CMOS Image Sensor Charge Holding Portion Control
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Solution Overview
Problem
Image pickup sensors, such as CMOS image sensors, face challenges in reducing dark current noise while expanding dynamic range, especially during high-sensitivity photography, leading to degraded image quality due to noise amplification.
Innovation Solution
An image pickup apparatus with a photoelectric conversion element, a charge accumulation portion, and a charge holding portion, where a controller sets operation modes to separate or connect the charge holding and accumulation portions based on photographing conditions, allowing for dynamic range expansion while minimizing dark current noise influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a charge holding portion is provided in each image pickup element to expand dynamic range, then the dynamic range is improved, but dark current noise increases leading to degraded image quality
Solution Approach 1:
The patent applies dynamics by making the connection state between the charge holding portion and charge accumulation portion changeable over time. The second transfer switch selectively connects or separates the charge holding portion from the charge accumulation portion based on photographing conditions, allowing the system to adapt between noise reduction mode (separated) and dynamic range expansion mode (connected), thus resolving the contradiction between these two opposing requirements.
2Quantity of substance
If the second transfer switch connects the charge holding portion and charge accumulation portion during charge accumulation, then dynamic range is expanded, but dark current noise in the charge holding portion is accumulated
Solution Approach 1:
The patent dynamically controls the state of the second transfer switch based on photographing conditions. When high-sensitivity photography is detected, the switch separates the charge holding portion from the charge accumulation portion during charge accumulation, preventing dark current noise accumulation while still allowing dynamic range expansion when needed. This temporal separation resolves the contradiction between dynamic range expansion and noise accumulation.
3Measurement precision
If high-sensitivity photography is performed with charge accumulation in the charge holding portion, then ISO sensitivity is improved, but noise amplification degrades image quality
Solution Approach 1:
The patent dynamically adjusts the connection state of the second transfer switch based on detected photographing conditions. When high-sensitivity photography is detected, the system separates the charge holding portion from the charge accumulation portion during charge accumulation, preventing dark current noise accumulation that would otherwise be amplified during high-sensitivity processing. This resolves the contradiction between achieving high ISO sensitivity and avoiding noise amplification.
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 approach enables excellent image quality by prioritizing dynamic range expansion when needed and noise reduction when sufficient, depending on the photographing conditions, effectively managing dark current noise in high-sensitivity scenarios.
Implementation Method 1
a photoelectric conversion element configured to generate and accumulate electric charge in response to an optical input
Data Source
AI summary
An image pickup apparatus capable of reducing the influence of dark current noise to thereby obtain excellent image quality, even when the dynamic range is expanded under a photographing condition. In an image pickup element of a CMOS image sensor of the apparatus, a photo diode (PD) generates and accumulates electric charge according to an optical input, and a floating diffusion portion (FD) accumulates the electric charges. A charge holding portion (MEM) is disposed between PD and FD. A first transfer transistor selectively separates and connect between PD and MEM, and a second transfer transistor selectively separates and connects between MEM and FD. A system control circuit sets an operation mode to either a first operation mode in which PD and MEM are separated or a second operation mode according to photographing conditions for shooting an object in which PD and MEM are connected.