CMOS Unit Pixel Threshold Voltage Compensation via Correlated Dual Sampling
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Solution Overview
Problem
Conventional CMOS image sensors face increased power consumption and reduced data conversion time due to the need for two readout operations to compensate for threshold voltage differences in drive transistors caused by manufacturing process variations, leading to deteriorated noise characteristics and difficulty in implementing high-resolution imaging.
Innovation Solution
A unit pixel structure and operating method that compensates for threshold voltage differences by adjusting control timing and pixel structure, allowing for accurate pixel signal readout through a single readout operation, involving a photo sensitive device, reset transistor, selection transistors, and a drive transistor forming a diode connection to extract and compensate threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If two readout operations are performed to compensate for threshold voltage differences, then manufacturing process variations are addressed, but power consumption increases and readout time increases
Solution Approach 1:
The patent applies preliminary action by performing the threshold voltage compensation during the integration period before the actual pixel signal readout. The first readout operation (reset signal readout) is executed in advance to establish the offset value, which is then subtracted from the second readout operation (pixel signal readout). This preliminary compensation action eliminates the need for separate compensation steps, reducing total readout time and power consumption while maintaining manufacturing process variation compensation.
2Manufacturing precision
If two readout operations are performed to compensate for threshold voltage differences, then manufacturing process variations are addressed, but data conversion time is reduced
Solution Approach 1:
The patent merges the threshold voltage compensation function with the pixel signal readout operation. Instead of performing separate compensation and readout operations, the method combines both functions into a single correlated dual sampling process where the reset signal readout and pixel signal readout are integrated into one continuous operation sequence. This merging reduces the total number of discrete operations and minimizes readout time while maintaining compensation accuracy.
3Manufacturing precision
If two readout operations are performed to compensate for threshold voltage differences, then manufacturing process variations are addressed, but noise characteristic is deteriorated
Solution Approach 1:
The patent applies feedback by using the reset signal readout value as a reference to compensate for threshold voltage offsets in the pixel signal readout. The offset value obtained from the first readout operation is fed back and subtracted from the second readout operation, creating a correlated dual sampling process. This feedback mechanism effectively removes fixed-pattern noise and thermal noise components, improving noise characteristics while maintaining manufacturing process variation compensation.
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 reduces power consumption and improves noise characteristics by minimizing readout time, enabling the implementation of high-resolution CMOS image sensors.
Implementation Method 1
The photo sensitive device may generate photo charges corresponding to incident light
Data Source
AI summary
This technology relates a unit pixel and an operating method thereof and a CMOS image sensor using the same. The unit pixel may include a photo sensitive device; a reset transistor; a selection transistor including a gate terminal, a first terminal and a second terminal, suitable for operating in response to a selection control signal applied to the gate terminal and outputting a voltage applied to the first terminal to a first terminal of the reset transistor through the second terminal; and a drive transistor including a first terminal coupled to the second terminal of the selection transistor, a second terminal and a gate terminal, suitable for generating an electrical signal corresponding to charges accumulated in a floating diffusion node coupled to the gate terminal, and outputting the electrical signal as a pixel signal through the second terminal.