Differential Audio Amplifier Common-Mode Buffer for Pop-Free Startup
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Solution Overview
Problem
Audio amplifier circuitry experiences audible artefacts like popping sounds due to voltage transitions at output nodes during start-up and shut-down when operating without a negative power supply, affecting user experience.
Innovation Solution
Incorporation of common mode buffer circuitry and low pass filter circuitry to selectively output a common mode voltage to the output nodes, along with dummy and real output stages and feedback paths, to minimize differential transients and maintain output nodes at a common mode voltage during power states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the amplifier circuitry operates without a negative power supply and uses a common mode voltage, then the device complexity is reduced, but audible artefacts like popping sounds occur during start-up and shut-down
Solution Approach 1:
The common mode buffer circuitry is enabled before the main amplifier circuitry during start-up, pre-establishing the common mode voltage at the output nodes. This preliminary action ensures that when the amplifier switches on, the output nodes are already at the correct voltage level, preventing popping sounds. Similarly, during shut-down, the buffer remains enabled to maintain voltage until the amplifier is fully off.
Solution Approach 2:
The common mode buffer circuitry acts as an intermediary between the power supply and the output nodes. It selectively couples the common mode voltage to the output nodes through switch circuitry, mediating the voltage transition during start-up and shut-down. This intermediary buffer isolates the output nodes from direct voltage changes, preventing audible artefacts.
2Ease of operation
If the amplifier circuitry transitions voltage at output nodes during start-up and shut-down, then the amplifier can power on and off, but voltage transitions cause audible artefacts
Solution Approach 1:
During start-up, the common mode buffer is enabled in advance to establish the common mode voltage at output nodes before the main amplifier becomes active. During shut-down, the buffer remains enabled to maintain voltage until the amplifier is fully deactivated. This preliminary and sustained action prevents voltage transitions that would cause popping sounds while maintaining full power on/off capability.
Solution Approach 2:
The circuit uses switching control to change the operational state of the common mode buffer and its coupling to output nodes. By controlling the buffer's enable state and coupling switches, the system maintains voltage at output nodes during critical transition periods, preventing audible artefacts while allowing normal power cycling operation.
3Object-generated harmful factors
If the common mode buffer circuitry is used to maintain output nodes at common mode voltage, then audible artefacts are reduced, but the device complexity increases
Solution Approach 1:
The common mode buffer circuitry serves multiple functions: it generates the common mode voltage, buffers it to maintain stability, and selectively couples it to output nodes through switch circuitry. This multi-functional design reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall device complexity while effectively preventing audible artefacts.
4Productivity
If the amplifier circuitry quickly re-enables output stages when input signal is received, then productivity is improved, but voltage transitions may cause audible artefacts
Solution Approach 1:
When an input signal is received, the common mode buffer is enabled in advance to establish the common mode voltage at output nodes before the main amplifier output stages are activated. This preliminary voltage establishment ensures that when the output stages quickly switch on, no voltage transition occurs at the output nodes, preventing popping sounds while maintaining fast re-enablement capability.
Solution Approach 2:
The common mode buffer maintains continuous voltage at the output nodes throughout the re-enablement process. By keeping the buffer enabled and coupled during the transition period, the system ensures uninterrupted voltage supply, eliminating gaps or transitions that would cause audible artefacts while allowing rapid activation of the output stages.
Data Source
AI summary
The present disclosure relates to circuitry comprising audio amplifier circuitry for receiving an audio signal to be amplified; and first and second output nodes for outputting first and second differential output signals. The circuitry further comprises common mode buffer circuitry configured to receive a common mode voltage and to selectively output the common mode voltage to the first and second output nodes.