Audio Output Circuit Timing for Pop Noise Suppression
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Solution Overview
Problem
Conventional audio output devices require large layout areas and additional external components to prevent pop noise due to the need for high-pass filters and complex control circuits, making them inefficient in terms of size and complexity.
Innovation Solution
An audio output device with a digital/analog converter, non-inverting amplifier, and inverting amplifiers that use logical enable signals to control the output timing, eliminating the need for AC-coupling capacitors and simplifying the circuit configuration, thereby reducing layout area and preventing pop noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coupling capacitors and high-pass filters are used to prevent pop noise, then pop noise is reduced, but layout area increases and external components are required
Solution Approach 1:
The patent extracts and removes the coupling capacitor from the circuit by implementing DC coupling between the D/A converter and amplifier. The pop noise prevention function is extracted from the capacitor and transferred to a control circuit that manages power supply timing, eliminating the need for the capacitor and reducing layout area.
Solution Approach 2:
The patent replaces the passive electrical component (coupling capacitor) with an active control system that manages power supply timing. The control circuit enables/disables the D/A converter and amplifier at specific timing to prevent DC offset voltage accumulation, substituting the mechanical/electrical capacitor-based solution with a control-based approach.
2Reliability
If control circuits are added to manage power-on/power-off timing, then pop noise is prevented, but device complexity increases
Solution Approach 1:
The patent merges the pop noise prevention function with the existing power management circuitry of the audio device. The control circuit that manages power-on/power-off timing is integrated into the overall system control, combining multiple functions (power management and pop noise prevention) into a unified control mechanism rather than adding a separate dedicated circuit.
Solution Approach 2:
The control circuit performs preliminary actions by enabling the D/A converter before the amplifier during power-on, and disabling them in reverse order during power-off. This preliminary timing control prevents DC offset voltage from accumulating in the amplifier, proactively preventing pop noise before it occurs rather than reacting to it.
3Reliability
If AC coupling is used to separate DC components, then DC offset voltage is blocked, but circuit complexity and component count increase
Solution Approach 1:
The patent extracts the DC blocking function from the coupling capacitor and relocates it to the control circuit timing mechanism. By controlling when the D/A converter and amplifier are enabled/disabled, the system prevents DC offset voltage from being transmitted to the amplifier output, removing the need for the capacitor while maintaining the DC blocking function.
Solution Approach 2:
The control circuit acts as an intermediary between the D/A converter and amplifier, managing the timing of their operation. This intermediary control prevents direct DC coupling issues by ensuring the D/A converter is fully powered on before the amplifier is enabled, and by coordinating their power-off sequence, thereby mediating the potential DC offset problem without requiring a physical coupling capacitor.
Data Source
AI summary
An audio output device and method capable of preventing generation of pop noise by a relatively simple and small-sized circuit configuration and control timing. A D/A converter converts a digital audio signal to an analog audio signal. A non-inverting amplifier amplifies the analog audio signal. A signal output from the non-inverting amplifier is amplified by inverting amplifiers of two stages with a first timing. A signal output from an inverting amplifier is input to a speaker amplifier by a switch. The output signal of the inverting amplifier is output to a speaker with a second timing subsequent to the first timing. The output signal of the inverting amplifier is amplified by the speaker amplifier and output to the speaker. With a third timing subsequent to the second timing, the output of each of the inverting amplifiers is stopped and the output of the speaker amplifier is stopped.