Audio Amplifier Close-Down Timing for Pop Noise Reduction
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Solution Overview
Problem
Audio power conversion systems often experience audible 'pop' noise during close-down due to energy stored in demodulation filters and non-controllable MOSFET conduction, which existing solutions have not adequately addressed.
Innovation Solution
A close-down reduction system for audio amplifiers that involves increasing the switch frequency by slowly removing a pole in the feedback filter and disabling the power stage at a specific point in the PWM pulse, while using a close-down timing circuit to optimize the timing for minimizing energy in the demodulation filter and reducing audible noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the power stage is disabled during close-down, then the amplifier stops amplifying signals, but audible pop noise occurs due to stored energy in the demodulation filter and non-controllable MOSFET conduction
Solution Approach 1:
The feedback pole is removed in advance before disabling the power stage. This preliminary action reduces the energy stored in the demodulation filter to minimal levels, ensuring that when the power stage is subsequently disabled, there is insufficient energy to generate audible pop noise at the output.
Solution Approach 2:
The feedback filter dynamically changes its characteristics during close-down by removing a pole. This dynamic adjustment optimizes the filter's energy dissipation behavior, transitioning from normal operation to close-down mode to minimize residual energy and prevent pop noise.
2Object-generated harmful factors
If the switch frequency is increased during close-down, then the energy in the demodulation filter is reduced, but the close-down timing becomes more critical
Solution Approach 1:
The switch frequency is dynamically changed during close-down by removing a feedback pole. This parameter change increases the switching frequency temporarily, which accelerates the decay of energy in the demodulation filter. The timing is optimized to achieve minimal energy before power stage disablement.
3Loss of energy
If MOSFETs are turned off during close-down, then power consumption is reduced, but non-controllable conduction causes pop noise
Solution Approach 1:
The feedback pole removal is performed in advance of MOSFET shutdown. This preliminary action ensures that by the time MOSFETs are turned off and power consumption is minimized, the energy in the system is already reduced to levels that prevent audible pop from non-controllable conduction.
Data Source
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AI summary
A close-down pop reduction system and a method for close-down pop reduction in an audio amplifier assembly are disclosed. The switching power conversion system comprises a forward path having a compensator and a switching power stage and a signal path from an output of a comparator in the switching power stage to a sequence control unit. The signal path includes a close-down timing circuit configured to provide a timing signal. The sequence control unit is configured to eliminate the input signal, increase the switch frequency of the close-down pop reduction system and disable the switching power stage at a moment in time within a PWM pulse of the switching power stage. Hereby, it is e.g. possible to minimize the audible pop during close- down of audio amplifier assemblies.