Solid-State Image Sensor Differential Amplification Gain Control
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Solution Overview
Problem
In conventional solid-state imaging elements, the initialization of floating diffusion layers in both read and reference pixels leads to equal potentials for the drain and gate of the amplification transistor, resulting in increased gain variation and deteriorated image quality.
Innovation Solution
A solid-state imaging element is designed with a reference-side amplification transistor, a read-side amplification transistor, a pair of reset transistors, and a potential difference control circuit that sets the potential difference between the gate and drain of the amplification transistor to a predetermined value during initialization, reducing gain variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate and drain of the amplification transistor are short-circuited during initialization, then the floating diffusion layers are initialized, but the gain variation of the amplification transistor increases
Solution Approach 1:
The patent separates the initialization control for gate and drain by introducing independent reset transistors (first reset transistor for gate, second reset transistor for drain) instead of a single short-circuit connection. This segmentation allows different potential control strategies for each terminal during initialization.
Solution Approach 2:
The patent changes the potential parameter relationship between gate and drain by maintaining a predetermined potential difference (Vgs) during initialization instead of forcing them to be equal. The potential difference control circuit ensures Vgate - Vdrain = predetermined value, preventing the gain variation caused by equal potentials.
2Manufacturing precision
If a potential difference control circuit is added to maintain predetermined potential difference, then the gain variation is reduced, but the device complexity increases
Solution Approach 1:
The potential difference control circuit uses the existing amplification transistor's own characteristics (gate-source voltage relationship) to maintain the potential difference. The circuit leverages the natural Vgs relationship of the amplification transistor rather than requiring external complex control mechanisms.
Solution Approach 2:
The first reset transistor serves dual functions: it acts as a reset switch for the gate and simultaneously as part of the potential difference control mechanism. This multi-functionality reduces the need for additional dedicated components.
Data Source
AI summary
To improve an image quality in a solid-state imaging element that performs differential amplification. A reference-side amplification transistor supplies a reference current corresponding to a predetermined reference potential. A read-side amplification transistor supplies a signal current corresponding to a difference between a potential of a gate and the reference potential from a drain to a source. A pair of reset transistors initializes the potential of the gate and the reference potential. A potential control circuit controls a potential difference between the gate and the drain to a predetermined value when the potential of the gate and the reference potential are initialized.