Imaging Device Input Node Capacitance Control for Noise Reduction
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Solution Overview
Problem
Existing imaging devices face noise issues due to inappropriate timing relationships between the reset transistor and FD connection transistor, leading to inaccurate voltage resetting and potential shading effects, especially when switching between modes of operation.
Innovation Solution
The imaging device incorporates a capacitance control unit that switches the capacitance of the input node between two values, allowing for controlled reset operations and noise reduction by managing the capacitance during signal output and reset processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reset transistor is turned on to reset the voltage of the input node, then the voltage resetting function is achieved, but noise and shading effects occur due to inappropriate timing with the FD connection transistor
Solution Approach 1:
The patent applies preliminary action by switching the FD connection transistor off before turning on the reset transistor. This preliminary disconnection of the FD connection transistor prevents the harmful interaction between the reset operation and the floating diffusion regions, thereby eliminating noise and shading effects while maintaining accurate voltage resetting.
2Adaptability or versatility
If the FD connection transistor connects multiple FD regions to change capacitance value, then gain adjustment is achieved, but voltage instability and noise occur during mode switching
Solution Approach 1:
The patent applies preliminary action by disconnecting the FD connection transistor before performing reset operations during mode switching. This ensures that the reset operation affects only the selected pixel's FD region without causing voltage instability or noise from unintended coupling with other FD regions, thereby maintaining voltage stability while preserving gain adjustment capability.
3Reliability
If the reset operation is performed with the FD connection transistor on, then reset function is achieved, but leakage currents increase causing shading effects
Solution Approach 1:
The patent applies preliminary action by turning off the FD connection transistor before activating the reset transistor. This preliminary disconnection isolates the floating diffusion regions, preventing leakage currents from flowing between connected regions during the reset operation, thereby eliminating shading effects while maintaining the reset function.
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 solution effectively reduces noise and improves image quality by stabilizing voltage variations during reset operations, minimizing leakage currents and shading effects across different pixel columns.
Implementation Method 1
a photoelectric conversion portion configured to generate electric charge in accordance with light
Data Source
AI summary
A photoelectric conversion device includes a plurality of pixels. Each pixel includes an amplification transistor that has an input node configured to receive electric charge generated through photoelectric conversion, a reset transistor, and a capacitance control unit. In a state where the reset transistor is off, the capacitance control unit switches a capacitance of the input node from a first capacitance value to a second capacitance value, which is greater than the first capacitance value. Subsequently, the reset transistor is controlled from off to on in a state where the capacitance of the input node has been controlled to the second capacitance value. After the reset operation, the amplification transistor outputs a pixel signal in a state where the capacitance of the input node is the first capacitance value.