CMOS Image Sensor Pixel Circuit with Dynamic Conversion Gain Adjustment
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Solution Overview
Problem
Conventional CMOS image sensors face challenges in achieving a balance between high sensitivity and large dynamic range, often resulting in image lag or reduced signal-to-noise ratio due to limitations in conversion gain and full well capacity.
Innovation Solution
A photo-sensing pixel circuit with a conversion gain adjustment unit that operates in multiple modes, adjusting the number of transistors to optimize conversion gain based on light source brightness, allowing for both high sensitivity and large dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the photo-sensing part has a high full well capacity (FWC) and the CMOS image sensor has a large conversion gain, then the signal sensitivity is improved, but the voltage output to the backend circuit becomes too low causing image lag
Solution Approach 1:
The patent implements a dual-gain signal conversion circuit that can dynamically switch between high conversion gain and low conversion gain modes. The circuit includes a first signal conversion circuit with high conversion gain and a second signal conversion circuit with low conversion gain, allowing the system to adaptively select the appropriate gain level based on input signal conditions, thereby resolving the contradiction between signal sensitivity and backend circuit compatibility
Solution Approach 2:
The patent changes the conversion gain parameter by providing multiple signal conversion circuits with different gain characteristics. The system can switch between these circuits to alter the conversion gain parameter, enabling high sensitivity when needed while preventing image lag by using appropriate gain levels for different signal conditions
2Measurement precision
If the FWC of the photo-sensing part is reduced to maintain high conversion gain, then signal sensitivity is improved, but the dynamic range is sacrificed
Solution Approach 1:
The patent implements a dual-gain signal conversion circuit that can dynamically switch between high conversion gain and low conversion gain modes. The circuit includes a first signal conversion circuit with high conversion gain and a second signal conversion circuit with low conversion gain, allowing the system to adaptively select the appropriate gain level based on input signal conditions, thereby resolving the contradiction between signal sensitivity and backend circuit compatibility
Solution Approach 2:
The patent changes the conversion gain parameter by providing multiple signal conversion circuits with different gain characteristics. The system can switch between these circuits to alter the conversion gain parameter, enabling high sensitivity when needed while preventing image lag by using appropriate gain levels for different signal conditions
3Adaptability or versatility
If a CMOS image sensor with smaller conversion gain is designed, then the photo-sensing part can have high FWC and large dynamic range, but signal sensitivity inside the signal conversion circuit is reduced
Solution Approach 1:
The patent implements a dual-gain signal conversion circuit that can dynamically switch between high conversion gain and low conversion gain modes. The circuit includes a first signal conversion circuit with high conversion gain and a second signal conversion circuit with low conversion gain, allowing the system to adaptively select the appropriate gain level based on input signal conditions, thereby resolving the contradiction between signal sensitivity and backend circuit compatibility
Solution Approach 2:
The patent changes the conversion gain parameter by providing multiple signal conversion circuits with different gain characteristics. The system can switch between these circuits to alter the conversion gain parameter, enabling high sensitivity when needed while preventing image lag by using appropriate gain levels for different signal conditions
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
Enables the image sensor to maintain high sensitivity and signal-to-noise ratio across varying illumination conditions by dynamically adjusting conversion gain, thereby overcoming the limitations of conventional CMOS image sensors.
Implementation Method 1
The photo-sensing part senses a light source and generates a corresponding number of electrons
Data Source
AI summary
A photo-sensing pixel circuit including a photo-sensing part, a transfer transistor, a plurality of adjustment transistors, and an output circuit is provided. The photo-sensing part senses a light source and generates a corresponding number of electrons. The transfer transistor coupled to the photo-sensing part has a floating node and converts the electrons generated by the photo-sensing part into a voltage signal. The adjustment transistors have a first end and a second end, wherein the first end is coupled to a power supply, and the second end is coupled to the transfer transistor via the floating node. The output circuit coupled to the transfer transistor outputs a sensing signal according to the voltage signal, wherein the sensing signal is corresponding to the brightness of the light source. The adjustment transistors operate in at least two operation modes. Different numbers of the adjustment transistors are turned on in different operation modes.