Variable-Resistor Anti-Pop Circuit for Audio Amplifier Switching
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Solution Overview
Problem
Audio amplifiers experience unwanted pops during power-up, power-down, and state transitions, which can damage equipment and pose a risk to hearing due to the generation of impulses.
Innovation Solution
The implementation of anti-pop circuits using a variable resistor and capacitor connected to the audio amplifier, with field effect transistors responsive to the virtual analog ground voltage, providing a low-pass filter and a power-down field effect transistor to control the gain, effectively reducing pops by varying resistance and gain in response to voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the audio amplifier is turned on or off quickly, then the amplifier responds faster and is more efficient, but pops are generated that can damage equipment and user hearing
Solution Approach 1:
The anti-pop circuit performs preliminary actions by gradually ramping up the power supply voltage before the amplifier is fully activated, and by gradually discharging capacitors before power-down. This preliminary voltage control prevents sudden voltage transitions that cause pops, allowing the amplifier to switch states safely without generating harmful noise.
Solution Approach 2:
The circuit uses capacitors and resistors to create a cushioning effect during voltage transitions. The capacitors store and release energy gradually, while the resistors limit current spikes, thereby cushioning the voltage transitions and preventing the generation of pop noises that could damage equipment or hearing.
2Object-affected harmful factors
If a fixed resistor and capacitor are used to reduce pops, then pops are reduced, but the circuit complexity increases and the solution is not adaptive to varying voltage conditions
Solution Approach 1:
The patent replaces fixed resistors and capacitors with dynamic components whose values change during operation. The resistor's resistance and the capacitor's capacitance are dynamically adjusted based on the instantaneous voltage level, allowing the circuit to adapt to varying voltage conditions during power-up and power-down, thereby reducing pops without requiring overly complex fixed-value component networks.
Solution Approach 2:
The circuit changes the parameters of the resistor and capacitor during operation. The resistance value varies with voltage during power-up, and the capacitance varies during power-down, allowing the anti-pop circuit to maintain optimal performance across different voltage conditions without increasing overall circuit complexity.
3Device complexity
If the resistor value is kept constant, then the circuit is simpler, but pops cannot be effectively reduced during voltage transitions
Solution Approach 1:
The resistor's resistance parameter is changed dynamically during power-up based on the instantaneous voltage level. This parameter change allows the circuit to effectively suppress pops during voltage transitions while maintaining relative circuit simplicity, as the dynamic behavior is achieved through voltage-dependent resistance rather than complex control logic.
4Device complexity
If the capacitor value is kept constant, then the circuit is simpler, but pops cannot be effectively reduced during power-down transitions
Solution Approach 1:
The capacitor's capacitance parameter is changed dynamically during power-down based on the instantaneous voltage level. This allows the circuit to effectively reduce pops during power-down transitions while maintaining relative simplicity, as the dynamic capacitance is achieved through voltage-dependent behavior rather than complex control mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces or eliminates pops during power-up and power-down cycles, ensuring the safety of equipment and user hearing by using a low-pass filter and controlled gain mechanisms.
Implementation Method 1
The variable resistor has resistance that varies in response to a voltage level of the virtual analog ground. In some embodiments, the voltage level of the virtual analog ground is a difference between a voltage level of the power supply voltage and the voltage level of the virtual analog ground.
Implementation Method 2
These anti-pop circuits comprise a variable resistor and a capacitor that are connected to the audio amplifier to provide a low pass filter.
Implementation Method 3
a variable resistor and a capacitor that are connected to the audio amplifier to provide a low pass filter
Implementation Method 4
an anti-pop circuit also includes a power-down field effect transistor that is connected to the audio amplifier, and that has a gain that varies in response to the voltage level of the virtual analog ground
Data Source
AI summary
Anti-pop circuits are provided for an audio amplifier that uses a power supply voltage and a ground voltage to drive a load with an audio signal that is centered about a virtual analog ground. These anti-pop circuits include a variable resistor and a capacitor that are connected to the audio amplifier to provide a low pass filter. The variable resistor has resistance that varies in response to a voltage level of the virtual analog ground, such as a difference between a voltage level of the power supply voltage and the voltage level of the virtual analog ground. The variable resistor may be a field effect transistor having a gate that is responsive to the differences between the voltage level of the power supply voltage and the voltage level of the virtual analog ground. The capacitor may be a field effect transistor, as well. Related methods are also described.