Feedback Transimpedance Amplifier for Stable Input Termination
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Solution Overview
Problem
Transimpedance amplifiers (TIAs) with high input resistance values exhibit significant manufacturing variations, leading to fluctuations in input resistance and frequency characteristics, which can result in incorrect termination and performance issues in LiDAR and optical communication systems.
Innovation Solution
A transimpedance amplifier configuration that includes an input terminal, a first transistor, current-voltage and voltage-current conversion circuits, an inverting amplifier circuit, and feedback loops to reduce input resistance and stabilize frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the input resistance value of the TIA is made large, then the sensitivity of the photodetection device is improved, but the fluctuation range of the input resistance value due to manufacturing variations becomes large
Solution Approach 1:
The patent changes the parameter of input resistance from a large fixed value to a small adjustable value. By reducing the input resistance to 1Ω or less and making it adjustable through control signals, the system achieves both good manufacturing consistency (small values are less sensitive to variations) and maintains photodetection capability through the TIA's high gain configuration.
2Measurement precision
If the input resistance value of the TIA is large, then the photodetection capability is enhanced, but the frequency characteristics fluctuate due to incorrect termination
Solution Approach 1:
The patent changes the input resistance parameter to a small value (1Ω or less) to ensure proper termination and stable frequency characteristics. The photodetection capability is maintained not through high input resistance but through the TIA's high transimpedance gain, separating the termination function from the detection function.
Solution Approach 2:
The patent implements a feedback mechanism where a control signal is generated based on the detected optical signal and fed back to adjust the input resistance. This feedback loop stabilizes the frequency characteristics by dynamically adjusting the termination impedance to match the transmission line, preventing reflections and oscillations.
3Manufacturing precision
If the input resistance value is reduced, then the termination accuracy is improved, but the photodetection sensitivity may be compromised
Solution Approach 1:
The patent decouples the termination function from the detection function by using a small input resistance (1Ω or less) for accurate termination while relying on the TIA's high transimpedance gain for sensitive detection. This parameter separation allows both termination accuracy and detection sensitivity to be optimized independently.
Data Source
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Figure 3A
AI summary
A transimpedance amplifier includes an input terminal, a first transistor having a source connected to the input terminal, a first current-voltage conversion circuit, a first voltage-current conversion circuit and a second voltage-current conversion circuit that convert a voltage corresponding to an output voltage of the first current-voltage conversion circuit into a current, an inverting amplifier circuit having an input node connected to the source or the emitter of the first transistor and an output node connected to a gate or a base of the first transistor, a second current-voltage conversion circuit that converts an output current of the second voltage-current conversion circuit into a voltage, and an output terminal that outputs the voltage converted by the second current-voltage conversion circuit, wherein the output current of the first voltage-current conversion circuit is fed back to the source or the emitter of the first transistor.