Amplifier Power-Up Sequencing to Eliminate Click and Pop Noise
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Solution Overview
Problem
Existing audio amplifiers experience 'click 'n pop' noise due to transient signals when power is switched on or off, which is difficult to mitigate in small equipment without using relays or transistors that cause additional cost, complexity, and distortion.
Innovation Solution
An amplifier design featuring a main and auxiliary amplification stage with sequential power control and switch management, where the auxiliary stage establishes a quiescent voltage before powering the main stage, reducing transient signals by initially coupling the output to a reference voltage and then de-coupling it, and using an auxiliary feedback arrangement for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If relays are used to isolate the loudspeaker from the amplifier until after power is supplied, then click 'n pop' noise is reduced, but device complexity, size, and cost increase
Solution Approach 1:
The patent replaces the mechanical relay system with an electronic switching mechanism using transistors (specifically MOSFETs) controlled by voltage signals. The switching function is achieved through electronic control of transistor gate voltages rather than mechanical relay actuation, eliminating the mechanical components while maintaining the isolation function during power-up and power-down sequences.
Solution Approach 2:
The patent introduces an intermediary control circuit that manages the power supply sequencing to the amplifier stages. This control circuit acts as a mediator between the power source and the amplifier stages, ensuring that power is supplied in the correct sequence (auxiliary stage first, then main stage) to prevent click 'n pop' noise without requiring mechanical isolation devices.
2Device complexity
If transistors are used to perform the switching function, then device size and cost are reduced, but distortion is introduced
Solution Approach 1:
The patent applies preliminary action by establishing the quiescent voltage at the common node using the auxiliary amplification stage before the main amplification stage is activated. This preparatory step ensures that when the main stage power is switched on, the voltage transitions are minimized because the output node is already at the correct reference voltage level, preventing distortion during the power-up transient.
Solution Approach 2:
The patent divides the amplification function into two separate stages: an auxiliary amplification stage and a main amplification stage. The auxiliary stage is responsible for establishing the quiescent voltage at the common node, while the main stage handles the primary signal amplification. This segmentation allows the switching transients to be isolated to the auxiliary stage without affecting the main signal path, thereby reducing distortion.
3Ease of operation
If power is switched on when the loudspeaker is already connected, then ease of operation is improved, but click 'n pop' noise occurs
Solution Approach 1:
The patent maintains continuity of useful action by keeping the auxiliary amplification stage active and establishing the quiescent voltage continuously at the common node. This continuous preparation ensures that when the main amplification stage is powered on, the voltage transition is smooth and continuous rather than abrupt, eliminating transient signals while allowing the power supply to be switched on with the loudspeaker already connected.
Solution Approach 2:
The patent applies preliminary anti-action by using the auxiliary amplification stage to pre-establish the correct quiescent voltage at the common node before the main amplification stage is activated. This preliminary voltage establishment counteracts the potential transient signals that would otherwise occur during power-up, preventing click 'n pop' noise while allowing convenient power supply timing.
Data Source
AI summary
An amplifier comprises a main amplification stage and an auxiliary amplification stage. An input of the main amplification stage and an input of the auxiliary amplification stage are coupled to a common node, and an output of the main amplification stage is coupled to an output node. During activation, before power is supplied to the main amplification stage, the output node is coupled to a reference voltage (VREF). A quiescent voltage is then established at the common node by coupling power to the auxiliary amplification stage. Only then is power coupled to the main amplification stage and the reference voltage (VREF) de-coupled from the output node.