Variable Time-Constant AGC Circuit for Stable Transimpedance Gain
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing automatic gain control (AGC) circuits in electronic circuits struggle to stabilize the control signal during payload periods while maintaining stability during preamble periods, leading to gain variations and instability, especially when input signals have varying amplitudes or long-continued high/low levels.
Innovation Solution
The electronic circuit incorporates a variable time constant control mechanism using a differential amplifier and a variable resistor to adjust the time constant of the hold circuit, allowing the bypass circuit to dynamically control the gain based on signal amplitude, switching between two time constants (τs and τl) to stabilize the control signal and adjust the amplifier gain accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fixed time constant is used in the hold circuit, then the control signal is stable during preamble periods, but gain variations occur during payload periods when input signals have varying amplitudes
Solution Approach 1:
The patent applies the dynamics principle by making the time constant of the hold circuit variable rather than fixed. The time constant control circuit dynamically adjusts the time constant between a first value (during preamble periods) and a second value (during payload periods) based on the operation period signal. This allows the system to maintain control signal stability during preamble periods while adapting gain control to varying input signal amplitudes during payload periods, thereby resolving the contradiction between stability and adaptability.
2Stability of the object's composition
If the time constant is increased to maintain stability during preamble periods, then control signal stability improves, but the response speed to input signal changes decreases
Solution Approach 1:
The patent implements dynamics by dynamically switching the time constant value based on the operation period. During preamble periods, a larger time constant is used to ensure control signal stability. During payload periods, a smaller time constant is used to enable faster response to input signal changes. The time constant control circuit switches between these two time constant values according to the operation period signal, thus resolving the contradiction between stability and response speed.
3Measurement precision
If a reset circuit is added to handle gain variations, then gain control accuracy improves, but device complexity increases
Solution Approach 1:
The patent avoids adding a separate reset circuit by dynamically adjusting the time constant of the existing hold circuit. The time constant control circuit generates appropriate control signals to switch the time constant value based on the operation period, which inherently handles gain variations without requiring additional reset functionality. This approach maintains gain control accuracy while avoiding the increased device complexity that would result from adding a reset circuit.
Data Source
AI summary
An electronic circuit includes a transimpedance amplifier, a bypass circuit that allows a part of an input signal to be applied to the transimpedance amplifier to flow through the bypass circuit so as to bypass the transimpedance amplifier on the basis of a control signal, and a control signal circuit that includes a hold circuit having a time constant that is variable on the basis of a time constant control signal and generates the control signal.