Solid-State Image Sensor Charge Limiting for Pseudo-Smear Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing solid-state image sensors face challenges in effectively reducing pseudo-smear, a defect caused by charge overflow, due to complex configurations and operations, and existing solutions either complicate the setup or lead to image degradation.
Innovation Solution
A solid-state image sensor design that limits the upper limit amount of charges transferred to the floating diffusion unit, using a set gain for A/D conversion and intermediate voltage generation to control transistor states, thereby reducing charge overflow and pseudo-smear occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the upper limit amount of charges retained in the floating diffusion area is decreased to reduce pseudo-smear, then the occurrence of pseudo-smear is reduced, but the dynamic range for A/D conversion is reduced
Solution Approach 1:
The patent divides the charge transfer path into two segments: first from the photodiode to the floating diffusion area, and second from the floating diffusion area to the hold unit. This segmentation allows independent control of charge amounts at different stages, enabling the floating diffusion area to maintain a limited charge amount (reducing pseudo-smear) while the hold unit accumulates sufficient charges for A/D conversion.
Solution Approach 2:
The hold unit acts as an intermediary between the floating diffusion area and the A/D conversion unit. It temporarily stores charges and allows accumulation of sufficient charge amounts for A/D conversion without affecting the charge limit in the floating diffusion area. This mediator resolves the contradiction by decoupling the charge amount constraints between the two regions.
2Object-affected harmful factors
If a complex configuration is used to reduce pseudo-smear (such as separate detection circuits or clipping circuits), then pseudo-smear reduction is achieved, but the device complexity increases
Solution Approach 1:
The hold unit serves multiple functions: it acts as a charge storage region, a charge accumulation buffer for A/D conversion, and a pseudo-smear prevention mechanism. By making this single component multi-functional, the patent avoids the need for separate detection circuits, clipping circuits, or other complex configurations that would increase device complexity.
Solution Approach 2:
The pixel circuit structure itself, particularly the hold unit and the controlled charge transfer mechanism, automatically prevents pseudo-smear without requiring external detection or correction circuits. The system uses its own internal structure and operation to solve the pseudo-smear problem, eliminating the need for additional complex components.
3Productivity
If strong light is incident on pixel circuits, then photoelectric conversion efficiency is high, but charge overflow occurs causing pseudo-smear in other pixel circuits of the same control group
Solution Approach 1:
The patent establishes a predetermined upper limit for the charge amount in the floating diffusion area before charge overflow can occur. By controlling the transfer of charges from the photodiode to the floating diffusion area and then to the hold unit, the system prevents excessive charge accumulation that would cause pseudo-smear in neighboring pixel circuits, while still allowing efficient photoelectric conversion during strong light conditions.
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 effectively reduces pseudo-smear by limiting charge fluctuations within pixel circuit units, simplifying the configuration and operation while maintaining image quality.
Implementation Method 1
a photodiode PD that generates charges via photoelectric conversion
Data Source
AI summary
Provided are a solid-state image sensor and an electronic information device capable of effectively reducing the occurrence of pseudo-smear by adopting a simple configuration and operation. A solid-state image sensor 1 includes multiple pixel circuit units PN and POB, each including a photoelectric conversion unit that generates charges via photoelectric conversion and accumulates the generated charges, a floating diffusion unit that retains charges transferred from the photoelectric conversion unit, a transfer unit through which charges accumulated by the photoelectric conversion unit are transferred to the floating diffusion unit, an output unit that outputs a signal corresponding to the amount of charges retained by the floating diffusion unit, and a reset unit that discharges charges retained by the floating diffusion unit to the outside; and an A/D conversion unit 23 that acquires a signal output from the output unit and performs A/D conversion on the acquired signal using a set gain. At least one of the pixel circuit units PN and POB is configured such that charges transferred from the photoelectric conversion unit to the floating diffusion unit and retained by the floating diffusion unit are limited so as not to exceed an upper limit amount which is set to be smaller by the extent of an increase in the gain.