Automatic Level Control Circuit Using Triode-Region MOSFET Resistance
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Solution Overview
Problem
Class AB amplifiers in audio applications suffer from low efficiency, leading to increased power dissipation, heat sink requirements, and higher costs, while class D amplifiers offer higher efficiency but often result in high distortion.
Innovation Solution
A low distortion automatic level control circuit using a variable resistance circuit with MOSFETs biased in the triode region, coupled with an op-amp and resistance circuits, to provide a voltage-controlled amplifier with minimal distortion and efficient power management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If class AB amplifiers are used to drive speaker load, then linearity and low distortion are achieved, but power efficiency is low leading to increased power dissipation and heat sink requirements
Solution Approach 1:
The patent implements dynamic class switching between class AB and class D operation modes based on signal conditions. The amplifier automatically transitions from class AB (for low distortion) to class D (for high efficiency) when the signal level exceeds a threshold, resolving the contradiction between linearity and power efficiency through adaptive operation
Solution Approach 2:
The invention changes the operational parameters of the amplifier by switching between different conduction angles and operating modes. By adjusting the class of operation dynamically, the system optimizes the trade-off between distortion performance and power efficiency according to the instantaneous signal requirements
2Loss of energy
If class D amplifiers are used to improve power efficiency, then battery life is extended and heat sink requirements are eliminated, but distortion increases
Solution Approach 1:
The system dynamically switches between class D and class AB modes based on signal amplitude. At low signal levels where class D operation would produce excessive distortion, the amplifier transitions to class AB mode, thereby maintaining low distortion while preserving the power efficiency benefits of class D operation during high-level signals
Solution Approach 2:
The patent introduces an intermediary control mechanism that monitors signal levels and orchestrates the transition between amplifier classes. This intermediary control system ensures that the benefits of both class D (efficiency) and class AB (low distortion) are achieved by appropriately selecting the operating mode based on real-time signal conditions
3Volume of moving object
If class D amplifiers are used for high-power audio systems, then compact design and low cost are achieved, but thermal runaway concerns increase
Solution Approach 1:
The patent employs thermal runout protection circuitry as an intermediary safety mechanism that monitors and controls the thermal state of the amplifier. This protection system enables the use of compact class D designs by providing automated thermal management and preventing thermal runaway conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves efficient power management, reduces distortion, and maintains sound quality by using MOSFETs in the triode region for variable resistance control, allowing for compact, low-cost, high-power audio systems without the need for heat sinks.
Implementation Method 1
A low distortion automatic level control circuit using a variable resistance circuit with MOSFETs biased in the triode region
Data Source
AI summary
A circuit and method for automatic level control is provided. The circuit includes an amplifier including a variable resistance circuit that is connected between a first node and a second node. The circuit also includes a first resistance circuit that is connected between a first input node and the first node, and a second resistance circuit that is connected between the first input node and a first op amp node. The first and second resistance circuits are at least approximately linear elements. The circuit also includes an op amp having at least a first input that is connected to the first op amp input node.