Solid-State Image Sensor With Pixel Memory Capacitors
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Solution Overview
Problem
Conventional high-speed imaging devices face challenges with high power consumption, signal-to-noise ratio deterioration, and false signals due to dark charges in in-situ storage image sensors, while CMOS image sensors struggle to maintain high-speed operations with low capacitive load and aperture ratio.
Innovation Solution
A solid-state image sensor with a CMOS structure featuring a separate memory area for each pixel, using capacitors to store photocharges, and a buffer element to manage signal transfer, allowing for independent operation of each pixel and reducing capacitive load, thereby minimizing power consumption and enhancing signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If in-situ storage image sensor is used for high-speed imaging, then imaging speed is improved, but power consumption increases excessively
Solution Approach 1:
The image sensor is divided into independent pixel units, each with its own storage capacitor. This segmentation allows parallel operation of multiple pixels without requiring simultaneous driving of all gate electrodes and signal lines, thereby reducing power consumption while maintaining high imaging speed.
Solution Approach 2:
Storage capacitors are introduced as intermediary elements between photodiodes and readout circuits. These capacitors temporarily hold photocharges, enabling decoupling of the photoelectric conversion process from the readout process, which reduces the capacitive load on signal lines and lowers power consumption during high-speed imaging.
2Speed
If in-situ storage image sensor is used for high-speed imaging, then imaging speed is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The storage function is extracted from the readout circuit and placed directly at the pixel level using storage capacitors. This extraction prevents false signals from dark charges in the readout circuit from mixing with photocharges, thereby maintaining signal-to-noise ratio during high-speed imaging operations.
Solution Approach 2:
Storage capacitors serve as intermediary elements that isolate photocharges from dark charges. By holding photocharges locally in capacitors immediately after photoelectric conversion, the system prevents contamination from dark charges generated in subsequent processing stages, preserving signal-to-noise ratio.
3Duration of action of moving object
If storage CCD is provided for each photodiode, then continuous imaging capability is improved, but device complexity increases
Solution Approach 1:
Instead of using a complex storage CCD for each photodiode, the invention segments the storage function into simple capacitors at each pixel. This segmentation dramatically reduces device complexity while maintaining the capability to hold multiple frames of images for continuous high-speed imaging.
Solution Approach 2:
The invention replaces complex, expensive storage CCD structures with simple, inexpensive capacitors that can be easily integrated at the pixel level. These simple capacitors suffice for the temporary storage needed in high-speed imaging, eliminating the need for complex sequential transfer mechanisms.
4Duration of action of moving object
If memory capacitors are increased to record more frames, then continuous recording capability is improved, but capacitive load increases making high-speed operation difficult
Solution Approach 1:
The storage capacity is segmented across multiple independent pixels rather than concentrated in a single high-capacitance memory structure. Each pixel's storage capacitor has small individual capacitance, but collectively they provide sufficient storage for multiple frames, maintaining low capacitive load on signal lines while enabling continuous recording of many frames.
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 high-speed continuous imaging with low power consumption, improved signal-to-noise ratio, and increased dynamic range, allowing for high-quality image capture of rapid phenomena.
Implementation Method 1
pixel signals resulting from photoelectric conversion by the photodiode
Data Source
AI summary
A pixel area with a two-dimensional array of pixels (10) each including a photodiode and a memory area (3a) on which memory sections for holding signals produced by the pixels for continuously recordable frames are separately provided on a semiconductor substrate. All the pixels simultaneously perform a photocharge storage operation, and the signals produced by the photocharge storage are extracted in parallel through mutually independent pixel output lines (14). In a plurality of memory sections connected to one pixel output line, a sample-and-hold transistor of a different memory section is turned on for each exposure cycle so as to sequentially hold signals in a capacitor of each memory section. After the continuous imaging is completed, all the pixel are sequentially read. Unlike CCD cameras, the present sensor does not simultaneously drive all the gate loads. Therefore, the sensor consumes less power yet can be driven at high speeds. The separation between the memory area and pixel area prevents signals from deterioration due to an intrusion of excessive photocharges. As a result, the sensor can perform imaging operations at higher speeds than ever before and yet capture images with higher qualities.