Audio Amplifier Startup Biasing to Minimize Pop Noise
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Audio power conversion systems often experience audible 'pop' at startup due to transients when the control system starts from a saturated position, and existing solutions are complex or limited to specific digital systems.
Innovation Solution
A switching power conversion system where the output of the compensator is connected to the input of the DC servo before the power stage startup, allowing correct biasing and using a pre-charge circuit for the bootstrap capacitor to enable a high or low first pulse without generating an audible 'pop', along with a switch to connect or disconnect the DC servo from the compensator output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the control system starts up from a saturated position, then the power stage can be quickly activated, but an audible 'pop' signal is generated at the output
Solution Approach 1:
The patent applies preliminary action by connecting the compensator output to the DC servo input before the power stage startup. This allows the control system to be correctly biased in advance, preventing saturation and eliminating the audible pop signal during startup while maintaining quick activation
2Object-generated harmful factors
If a parallel power stage with switch is added to minimize close down pop, then the pop signal is reduced, but the system complexity increases
Solution Approach 1:
The patent makes the existing DC servo circuit perform multiple functions: it handles both normal operation and startup biasing by receiving input from either the amplifier output or compensator output. This eliminates the need for separate parallel power stages while maintaining pop reduction capability
Solution Approach 2:
The patent introduces a switch as an intermediary element that selectively connects the DC servo to different sources (amplifier output or compensator output). This simple switching mechanism enables the system to minimize pop signals without adding complex parallel power stages
3Object-generated harmful factors
If a serial resistor is used for ramping up, then the startup pop is minimized, but the solution is not applicable to systems with control loops
Solution Approach 1:
The patent utilizes the existing feedback path in control loop systems by routing the compensator output to the DC servo input. This approach is specifically designed for systems with control loops, making the solution highly adaptable while effectively minimizing startup pop through the feedback mechanism
4Speed
If the bootstrap capacitor is charged with a forced width low pulse, then the power stage can start up, but an audible 'pop' is generated
Solution Approach 1:
The patent applies preliminary action by pre-charging the bootstrap capacitor through the DC servo before the power stage activation pulse is applied. This preliminary charging eliminates the need for forced width low pulses, allowing the power stage to start up with either high or low pulses without generating audible pop signals
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3b
AI summary
A switching power conversion system and a method for start-up pop minimization in an audio amplifier assembly are disclosed. The switching power conversion system comprises a forward path including a compensator, a switching power stage and a demodulation filter. The system further comprises a DC-servo and a pre-charging circuit and a sequence control unit configured for providing a start-up sequence where the compensator and DC-servo are correctly biased and a bootstrap capacitor within the switching power stage is charged before the switching power stage is started. Hereby, it is e.g. possible to minimize the audible start-up pop in audio amplifier assemblies.