Audio Amplifier Capacitor Precharge for Turn-On Pop Noise
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Solution Overview
Problem
Existing audio amplifiers experience turn-on and turn-off transients that result in noise issues, such as clicks or pops, degrading their usability.
Innovation Solution
An audio amplification circuit is designed with a charging mode that equally charges capacitors to minimize transients, using a configuration with transconductance amplifiers, current sources, and control logic to manage bias and reference voltages, ensuring equal gains and settling delays to reduce noise during startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional audio amplifiers are used to amplify audio signals, then audio output is achieved, but turn-on and turn-off transients produce audible click or pop noises
Solution Approach 1:
The patent applies preliminary action by charging the input capacitors of the differential amplifiers through a current source before enabling the amplifiers to operate. This pre-charging process ensures that the capacitors are equally charged to the bias voltage level before the amplifiers are activated, preventing transient imbalances that would cause click or pop noises during turn-on. The control logic monitors the charging completion and only enables the amplifiers after the capacitors are sufficiently charged.
Solution Approach 2:
The patent implements feedback through control logic that monitors the voltage levels on the input capacitors and uses this information to control the enabling of the differential amplifiers. The control logic receives feedback about the capacitor charging status and adjusts the amplifier enable signals accordingly, ensuring that amplifiers are only enabled when the capacitors are properly charged, thus preventing transient noise.
2Speed
If amplifiers are enabled immediately upon power-up, then quick startup is achieved, but transient noise occurs due to unequal capacitor charging
Solution Approach 1:
The patent applies preliminary action by charging the input capacitors through a dedicated current source path before enabling the amplifiers. This pre-charging phase occurs automatically upon power-up and completes in a controlled manner, ensuring capacitors are ready before the amplifiers are activated. The control logic detects when charging is complete and immediately enables the amplifiers, achieving fast startup without transient noise.
Solution Approach 2:
The patent segments the startup process into distinct phases: a pre-charging phase where only the capacitors are charged through the current source, and an operational phase where the amplifiers are enabled. This segmentation is controlled by control logic that manages the timing and sequencing of different circuit components, allowing the capacitors to be charged independently before the amplifiers are activated, thus preventing transient noise while maintaining fast startup.
3Power
If differential amplifiers are used to drive the speaker, then audio amplification is achieved, but turn-off transients also produce click or pop noises
Solution Approach 1:
The patent applies preliminary action in reverse for turn-off by disabling the amplifiers before disconnecting the power supply. The control logic detects when the audio signal should be terminated and disables the amplifiers in advance, allowing the output capacitors to discharge through the load rather than being abruptly disconnected. This prevents the voltage spikes and transient noise that would occur with immediate power cutoff.
Solution Approach 2:
The control logic uses feedback about the audio signal status and amplifier operation to manage the turn-off sequence. When the audio signal is terminated or muted, the control logic receives feedback and initiates the amplifier disable sequence, ensuring that amplifiers are turned off in a controlled manner that prevents turn-off transients, while maintaining full audio amplification capability during normal operation.
Data Source
AI summary
In one embodiment, an amplification circuit charges a filter capacitor (14) and an input capacitor (12) with a substantially constant current and subsequently forms a delay prior to operating the amplification circuit to amplify input signals.