Reference Voltage Charging Control in Audio Amplifier Start-Up
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Solution Overview
Problem
Audio amplifiers generate unwanted transient signals, such as 'click' and 'pop', during power-up and power-down cycles due to rapid changes in the reference voltage, which are audible and problematic in both portable and non-portable applications, especially in single supply amplifiers.
Innovation Solution
An amplifier start-up apparatus with a charging control circuit that uses a positive feedback path to control the current flow to the capacitor in the reference voltage generator circuit, smoothing the rise of the reference voltage and minimizing slope discontinuities, thereby reducing audible transient signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reference voltage generator circuit is enabled during power-up, then the reference voltage is generated to enable the amplifier operation, but a transient signal is produced causing unwanted audible pops
Solution Approach 1:
The patent applies preliminary action by enabling the reference voltage generator circuit before enabling the amplifier. The reference voltage VMID is generated and stabilized first, allowing the amplifier to be enabled subsequently without producing transient signals. This sequence is controlled by control logic that manages the power-up timing of different circuit components.
Solution Approach 2:
The patent uses an intermediary approach by introducing a controlled switching mechanism between the reference voltage generator and the amplifier. The control logic acts as an intermediary that coordinates the enabling sequence, ensuring the reference voltage is ready before the amplifier operates, thereby preventing direct transient coupling.
2Use of energy by moving object
If the amplifier is powered down to reduce power consumption, then energy savings are achieved, but transient signals are generated during subsequent power-up
Solution Approach 1:
The patent applies preliminary action by maintaining or pre-charging the reference voltage generator circuit before disabling the amplifier during power-down mode. This ensures that when the amplifier needs to be re-enabled, the reference voltage is already available and stable, preventing transient signals during the power-up cycle while still allowing power savings during idle periods.
Solution Approach 2:
The patent uses dynamic control through control logic that adapts the power state of the reference voltage generator based on amplifier operation status. The system dynamically switches between power-saving mode and full operation mode, managing the transition to avoid transient signals while optimizing power consumption.
3Speed
If the reference voltage is charged rapidly during power-up, then the amplifier starts faster, but slope discontinuities cause audible pops
Solution Approach 1:
The patent applies periodic action by controlling the charging of the reference voltage in stages rather than as a single rapid charge. The control logic manages the power-up sequence to ensure smooth voltage transitions, effectively breaking down the charging process into controlled periods that avoid slope discontinuities while maintaining acceptable start-up speed.
Data Source
AI summary
An amplifier start-up apparatus for reducing transient signals in a circuit, for example an audio circuit, comprising a reference voltage generator circuit for generating a reference voltage. The reference voltage generator circuit comprises a capacitor for maintaining the reference voltage at a desired level. The amplifier start-up apparatus comprises a control circuit for controlling the operation of the reference voltage generator circuit during power-up. The control circuit comprises an amplifier with a positive feedback path for controlling a current flow to the capacitor.