Audio Output Driver with Virtual Ground Pop Noise Suppression
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Solution Overview
Problem
Audio devices often generate noise transients, such as 'pops', when turned on or off, which can be disagreeable to users and potentially damage audio output devices, highlighting the need for noise-free audio output circuitry that can be efficiently implemented in integrated circuits.
Innovation Solution
The implementation of an audio output driver that includes a virtual ground generator and voltage equalizer, which generates a virtual ground signal that drives the audio output device with inaudible frequencies when power is removed, and a recharge limiter that limits the recharge rate during power-up to avoid transient signals, along with an amplifier controller that monitors supply voltage to prevent noise and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If audio output circuitry is turned on or off, then power is saved and device is ready for use, but noise transients such as pops are generated
Solution Approach 1:
The virtual ground generator is activated before the audio amplifier during power-up to pre-establish a stable reference voltage. This preliminary action ensures that when the amplifier switches on, there is no sudden voltage differential that would cause a pop noise transient.
Solution Approach 2:
The virtual ground signal acts as an intermediary between the power supply and the audio output device. By introducing this intermediate reference voltage that tracks the supply voltage, the circuit avoids direct switching transients from reaching the output, thereby eliminating pops while maintaining power efficiency.
2Productivity
If recharge rate during power-up is increased, then device is ready faster, but transient signals are generated
Solution Approach 1:
The recharge rate of the virtual ground capacitor is dynamically controlled through a switch that connects different resistor values. During initial power-up, a higher recharge rate is permitted once the virtual ground voltage reaches a threshold, optimizing the balance between speed and transient prevention.
Solution Approach 2:
The power-up sequence is divided into distinct phases: an initial slow recharge phase that prevents transients, followed by a faster recharge phase that accelerates readiness. This periodic control of the recharge rate eliminates harmful transients while minimizing overall power-up time.
Data Source
AI summary
An audio output driver includes an audio amplifier for generating an amplified signal. A virtual ground generator generates a virtual ground signal in response to a virtual ground reference. A combiner produces an output signal, based on the amplified signal and the virtual ground signal, that is coupled to an audio output device. A voltage equalizer equalizes the virtual ground reference and the output signal when the supply voltage compares unfavorably to a supply voltage threshold.