CMOS Image Sensor Multi-Step Gain for Low-Light Dynamic Range
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in low-light conditions due to limited dynamic range, high noise, and power consumption, making them inefficient for applications requiring high-resolution images in low-light environments.
Innovation Solution
The implementation of a high dynamic range CMOS image sensor using a cascade of amplifying steps with MOS capacitor (MOS-CAP) amplification, where two or more pixels work in tandem to provide multi-step gain without significantly increasing pixel area or power consumption, enhancing the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CMOS sensors amplify the input signal using traditional voltage amplifiers, then the signal gain is improved, but the pixel area increases and noise is added to the signal
Solution Approach 1:
The patent merges the photodetector and amplifier into a single integrated pixel structure, where the photodetector directly drives the amplifier without requiring separate large-area voltage amplifier circuits. This integration achieves high signal gain while minimizing pixel area by eliminating the need for bulky discrete amplifier components.
Solution Approach 2:
The patent replaces traditional voltage amplification mechanisms with a current-mode amplification approach using a photodetector directly coupled to a current amplifier. This substitution eliminates the need for high-voltage signal paths and large-area voltage amplifier circuits, reducing pixel area while maintaining high gain capability.
2Measurement precision
If traditional sensors use high voltage amplification to achieve high gain, then the signal amplification is improved, but the power consumption increases
Solution Approach 1:
The patent changes the operating parameters from high-voltage operation to low-voltage current-mode operation. The photodetector generates current signals that are amplified in the current domain, eliminating the need for high-voltage amplification stages and thereby significantly reducing power consumption while achieving high signal amplification.
Solution Approach 2:
The patent substitutes high-voltage voltage amplification with low-voltage current amplification. The photodetector output current is directly amplified by a current amplifier circuit operating at low voltages, replacing the traditional high-voltage path and reducing power consumption while maintaining high gain.
3Measurement precision
If conventional sensors use high voltage amplification, then the signal gain is improved, but the generated noise increases
Solution Approach 1:
The patent replaces high-voltage voltage amplification with low-voltage current-mode amplification. Current-mode operation inherently generates less noise than voltage-mode operation at high voltages, and the direct coupling of the photodetector to the current amplifier minimizes noise introduction while achieving high signal gain.
4Use of energy by moving object
If in-pixel voltage amplifiers are used to provide gain, then the power consumption is reduced, but the pixel area increases significantly
Solution Approach 1:
The patent merges the photodetector and amplifier functions into a tightly integrated pixel structure where the photodetector directly drives the current amplifier. This merger eliminates the need for separate large-area voltage amplifier circuits while maintaining low power consumption through current-mode operation.
Solution Approach 2:
The patent substitutes voltage amplifier circuits with a current amplifier architecture that requires minimal pixel area. The current-mode operation and direct photodetector coupling eliminate the need for bulky voltage amplification stages, achieving both low power consumption and compact pixel area.
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 results in a more efficient, compact, and economical image sensor with improved signal-to-noise ratio and reduced noise performance, enabling high-resolution imaging in low-light conditions without the need for high voltages or bulky hardware.
Implementation Method 1
a photocathode made from GaAs, GaAsP (Gallium Arsenide and Gallium Arsenide Phosphide as substrates) is used for emission of photoelectrons
Implementation Method 2
making use of the MOS capacitor (MOS-CAP) amplification method
Data Source
AI summary
A method and a system are disclosed for pixel-embedded signal amplification of a CMOS image sensor using multi-step voltage-gain enhancement. It involves activating a row of the CMOS image sensor by resetting switches SRST 202, SH1 201 and SH2 209 to charge nodes PD1, PD2, SD1, and SD2 to a pre-set voltage potential and VRST 203. The CMOS sensor switches OFF SRST 202, SH1 201 and SH2 209 for integration of the charges at PD1 for producing a corresponding photo-generated signal. This signal is sampled by transferring to a gate of source follower SF1, to produce an amplified signal. It further involves double-sampling the amplified signal for removing any pixel-offset variation to produce a resultant signal. The said method is repeated for second row of CMOS image sensor for implementing additional gain on the resultant voltage signal, and the same is finally converted to digital bits to obtain an output signal of with enhanced gain.