Photodetector Circuit Stabilization via Capacitor Charge Storage
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Solution Overview
Problem
Conventional photodetector circuits experience changes in circuit characteristics due to time degradation of MOS transistors, leading to inaccuracies in light detection.
Innovation Solution
A photodetector circuit design that includes a photodetector transistor, a current output transistor, a switching transistor, and a capacitor, where the source of the photodetector transistor, the gate of the current output transistor, and a terminal of the capacitor are connected, allowing for the storage of electric charges and setting the potential difference to the threshold voltage of the current output transistor, reducing the impact of transistor characteristic variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MOS transistors are used in photodetector circuits, then the circuit can operate with standard transistor components, but the circuit characteristics change over time due to transistor degradation
Solution Approach 1:
The patent applies preliminary action by pre-setting the gate-source voltage of the current output transistor to its threshold voltage using a capacitor during an initialization phase. This preliminary voltage setting compensates for subsequent transistor degradation, maintaining circuit characteristics stable over extended operational periods without requiring continuous adjustment.
2Reliability
If the threshold voltage of the current output transistor varies due to degradation, then transistor aging is naturally accounted for, but the circuit characteristics become influenced by such variations
Solution Approach 1:
The patent utilizes parameter changes by dynamically adjusting the gate-source voltage parameter of the current output transistor. A capacitor stores and applies a voltage that shifts the transistor's operating point to compensate for threshold voltage drift, thereby maintaining detection accuracy despite aging effects.
3Reliability
If additional components like capacitors are added to compensate for transistor degradation, then circuit characteristic stability improves, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the capacitor to serve multiple functions: it acts as a charge storage element for the photodetector signal, a voltage reference source for the current output transistor, and a compensation mechanism for threshold voltage drift. This multi-functionality reduces the need for separate dedicated components.
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
This design stabilizes the circuit characteristics by storing electric charges in a capacitor, allowing the photodetector circuit to maintain accurate light detection even with variations in transistor threshold voltages, reducing the need for separate detection of threshold voltage variations and minimizing the occupation period of photodetector circuits on detection lines.
Implementation Method 1
the source of the photodetector transistor collects electric charges generated by an internal photoelectric effect
Implementation Method 2
the potential difference between the gate and the source of the current output transistor can be set to a present threshold voltage of the current output transistor by storing the electric charges in the first capacitor
Data Source
AI summary
A photodetector circuit includes: a photodetector transistor; a current output transistor; a switching transistor; and a first capacitor. The source of the photodetector transistor, the gate of the current output transistor, and the first terminal of the first capacitor are connected to one another. The source of the current output transistor, the drain of the switching transistor, and the second terminal of the first capacitor are connected to one another. The photodetector transistor has a drain connected to a reference potential line, and upon receiving light when the photodetector transistor is in an off state, the source of the photodetector transistor collects electric charges generated by an internal photoelectric effect. The current output transistor has a drain connected to a power line which can have a first power supply potential and a second power supply potential. The switching transistor has a source connected to a photodetection line.