Duty-Cycle Audio Amplifier Gain Control for Pop Noise Suppression
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Solution Overview
Problem
Existing audio power amplifier circuits produce 'pop' noise when powered on or off, which can damage speakers and discomfort users, necessitating effective noise suppression.
Innovation Solution
A duty cycle modulation circuit is introduced to control the gain of the audio power amplifier by adjusting the duty cycle of a high frequency switch, using a first and second counting module, logic output module, and detection modules to generate switch modulation signals that gradually change the duty cycle during power transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the audio power amplifier circuit is powered on or off suddenly, then the power amplifier can quickly start or shut down, but 'pop' noise is generated that can damage speakers and discomfort users
Solution Approach 1:
The patent applies preliminary action by introducing a duty cycle modulation circuit that gradually adjusts the gain of the amplifier before full power operation is engaged. During power-on, the circuit slowly increases the duty cycle from 0% to 100% over a predetermined period, and during power-off, it gradually decreases the duty cycle from 100% to 0%, preventing sudden voltage changes that cause pop noise while still achieving quick overall startup and shutdown.
Solution Approach 2:
The patent applies dynamics by making the duty cycle of the high-frequency switch dynamically adjustable rather than fixed. The duty cycle modulation circuit continuously varies the duty cycle based on the power state, transitioning smoothly between states to eliminate abrupt changes in amplifier gain that would generate harmful pop noise, while maintaining the ability to quickly respond to power on/off commands.
2Object-affected harmful factors
If a duty cycle modulation circuit is introduced to suppress pop noise, then pop noise is effectively reduced, but the circuit complexity increases
Solution Approach 1:
The patent applies universality by designing the duty cycle modulation circuit to perform multiple functions simultaneously: it suppresses pop noise during power transitions, maintains circuit linearity, and enables gradual gain adjustment. The same circuit structure handles both power-on and power-off scenarios, and the counting modules serve dual purposes of timing control and duty cycle generation, reducing the need for separate dedicated circuits for each function.
Solution Approach 2:
The patent applies nested doll by integrating the duty cycle modulation functionality within the existing amplifier structure. The high-frequency switch is nested within the second-stage integral amplifier, and the counting modules are nested within the duty cycle modulation circuit, creating a compact hierarchical structure where smaller functional blocks are contained within larger systems, minimizing overall circuit complexity while achieving pop noise suppression.
Data Source
AI summary
An audio power amplifier circuit and a duty cycle modulation circuit and a noise suppression circuit thereof are disclosed. The audio power amplification circuit includes an integral amplifier module and a high frequency switch The duty cycle modulation circuit is used to adjusts a gain of the audio power amplifier circuit by controlling a duty cycle of the high frequency switch. The duty cycle modulation circuit counts pulses of a duty cycle modulation signal to obtain a first count value counts pulses of a clock signal to obtain a second counting value and performs a logical operation according to the first count value, the second count value, and the clock signal to obtain a switch modulation signal for controlling the high frequency switch. The “pop” noise is weakened by controlling the gain of the audio power amplifier circuit, and the cost is reduced while meeting the high linearity of the circuit.