Low-Light Image Sensor Circuit With Segmented Photodiode Biasing
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Solution Overview
Problem
Active pixel sensors face inefficiencies in low-light environments due to increased parasitic capacitance from larger photodiode areas, leading to reduced image quality.
Innovation Solution
The electronic device incorporates a sensing circuit with a photodiode, transistors, and a capacitor connected in series to limit equivalent capacitance, enhancing reverse bias current and output voltage for improved image detection in low-light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the photodiode area is increased to increase photocurrent in low-light environment, then the photocurrent magnitude is improved, but the parasitic capacitance increases leading to reduced voltage variation and lower image quality
Solution Approach 1:
The photodiode area is divided into a first area and a second area, where the first area generates signal current and the second area generates reference current. This segmentation allows the total photodiode area to be increased for better low-light performance while the reference current compensates for parasitic capacitance effects, maintaining voltage variation and image quality.
2Illumination intensity
If the photodiode area is increased to increase photocurrent, then the light detection capability is improved, but the voltage variation generated by photodiode current is reduced due to increased parasitic capacitance
Solution Approach 1:
A reference current is introduced as an intermediary element that compensates for the reduced voltage variation caused by increased parasitic capacitance. The reference current, generated by a second photodiode area, is subtracted from the signal current to recover the voltage variation needed for high-quality image detection while maintaining large photodiode area for light detection capability.
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 enhances image quality in low-light environments by increasing the reverse bias current and output voltage, reducing the impact of parasitic capacitance without compromising image detection efficiency.
Implementation Method 1
The active pixel sensor employs a photodiode to detect light intensity and convert the same into a current having a magnitude corresponding to the light intensity
Implementation Method 2
The electronic device incorporates a sensing circuit with a photodiode, transistors, and a capacitor connected in series to limit equivalent capacitance, enhancing reverse bias current and output voltage
Data Source
AI summary
An electronic device includes a first transistor, a second transistor, and a sensing circuit coupled to at least one of the first transistor and the second transistor. The sensing circuit includes a diode, a third transistor, and a fourth transistor. The diode has a first terminal. The third transistor has a first terminal and a second terminal. The first terminal of the third transistor is coupled to the first terminal of the diode. The fourth transistor has a first terminal coupled to the second terminal of the third transistor, and a second terminal coupled to a data driver.