CMOS Pixel Readout Circuit Threshold Compensation
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Solution Overview
Problem
Conventional CMOS image sensors require a double readout operation to compensate for threshold voltage differences between drive transistors, leading to increased power consumption, reduced data conversion time, and deteriorated noise characteristics, making it difficult to achieve high-resolution imaging.
Innovation Solution
A pixel signal readout device with a column select transistor is introduced to compensate for threshold voltage differences, allowing for a single readout operation by initializing pixel signal loading lines using a reference voltage and performing a diode connection with the drive transistor to extract and compensate for the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a double readout operation is performed to compensate for threshold voltage differences, then measurement precision is improved, but productivity deteriorates
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation during the pixel signal readout process itself, rather than requiring a separate preliminary readout operation. The column selection transistor is configured to automatically compensate for threshold voltage differences as the pixel signal is being read out, eliminating the need for a separate CDS readout operation and thereby maintaining both measurement precision and productivity
2Measurement precision
If a double readout operation is performed to compensate for threshold voltage differences, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The patent performs threshold voltage compensation during the normal pixel signal readout operation, eliminating the need for a separate preliminary readout operation. This integration reduces the total number of readout operations from two to one, thereby reducing power consumption while maintaining measurement precision through the column selection transistor's automatic compensation mechanism
3Measurement precision
If a double readout operation is performed to compensate for threshold voltage differences, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent performs threshold voltage compensation during the pixel signal readout process itself, rather than requiring a separate preliminary readout operation. The column selection transistor is configured to automatically compensate for threshold voltage differences as the pixel signal is being read out, eliminating the need for a separate CDS readout operation and thereby reducing data conversion time while maintaining measurement precision
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 readout time, decreases power consumption, and improves noise characteristics, enabling the realization of high-resolution CMOS image sensors.
Implementation Method 1
performing photoelectric conversion by the photodetector
Data Source
AI summary
A pixel signal readout device includes a unit pixel including a drive transistor and a reset transistor; and a column select transistor suitable for outputting a voltage applied to one terminal thereof, to a common terminal of the drive transistor and the reset transistor through the other terminal thereof, in response to a column select control signal applied to a gate terminal thereof.