Imaging Device Charge Accumulation Dynamic Range
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Solution Overview
Problem
Existing imaging devices face challenges in expanding the dynamic range due to limitations in the amount of electric charges that can be stored in the second photoelectric conversion element, which is not adequately increased beyond the area ratio compared to the first photoelectric conversion element.
Innovation Solution
The imaging device incorporates a first photoelectric conversion unit with higher sensitivity and a second photoelectric conversion unit with lower charge conversion per unit time, along with a charge accumulation unit, charge voltage conversion unit, transfer gate units, and an overflow path to transfer excess charges, and a light reducing unit to manage light entry, enabling effective charge accumulation and expanded dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a second photoelectric conversion element with lower sensitivity is provided to expand dynamic range, then the illuminance range is improved, but the amount of electric charge that can be stored is limited by the area ratio between the first and second photoelectric conversion elements
Solution Approach 1:
The patent introduces a temporal dimension to charge storage by implementing a charge accumulation unit that stores electric charges over time. The second photoelectric conversion element transfers charges to the accumulation unit across multiple cycles, effectively increasing storage capacity beyond the spatial area ratio. This is achieved through controlled transfer timing where charges are accumulated gradually rather than being limited by the instantaneous area of the photoelectric conversion elements.
Solution Approach 2:
The charge accumulation unit acts as an intermediary between the second photoelectric conversion element and the final readout circuit. This intermediate storage mechanism allows charges to be accumulated over multiple conversion cycles, decoupling the storage capacity from the area ratio of the photoelectric conversion elements. The accumulation unit mediates the transfer process, enabling extended dynamic range by storing charges that would otherwise be limited by the small area of the second photoelectric conversion element.
2Adaptability or versatility
If the second photoelectric conversion element stores more electric charges, then the dynamic range is expanded, but the saturation point is reached more easily under high illuminance conditions
Solution Approach 1:
The patent implements dynamic control of the charge transfer process through controlled transfer timing. The transfer of charges from the second photoelectric conversion element to the accumulation unit is regulated to occur at specific timing intervals, allowing the system to adapt to varying illuminance conditions. This dynamic transfer mechanism prevents saturation by controlling when charges are moved, enabling the system to maintain reliability across different lighting conditions while still expanding the overall dynamic range.
3Quantity of substance
If the area of the second photoelectric conversion element is increased to store more charges, then the charge accumulation capacity is improved, but the pixel area and device complexity increase
Solution Approach 1:
The patent resolves the area constraint by transitioning from spatial to temporal charge accumulation. Instead of increasing the area of the second photoelectric conversion element, the system uses the time dimension to accumulate charges across multiple conversion cycles. The charge accumulation unit stores charges temporarily, allowing small-area photoelectric conversion elements to achieve effective large-area charge storage capability through multi-cycle accumulation and controlled transfer timing.
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 configuration allows for a further expansion of the dynamic range, enabling the capture of images with both high sensitivity and a wide dynamic range by effectively managing charge accumulation and light reduction.
Implementation Method 1
a first photoelectric conversion unit (101), a second photoelectric conversion unit (102) having a smaller electric charge amount to be converted per unit time than the first photoelectric conversion unit
Data Source
AI summary
Provided are a first photoelectric conversion unit, a second photoelectric conversion unit having a smaller electric charge amount to be converted per unit time than the first photoelectric conversion unit, a charge accumulation unit that accumulates an electric charge generated by the second photoelectric conversion unit, a charge voltage conversion unit, a first transfer gate unit that transfers an electric charge from the first photoelectric conversion unit to the charge voltage conversion unit, a second transfer gate unit that couples potentials of the charge voltage conversion unit and the charge accumulation unit, a third transfer gate unit that transfers an electric charge from the second photoelectric conversion unit to the charge accumulation unit, an overflow path formed under a gate electrode of the third transfer gate unit and transfers an electric charge overflowing from the second photoelectric conversion unit to the charge accumulation unit, and a light reducing unit that reduces light to enter the second photoelectric conversion unit.