CMOS Image Sensor Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
CMOS image sensors face challenges in achieving high-quality imaging data with uniform electrical characteristics of transistors, low power consumption, high-speed operation, high sensitivity, wide dynamic range, and high resolution, while also compensating for variation in threshold voltage and manufacturing complexity.
Innovation Solution
The imaging device incorporates a photoelectric conversion element and multiple transistors, including oxide semiconductors, with specific connections and a compensation method to stabilize threshold voltage, utilizing a capacitor for data retention and dynamic range expansion, and employing a global shutter system for simultaneous imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If data is written to a capacitor by each imaging to compensate for transistor variation, then imaging quality is improved, but total imaging time increases and power consumption increases
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation once during the manufacturing process using a compensation transistor and capacitor, rather than writing compensation data to memory capacitors for each imaging operation. This preliminary compensation establishes uniform electrical characteristics across all pixels before actual imaging begins, eliminating the need for repeated compensation operations and thus reducing total imaging time while maintaining high imaging quality
2Measurement precision
If data is written to a capacitor by each imaging to compensate for transistor variation, then imaging quality is improved, but power consumption increases
Solution Approach 1:
The patent performs threshold voltage compensation once during manufacturing using a compensation transistor and capacitor connected to each pixel's amplifier transistor gate. This preliminary action establishes uniform electrical characteristics before imaging operations begin, eliminating the need for repeated compensation writes to memory capacitors during each imaging cycle, thus significantly reducing power consumption while maintaining high imaging quality
3Manufacturing precision
If miniaturization is pursued to increase resolution, then device density is improved, but manufacturing precision becomes more difficult and transistor electrical characteristic variation increases
Solution Approach 1:
The patent introduces a compensation transistor and capacitor as intermediary elements in each pixel circuit. The compensation transistor is connected between the amplifier transistor gate and a reference potential, with a compensation capacitor storing the compensation voltage. This intermediary mechanism allows precise control and uniformity of amplifier transistor threshold voltages across all pixels, compensating for manufacturing variations that occur during miniaturization and enabling high device density while maintaining electrical characteristic uniformity
Solution Approach 2:
The patent changes the electrical parameters of the amplifier transistor by introducing a compensation voltage through the compensation transistor and capacitor. By adjusting the gate voltage of the amplifier transistor using this compensation mechanism, the patent can uniformize the threshold voltages across all pixels despite miniaturization-induced manufacturing variations, thus maintaining consistent electrical characteristics while achieving high device density
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 enables high-quality imaging data with reduced power consumption, high sensitivity, and a wide dynamic range, while compensating for transistor variation, and is suitable for low-cost, high-reliability, and high-resolution imaging applications.
Implementation Method 1
a photoelectric conversion element
Data Source
AI summary
An imaging device capable of obtaining high-quality imaging data is provided. The imaging device includes a photoelectric conversion element, a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, and a first capacitor. Variation in the threshold voltage of amplifier transistors can be compensated. Furthermore, the imaging device can have a difference detecting function for holding differential data between imaging data for an initial frame and imaging data for a current frame and outputting a signal corresponding to the differential data.