Solid-state imaging element circuit stability via gate-source capacitance
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Solution Overview
Problem
The conventional asynchronous type solid-state imaging elements experience instability in their current-voltage conversion circuits due to potential oscillation, affecting the accuracy of light detection.
Innovation Solution
Incorporating a capacitance between the gate and source of the conversion transistor, along with a current source transistor and a voltage supply transistor, to compensate for phase delays in the output signal, and arranging these components on separate or shared wiring layers to enhance circuit stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If two N-type transistors are connected in a looped pattern in the current-voltage conversion circuit, then the circuit can operate as an asynchronous type solid-state imaging element with real-time event detection capability, but the circuit may become unstable and oscillate under certain conditions
Solution Approach 1:
A capacitance element is introduced as an intermediary component between the two N-type transistors in the looped configuration. This capacitance acts as a mediator that dampens oscillations and stabilizes the circuit while preserving the asynchronous event detection functionality. The capacitance absorbs voltage fluctuations that would otherwise cause instability in the looped transistor configuration.
Solution Approach 2:
The circuit configuration is modified by adding a capacitance element that changes the electrical parameters of the looped transistor circuit. This addition alters the impedance and time constants of the circuit, preventing oscillation conditions while maintaining the real-time detection capability. The capacitance value is selected to optimize both stability and response speed.
2Reliability
If a capacitance is added between the gate and source of the conversion transistor to compensate for phase delay, then circuit stability increases, but the device complexity increases
Solution Approach 1:
The capacitance element is integrated into the existing circuit topology by connecting it between the gate and source terminals of the conversion transistor. This merging approach incorporates the phase compensation function directly into the transistor structure without requiring separate compensation circuits, thereby minimizing the increase in device complexity while achieving improved stability.
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 configuration significantly increases the stability of the current-voltage conversion circuit, reducing the likelihood of oscillation and improving the accuracy of light detection in solid-state imaging elements.
Implementation Method 1
a photodiode that photoelectrically converts incident light and generates photocurrent
Data Source
AI summary
Stability of a current-voltage conversion circuit is increased in a solid-state imaging element that converts photocurrent to a voltage signal.A photodiode photoelectrically converts incident light and generates photocurrent. A conversion transistor converts photocurrent to a voltage signal and outputs the voltage signal from a gate. A current source transistor supplies predetermined constant current to an output signal line connected to the gate. A voltage supply transistor supplies a certain voltage corresponding to the predetermined constant current from the output signal line to a source of the conversion transistor. A capacitance is connected between the gate and the source of the conversion transistor.