CMOS Image Sensor Wide Dynamic Range Signal Synthesis
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in widening dynamic range, leading to residual images, white defects, and degradation of image quality due to uneven dark-time and KTC noises, as well as difficulties in separating signals of different exposure times.
Innovation Solution
A solid-state image sensing device with a pixel section, AD converting circuit, line memory, control circuit, and synthesizing circuit that processes and compares signals of different exposure times, amplifying and selecting the larger signal to enhance dynamic range without degrading image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complete transfer type photodiodes are used to widen dynamic range, then residual images and white defects are eliminated, but unevenness of dark-time and KTC noises due to leak current in the detecting section degrades image quality
Solution Approach 1:
The patent divides the signal processing into two separate readout paths: one for signal charges read at time t2 (shorter exposure) and another for signal charges read at time t4 (longer exposure). This segmentation allows independent processing of different exposure time signals, enabling the system to eliminate residual images and white defects while managing noise through separate detection channels.
Solution Approach 2:
The patent performs preliminary readout of signal charges at an intermediate time point (t2) before the final readout time (t4). This preliminary action allows the system to capture early signal information and use it in combination with the later readout, thereby eliminating the need for complete transfer that causes residual images and white defects while still achieving wide dynamic range.
2Reliability
If signals of long exposure time and short exposure time are added and output in conventional methods, then dynamic range is widened, but it is difficult to separate the signals of long exposure time and short exposure time from each other
Solution Approach 1:
The patent segments the signal charges into two distinct groups based on their readout timing: those read at time t2 and those read at time t4. By maintaining separate signal paths and using different readout control signals for each group, the system preserves the ability to separately process and analyze signals of different exposure times while still achieving combined dynamic range enhancement.
Solution Approach 2:
The patent introduces an intermediate readout mechanism that acts as a mediator between the photodiode and the final signal processing. By reading signal charges at an intermediate time point (t2) and storing them separately, the system creates an intermediary buffer that allows subsequent separation and independent processing of short and long exposure signals without mixing them together.
3Reliability
If incomplete transfer type photodiodes are used to widen dynamic range, then dynamic range is increased, but residual images and white defects occur and image quality is degraded
Solution Approach 1:
The patent performs a preliminary readout of signal charges at time t2 before the complete transfer and final readout at time t4. This preliminary action captures the signal information early, allowing the system to achieve wide dynamic range through dual readout without requiring incomplete transfer, thereby eliminating residual images and white defects that plague conventional incomplete transfer type photodiodes.
Solution Approach 2:
The patent extracts signal charges from the photodiode at an intermediate time point (t2) before the final readout, rather than waiting for complete transfer. This extraction approach allows the system to obtain signal information without completing the transfer process that causes residual images and white defects, while still achieving the desired dynamic range expansion.
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
Enables the enlargement of dynamic range without lowering image quality by separately processing and amplifying signals of long and short exposure times, improving color reproducibility and linearity of photoelectric conversion characteristics.
Implementation Method 1
each of the cells including photoelectric converting means for converting an optical signal into an electrical signal
Data Source
AI summary
A solid-state image sensor which includes a pixel section, AD converter, line memory, controller and synthesizer is disclosed. The line memory stores a digital signal output from the AD converter. The controller controls the pixel section and AD converter to subject analog signals of different exposure times to an AD converting process by use of the AD converter and transfer the thus AD-converted signals to the line memory in an accumulation period of charges of one frame. The synthesizer is supplied with digital signals of different exposure times from the line memory, compare a fist signal obtained by adding signals of short and long exposure times with a second signal obtained by amplifying the signal of short exposure time by the ratio of the signal of short exposure time to the signal of long exposure time, select a larger one of the compared signals and output the selected signal.