Headset Amplifier Power Sequencing for Pop Noise Suppression
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Solution Overview
Problem
Audio amplifiers in headsets suffer from annoying 'pop' noises during power application and removal, particularly in mobile processing device applications, due to excessive settling times and the need for external filtering capacitors, which increase cost and power consumption.
Innovation Solution
A fully integrated headset amplifier design with a low-gain first amplifying stage and a higher-gain second stage, using a sample-and-hold circuit and series-parallel feedback to control power application and removal, eliminating the need for external filtering capacitors and reducing power-up and power-down noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an external filtering capacitor is used to reduce popping noises, then the popping noise is reduced, but the device complexity increases and integration is not achieved
Solution Approach 1:
The patent merges the filtering function with the existing AC coupling capacitor by using it in a track-and-hold configuration. The AC coupling capacitor serves dual purposes: AC coupling and pop noise filtering, eliminating the need for separate external filtering components and achieving full integration.
Solution Approach 2:
The AC coupling capacitor is made multi-functional by using it both for AC coupling and for filtering pop noise through the track-and-hold circuit. This universal usage eliminates the need for dedicated external filtering capacitors, reducing component count and achieving integration.
2Loss of time
If a large external capacitor is used for filtering, then the settling time is reduced, but the device cannot be fully integrated on the integrated circuit
Solution Approach 1:
The filtering function is merged with the AC coupling capacitor, allowing the use of a small on-chip capacitor instead of a large external capacitor. The track-and-hold circuit compensates for the smaller capacitance value, enabling full integration while maintaining acceptable settling time.
Solution Approach 2:
The patent changes the operating parameters of the AC coupling capacitor by using it in a track-and-hold configuration rather than a simple RC filter. This allows the capacitor to function effectively with a much smaller value, enabling on-chip integration while still achieving adequate filtering and settling characteristics.
3Use of energy by moving object
If power is frequently switched on and off to reduce power consumption, then power consumption is reduced, but popping noises occur during power transitions
Solution Approach 1:
The track-and-hold circuit performs preliminary action by pre-charging the AC coupling capacitor to the output voltage level before power is fully applied to the amplifier. This prevents voltage transients and popping noises during power-on, while still allowing frequent power cycling to save energy.
Solution Approach 2:
The circuit applies preliminary anti-action by using the hold capacitor to counteract voltage changes at the output during power transitions. The hold capacitor maintains the output voltage level during power-off and recharges it during power-on, preventing the voltage transients that cause popping noises.
4Object-affected harmful factors
If the AC coupling capacitor is charged during power-up, then popping noise is prevented, but the power-down time increases
Solution Approach 1:
The track-and-hold circuit performs preliminary action by pre-charging the AC coupling capacitor to the correct voltage level before power is fully applied. This eliminates the need for lengthy charging periods during normal operation, as the capacitor is already charged and ready to prevent popping noises.
Solution Approach 2:
The circuit uses periodic action by cycling the power to the amplifier stages in a controlled sequence. The first stage is powered on to charge the hold capacitor, then the second stage is powered on, creating a periodic power application pattern that prevents popping without requiring extended charging times.
Data Source
AI summary
An amplifier (50) for voice or audio signals, and particularly for headset applications, uses a low gm amplifier (54) for initially charging an output node (OUT) at the beginning of a power-on phase. After charging the output node, a main amplifier (56) is enabled to amplify the voice or audio signal. At power-down, a sample-and-hold circuit (58) drives an output transistor to discharge an AC coupling capacitor (20). Thus, spikes at the output node are eliminated and an external filtering capacitor is not needed.