Dual-Threshold Audio Level Control Circuit for Noise Suppression
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Solution Overview
Problem
Conventional automatic level control (ALC) circuits in audio systems often amplify noise when the input signal is low, leading to poor audio quality and inability to adjust volume flexibly across varying signal levels.
Innovation Solution
An ALC circuit with a variable gain amplifier and dual control units that set the gain to a fixed value when the input signal is below a threshold, disabling noise amplification, and dynamically adjust the gain based on output signal levels to maintain a constant output level, incorporating a sub-amplifier and output mixing unit to further manage signal levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the gain of the variable gain amplifier is increased to amplify quiet sounds, then the level of quiet sound is raised, but noise is also amplified unnecessarily
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the gain parameter of the variable gain amplifier based on the detected signal level. When the input signal level exceeds the minimum threshold, the gain is increased to amplify quiet sounds; when the signal level falls below the threshold, the gain is reduced to a predetermined value to prevent noise amplification. This dynamic parameter adjustment resolves the contradiction between amplifying quiet sounds and avoiding noise amplification.
2Adaptability or versatility
If the gain is dynamically adjusted to maintain constant output level, then the volume control flexibility is improved, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the control function into two distinct control units: a first control unit that monitors input signal level and controls gain based on minimum threshold, and a second control unit that monitors output signal level and controls gain based on maximum threshold. This segmentation allows each control unit to handle specific aspects of volume control independently, improving flexibility while managing complexity through functional division.
Solution Approach 2:
The variable gain amplifier serves multiple functions: it amplifies quiet sounds when needed, maintains constant output level across varying input levels, and prevents noise amplification when input signal is below threshold. By making this single component multi-functional through the control units, the system achieves volume control flexibility without proportionally increasing overall device complexity.
Data Source
AI summary
A variable gain amplifier amplifies an input audio signal. A first control unit monitors the level of the input audio signal, and sets the gain of the variable gain amplifier to a predetermined fixed value when this level is lower than a predetermined minimum threshold. A second control unit monitors the level of an output signal VO of the variable gain amplifier. When this level exceeds a predetermined maximum threshold, the second control unit lowers the gain of the variable gain amplifier. When this level becomes smaller than this threshold, it raises the gain. When the level of the input audio signal is smaller than the minimum threshold, the first control unit disables the gain control operation of the variable gain amplifier controlled by the second control unit. A sub-amplifier amplifies the input audio signal. An output mixing unit mixes signals output from the variable gain amplifier and the sub-amplifier.