Audio Power Stage Output Equalization During Startup Voltage Ramping
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Solution Overview
Problem
Audio systems often experience undesirable audible pop sounds during startup or reset due to transient voltage differences across speaker terminals, caused by asymmetries in power stages and rapid voltage ramping.
Innovation Solution
The implementation of a control circuit that sets the outputs of first and second power stage circuits to specific voltages when the supply voltage is below a threshold, using assist transistors to manage the voltage ramping and reduce transient differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the audio amplifier rapidly ramps up voltage during startup or reset, then the system responds quickly and becomes operational faster, but transient voltage differences are generated across speaker terminals causing audible pop sounds
Solution Approach 1:
The control circuit proactively detects when the audio amplifier is in a powered-off state (cold start or reset) and preemptively prevents transient voltage differences by controlling the power stage outputs to remain equalized before normal operation begins. This preliminary action eliminates the pop sound condition before it can occur during the startup transition.
Solution Approach 2:
The control circuit acts as an intermediary between the power supply and the audio amplifier power stages. It monitors the powered-off condition and mediates the voltage transition by ensuring both power stage outputs remain equalized during startup, thereby preventing the direct transmission of transient voltage differences to the speaker terminals.
2Reliability
If the audio amplifier is powered up from a powered-off state, then the system becomes operational, but transient signals are transmitted to the speaker causing voltage differences and audible pops
Solution Approach 1:
The control circuit continuously monitors the operational state of the audio amplifier and provides feedback control during the powered-off to powered-on transition. By detecting the powered-off condition and actively controlling the power stage outputs to remain equalized, the feedback mechanism ensures that transient voltage differences do not develop across the speaker terminals during startup.
Solution Approach 2:
Before the audio amplifier fully transitions from powered-off to operational state, the control circuit preemptively equalizes the power stage outputs to prevent transient voltage differences. This preliminary equalization action occurs during the transition period, ensuring that when the amplifier becomes operational, no harmful transients are present at the speaker terminals.
Data Source
AI summary
An apparatus includes a first power stage circuit having a first output and a power terminal, and a second power stage circuit having a second output and the power terminal. The apparatus further includes a control circuit having a control input, a first control output, and a second control output. In an example, the control input is coupled to the power terminal, the first control output is coupled to the first output, and the second control output is coupled to the second output. In an example, the control circuit is configured to, responsive to a first voltage at the power terminal being below a threshold voltage, set the first and second outputs to a second voltage.