Audio Power Stage Output Control for Startup Pop Reduction
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Solution Overview
Problem
Audio systems often produce an undesirable audible pop sound during startup or reset due to transient voltage differences across the speaker terminals, which can occur when the supply voltage ramps up and the audio signals have not yet been provided to the amplifiers.
Innovation Solution
The implementation of a control circuit that manages the power stage circuits and speaker terminals, setting the outputs to specific voltages when the supply voltage is below a threshold, thereby minimizing transient voltage differences and reducing the likelihood of pop noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the supply voltage ramps up quickly during startup, then the system can start faster, but transient voltage differences are generated across speaker terminals causing audible pop sounds
Solution Approach 1:
The control circuit performs preliminary action by detecting when the supply voltage is below a threshold during startup and actively setting the output voltages of the first and second power stage circuits to matched values before normal operation begins. This preliminary voltage matching prevents transient voltage differences across the speaker terminals that would otherwise cause audible pop sounds, allowing the system to start quickly without noise.
2Device complexity
If the output voltages of power stage circuits are allowed to float during startup, then the circuit operation is simpler, but transient signals are transmitted to the speaker causing audible pops
Solution Approach 1:
The control circuit acts as an intermediary between the power stage circuits and the speaker during startup. It monitors the supply voltage and actively controls the output voltages of the power stage circuits to ensure they remain matched, thereby preventing transient signals from reaching the speaker. This intermediary control adds minimal complexity while effectively eliminating pop noise.
3Ease of manufacture
If no voltage control is applied during startup, then the system is easier to manufacture, but transient voltage differences produce audible pop sounds
Solution Approach 1:
The control circuit provides self-service by automatically detecting the supply voltage level and adjusting the output voltages of the power stage circuits without external intervention. During startup, it autonomously ensures voltage matching to prevent pop noise, and during normal operation, it transitions to standard audio signal processing. This self-managing approach maintains manufacturing simplicity while eliminating the pop noise problem.
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.