MOSCap Unit Cell for High Dynamic Range Image Sensors
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Solution Overview
Problem
Image capture devices are typically optimized for either bright or low ambient light scenes, leading to competing capacitance requirements that limit their dynamic range and pixel size, resulting in suboptimal performance in varying lighting conditions.
Innovation Solution
A high dynamic range unit cell with a Metal-Oxide-Semiconductor Capacitor (MOSCap) that functions as both a high-sensitivity anti-blooming gate and a low-sensitivity capacitor, allowing for reduced pixel size and improved well-capacity, enabling accurate light intensity signal generation in both low and high ambient light situations by controlling the threshold voltage and switch states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the image sensor uses components with low noise and low capacitance, then sensitivity in low ambient light scenes is improved, but the ability to store charge in bright ambient light scenes deteriorates
Solution Approach 1:
The patent implements dynamic switching between two operational modes using control circuitry that selects between a first capacitor (low capacitance) for low light conditions and a second capacitor (high capacitance) for bright light conditions. This dynamic reconfiguration allows the image sensor to adapt its charge storage capacity to match the ambient light conditions, resolving the contradiction between sensitivity and charge storage capacity.
Solution Approach 2:
The patent changes the capacitance parameter of the image sensor by providing at least two capacitors with different capacitance values and selectively connecting them to the photodiode based on ambient light conditions. This parameter change enables the sensor to optimize between low noise/low capacitance for sensitivity and high capacitance for charge storage, directly addressing the technical contradiction.
2Quantity of substance
If the image sensor is optimized for bright ambient light scenes with higher capacitance, then charge storage capacity is improved, but sensitivity in low ambient light scenes deteriorates
Solution Approach 1:
The patent implements dynamic switching between two operational modes using control circuitry that selects between a first capacitor (low capacitance) for low light conditions and a second capacitor (high capacitance) for bright light conditions. This dynamic reconfiguration allows the image sensor to adapt its charge storage capacity to match the ambient light conditions, resolving the contradiction between sensitivity and charge storage capacity.
Solution Approach 2:
The patent changes the capacitance parameter of the image sensor by providing at least two capacitors with different capacitance values and selectively connecting them to the photodiode based on ambient light conditions. This parameter change enables the sensor to optimize between low noise/low capacitance for sensitivity and high capacitance for charge storage, directly addressing the technical contradiction.
3Adaptability or versatility
If multiple anti-bloom switches are used to handle both low and high ambient light situations, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent makes the MOSCap serve multiple functions: it acts as an anti-blooming gate in low light conditions and as a storage capacitor in bright light conditions. This multi-functionality eliminates the need for separate anti-bloom switches for different lighting conditions, reducing device complexity while maintaining adaptability across ambient light conditions.
Solution Approach 2:
The patent changes the functional parameter of the MOSCap by selectively configuring it as either an anti-blooming gate or a storage capacitor based on ambient light conditions. This parameter change allows a single component to replace multiple specialized components, reducing the number of switches needed while maintaining versatility.
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
The solution enables image capture devices to operate effectively in a wide range of ambient light conditions with reduced pixel size, minimizing noise and parasitic capacitance, and accurately represent light intensity without the need for multiple anti-bloom switches, thus enhancing image quality.
Implementation Method 1
generate charge in proportion to light intensity received at the image sensor from a scene viewed by the image sensor
Implementation Method 2
charge generated by light incident on the photodiode accumulates on the MOSCap in response to the voltage at the input node being greater than the threshold voltage
Data Source
AI summary
According to one aspect, embodiments herein provide a unit cell comprising a photodiode, a MOSCap having an input node coupled to the photodiode, a reset switch selectively coupled between the MOSCap and a reset voltage, and a transistor coupled to the input node of the MOSCap, wherein, in a first mode of operation of the unit cell, the reset switch is configured in an open state and charge generated by light incident on the photodiode accumulates at the input node of the MOSCap in response to voltage at the input node being less than a threshold voltage, and wherein, in a second mode of operation of the unit cell, the reset switch is configured in the open state and the charge generated by the light incident on the photodiode accumulates on the MOSCap in response to the voltage at the input node being greater than the threshold voltage.