Solid-State Imaging Device Charge Segmentation for Dynamic Range
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Solution Overview
Problem
Existing solid-state imaging devices face challenges in accurately reading out signal charges while expanding the dynamic range of output signals, as some signal charges are reset during the floating diffusion capacitor reset process, leading to decreased accuracy.
Innovation Solution
A method and device configuration that utilize a first capacitor to hold part of the signal charges and a combined capacitor of the first and second capacitors to hold the remaining charges, allowing for separate output signals and improved charge handling during exposure and reset periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the floating diffusion capacitor is reset after charge accumulation, then the capacitor can be reused for the next measurement, but some signal charges are accidentally reset along with noise charges, decreasing reading accuracy
Solution Approach 1:
The patent segments the charge holding function into two separate capacitors: the floating diffusion capacitor (first capacitor) and the charge holding portion (second capacitor). Signal charges are transferred to the second capacitor for storage, while the first capacitor is reset separately. This segmentation allows the first capacitor to be reused without losing signal charges, resolving the contradiction between productivity and measurement precision.
2Adaptability or versatility
If a separate charge holding portion is added to expand dynamic range, then overflowed signal charges can be accumulated, but the device complexity increases
Solution Approach 1:
The patent merges the charge holding function with the pixel structure by utilizing the diffusion region that naturally forms during the photoelectric conversion process. The charge holding portion is created by extending the n-type diffusion region, which integrates the holding function into the existing pixel architecture rather than adding a completely separate structure, thereby reducing overall device complexity while expanding dynamic range.
3Measurement precision
If correlated double sampling is performed to reduce noise, then noise components can be decreased, but the reading process becomes more complex and time-consuming
Solution Approach 1:
The patent performs preliminary charge transfer to the charge holding portion before the reset operation. By transferring signal charges to the second capacitor in advance and then resetting the first capacitor, the system eliminates the need for complex correlated double sampling procedures. The preliminary charge separation simplifies the reading process while maintaining high signal accuracy.
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 high-accuracy reading of signal charges and expands the dynamic range of output signals by effectively managing charge transfer and reset operations, reducing noise components and maintaining a high signal-to-noise ratio across varying light conditions.
Implementation Method 1
a photoelectric conversion element that generates signal charges by photoelectric conversion
Data Source
AI summary
A solid-state imaging device includes a pixel that includes a photoelectric conversion element that generates signal charges by photoelectric conversion, a first capacitor, a second capacitor, and an amplifier transistor. At least a part of charges of the signal charges generated by the photoelectric conversion element are held by the first capacitor and are not held by the second capacitor. The amplifier transistor outputs a first signal based on the part of the charges that the first capacitor holds. The part of the charges of the first capacitor are reset, and a combined capacitor of the first capacitor and second capacitor holds other part of charges of the signal charges generated by the photoelectric conversion element. The amplifier transistor outputs a second signal based on the other part of the charges that the combined capacitor holds.