CMOS Radiation Sensor Indefinite Potential Control
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Solution Overview
Problem
CMOS image sensors in radiation imaging apparatuses face issues with indefinite potential generation, leading to random noise and incorrect fixed pattern noise (FPN) correction during high-sensitivity mode operation, affecting image quality and frame rate.
Innovation Solution
A radiation imaging apparatus with a control unit that fixes indefinite potentials in the CMOS image sensor by controlling storage and reading operations, utilizing a pixel circuit with reset and sensitivity switching transistors, clamp circuits, and sample and hold units to manage charge and noise signals, allowing for accurate FPN correction and reduced noise components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FPN correction is performed using a fixed pattern noise pattern acquired before moving image capturing, then FPN correction can be applied to moving image data, but the potential at floating portions changes with time causing incorrect correction
Solution Approach 1:
The patent applies preliminary action by acquiring the FPN pattern immediately before moving image capturing rather than at an earlier time. This timing ensures that the potential at floating portions remains stable between FPN pattern acquisition and moving image capture, eliminating the potential drift issue while still allowing FPN correction to be performed. The FPN correction unit uses this timely-acquired pattern to correctly subtract fixed pattern noise from moving image data.
2Measurement precision
If high-sensitivity mode is used in CMOS image sensor, then sensitivity is improved, but indefinite potential is generated causing random noise
Solution Approach 1:
The patent extracts and removes the harmful indefinite potential from the system by introducing a potential fixing unit that actively maintains constant potential at floating portions. This unit specifically targets and eliminates the random noise component generated in high-sensitivity mode without affecting the beneficial sensitivity improvement. The extraction principle separates the harmful potential fluctuation from the useful signal detection capability.
Solution Approach 2:
The patent converts the harmful effect of indefinite potential into a beneficial outcome by using the potential fixing unit to actively stabilize floating portion potentials. Instead of allowing the indefinite potential to cause random noise, the system uses control signals to maintain constant potential, thereby transforming what would be a noise source into a stable reference that enables high-sensitivity operation without degradation from random noise.
3Area of stationary object
If large-area CMOS image sensor is used, then large screen is achieved, but manufacturing precision becomes more difficult
Solution Approach 1:
The patent applies segmentation by dividing the large-area sensor into multiple smaller sensor units that are tiled together to form the complete large-screen sensor. Each individual sensor unit can be manufactured with standard precision, avoiding the microfabrication difficulties that would arise from attempting to manufacture a single large sensor. The segmentation approach allows the system to achieve large screen area while maintaining manufacturing precision through modular construction.
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 enables accurate FPN correction and reduces noise components, allowing for high-frame-rate imaging without influencing operational time, even during changes in frame rate or radiation exposure.
Implementation Method 1
a photodiode PD that converts incident radiation into charge
Data Source
AI summary
A radiation imaging apparatus includes: a radiation detection unit in which a plurality of photoelectric conversion units to convert radiation signals into charge signals and store the charge signals is located; a storage control unit configured to control the storage of the charge signals executed by the plurality of photoelectric conversion units; a reading control unit configured to control reading of the charge signals stored by the plurality of photoelectric conversion units; and a control unit configured to fix an indefinite potential generated at the radiation detection unit while at least one of the storage control of the charge signals by the storage control unit and the reading control of the charge signals by the reading control unit is not carried out.