Amplification Transistor Fingers for Solid-State Imaging Noise Reduction
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Solution Overview
Problem
As pixels have become further micronized, it has become difficult to obtain a signal voltage with sufficient voltage value from individual pixels, leading to increased noise components in the output voltage, which deteriorates image quality due to the increased ratio of noise components affecting the output image.
Innovation Solution
A solid-state imaging device comprising a plurality of unit pixels, each with a photoelectric conversion element, a transfer transistor, a charge accumulation unit, an amplification transistor with at least two fingers connected in parallel, and a selection transistor corresponding to each finger, which allows for adjustable conversion efficiency and noise reduction by switching between source follower and differential amplification read-out modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If pixels are micronized to increase resolution, then the number of pixels per unit area increases, but the signal voltage from individual pixels decreases and noise ratio increases
Solution Approach 1:
Multiple fingers of the amplification transistor are connected in parallel to the charge accumulation unit, effectively merging multiple signal paths. This increases the total signal voltage while maintaining the small pixel size, thereby improving the signal-to-noise ratio without sacrificing resolution.
Solution Approach 2:
The amplification transistor is designed with multiple fingers extending in a direction substantially perpendicular to the signal charge transfer direction. This dimensional arrangement allows increased gate width and signal amplification capacity within the constrained pixel area, resolving the contradiction between small pixel size and sufficient signal voltage.
2Measurement precision
If signal detection capacitance is reduced to increase output voltage and sensitivity, then sensitivity improves, but noise components increase and image quality deteriorates
Solution Approach 1:
Multiple fingers are connected in parallel to the charge accumulation unit, which increases the effective signal voltage without requiring reduction of the detection capacitance. This maintains sensitivity while improving the signal-to-noise ratio by increasing the absolute signal level.
Solution Approach 2:
The patent changes the structural parameter of the amplification transistor by increasing the number of fingers and their width, which modifies the electrical characteristics (increased transconductance and signal voltage) without changing the fundamental capacitance values, thereby improving output voltage while maintaining noise performance.
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
The solution effectively reduces noise and improves image quality by increasing the conversion efficiency and dynamic range, while maintaining seamless switching between read-out modes, thus addressing the challenge of micronized pixels and noise-related image deterioration.
Implementation Method 1
a photoelectric conversion element configured to generate an electric charge corresponding to an incident light quantity
Data Source
AI summary
To suppress deterioration of image quality. A solid-state imaging device (1) according to an embodiment includes a plurality of unit pixels (100) each of which includes a photoelectric conversion element (PD) configured to generate an electric charge corresponding to an incident light quantity, a transfer transistor (102) configured to transfer the electric charge generated in the photoelectric conversion element, a charge accumulation unit (FD) configured to accumulate the electric charge transferred by the transfer transistor, an amplification transistor (1051, 1052) including at least two fingers that are connected to the charge accumulation unit in parallel, and a selection transistor (106) that is disposed corresponding to each of the fingers of the amplification transistor on a one-to-one basis.