CMOS Image Sensor Dark Current Cancellation via Reference Pixel
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Solution Overview
Problem
Existing solid-state imaging technologies, particularly CMOS image sensors, face challenges in providing an ample dynamic range due to the amplification of dark current components, which restricts the imaging signal dynamic range, especially at high temperatures and during long exposure times.
Innovation Solution
A solid-state imaging element with a pixel array section and a readout load section, where a reference pixel with similar characteristics to the readout pixel is used to form a differential amplification circuit, and a pseudo-dark current signal is input to the reference pixel to cancel out the dark current signal, thereby enhancing the dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential amplification is used to improve signal conversion efficiency, then signal-to-noise ratio is improved, but dynamic range is reduced due to dark current amplification
Solution Approach 1:
The pixel array is divided into readout pixels and reference pixels, with the reference pixels specifically dedicated to measuring dark current. This segmentation allows independent measurement and subtraction of dark current signals, resolving the contradiction between amplification gain and dynamic range by separating the dark current measurement function from the light signal measurement function.
Solution Approach 2:
Reference pixels serve as an intermediary mechanism to measure and characterize dark current. By using these reference pixels to capture dark current signals under the same conditions, the system can subtract the measured dark current from the readout pixel signals, thereby extending the effective dynamic range while maintaining differential amplification benefits.
2Duration of action of moving object
If dark current amplification occurs during long exposure, then signal accumulation is improved, but dark current noise increases and restricts dynamic range
Solution Approach 1:
The system performs preliminary measurement of dark current signals using reference pixels before they contaminate the light signal measurements. By measuring dark current during the same exposure period in dedicated reference pixels, the system can accurately characterize and subsequently subtract the dark current component, allowing long exposure times without dynamic range restriction.
Solution Approach 2:
The system implements a feedback mechanism where dark current measurements from reference pixels are used to adjust and compensate the readout pixel signals. This real-time dark current characterization and subtraction feedback loop enables the system to maintain accurate dynamic range measurement even during long exposure periods when dark current would otherwise accumulate and restrict the usable signal range.
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 effectively cancels the dark current component, allowing for an ample dynamic range in imaging conditions where dark current is significant, such as high temperatures and long exposure times, by using a pseudo-dark current signal to counteract the dark current signal, thus improving the imaging signal's dynamic range.
Implementation Method 1
a photodiode, a transfer transistor, a reset transistor, a pixel amplifier and a select transistor
Data Source
AI summary
The present technology relates to a solid-state imaging element and an imaging apparatus that provides an ample dynamic range. The solid-state imaging element includes a pixel array section and a readout load section. The pixel array section has a readout pixel and a reference pixel. A pixel signal proportional to an amount of incident light is read out from the readout pixel. The reference pixel has characteristics similar to those of the readout pixel. The readout load section forms a differential amplification circuit together with the readout pixel and the reference pixel and inputs, to the reference pixel, a pseudo-dark current signal corresponding to a dark current signal that occurs in the readout pixel, thus canceling the dark current signal. The present technology is applicable to a CMOS image sensor.