach 2:
The patent performs preliminary charging of the DC blocking capacitor before the main amplifier operation begins. By pre-charging the capacitor through the high-value resistor during an initial power-up phase, the system prepares the capacitor in a state that prevents pop noise during subsequent amplifier operation, without requiring continuous complex circuitry.
2Object-affected harmful factors
If a symmetric output audio amplifier is used to eliminate DC value influence, then pop noise is prevented, but the amplifier becomes more difficult to implement compared to Class-AB single supply amplifiers
Solution Approach 1:
The patent dynamically controls the enable signal to the amplifier, creating different operational phases. During the first power-up phase, the amplifier is disabled while the DC blocking capacitor charges. During the second phase, the amplifier is enabled only after the capacitor is sufficiently charged. This dynamic control allows a simple Class-AB single supply amplifier to behave as if it were protected from pop noise conditions without requiring complex symmetric output circuitry.
Solution Approach 2:
The patent changes the operational parameters of the amplifier by controlling the enable signal timing. By adjusting when the amplifier is enabled relative to the power-up sequence, the system achieves pop noise prevention through parameter control rather than through complex circuit architecture. The same amplifier can operate in different modes depending on the timing of the enable signal.
3Speed
If power is applied suddenly to the audio system, then power-up is fast, but clicks and pops are generated due to voltage changes outside recommended operating range
Solution Approach 1:
The patent implements a two-stage power-up sequence with periodic phases: first, the DC blocking capacitor is charged during an initial phase; second, the main amplifier is enabled in a subsequent phase. This periodic, multi-phase approach allows the system to balance speed and noise prevention by structuring the power-up as distinct temporal stages rather than a single simultaneous event.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively prevents pop noise without needing symmetric output amplifiers or multiple operational amplifiers, simplifying the circuit and reducing noise during power-up, while maintaining efficient audio output.
Implementation Method 1
A voltage rising control circuit slowly increases the supply voltage of the audio amplifier during power-up
Implementation Method 2
The click-on noise that would appear without the additional circuit is depicted in Figure.2. The solution is to slow down the amplifier's supply voltage rising time with a voltage rising control circuit
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
An apparatus and method is disclosed to control an output from an amplifier used in an audio power management system during a powering sequence. This invention solves the problem of pop-noise (also known as click-on noise) which occurs at the power-up interval when single supply-asymmetric output audio amplifier is used. Pop-noise is quite annoying and easily audible at class AB audio amplifiers. Main reason for this problem is the supply voltage rising time when the audio amplifier switched on. This time is increased to avoid the click-on noise.