Image Sensor Reset Compensation Block for Darkening Effect
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Solution Overview
Problem
Conventional CMOS image sensors experience a darkening effect when capturing bright objects, such as light sources, due to the reset voltage signal deviating from a preferable range, leading to image distortion and reduced quality.
Innovation Solution
Incorporating a reset voltage check block and compensation block to maintain a minimum voltage level for the reset signal, using a correlated double sampling method to compare and adjust the reset signal levels, ensuring the reset signal remains within a preferable range and compensating for deviations to prevent image distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the reset signal is generated without voltage level control, then the device complexity is reduced, but the image quality deteriorates due to darkening of bright objects
Solution Approach 1:
The patent applies parameter changes by monitoring the reset signal voltage level and dynamically adjusting the reset operation based on the detected voltage threshold. When the reset signal voltage falls below a predetermined threshold, the system modifies the reset behavior to compensate for the voltage deviation, thereby maintaining image quality without significantly increasing device complexity.
Solution Approach 2:
The patent implements feedback by introducing a voltage detection mechanism that monitors the reset signal level and uses this information to control the reset transistor operation. The feedback loop ensures that when voltage deviation is detected, the system automatically adjusts the reset process to prevent darkening of bright objects in the captured image.
2Ease of operation
If the reset signal voltage is not maintained within a preferable range, then the ease of operation is improved, but the measurement precision deteriorates due to voltage deviation
Solution Approach 1:
The patent applies self-service by enabling the system to automatically detect and correct reset signal voltage deviations without external intervention. The voltage detection circuit continuously monitors the reset signal and self-adjusts the reset operation based on the detected voltage level, maintaining precise voltage control while keeping the operation simple for the user.
3Illumination intensity
If strong light is inputted from the object, then the illumination intensity is improved, but the image quality deteriorates due to darkening effect
Solution Approach 1:
The patent applies preliminary anti-action by detecting voltage deviations caused by strong light input before they can cause significant image distortion. The voltage detection circuit monitors the reset signal in advance and preemptively adjusts the reset operation to counteract the darkening effect that would otherwise occur when strong light illuminates the photodiode during the reset phase.
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 reduces the darkening phenomenon in bright objects, enhancing image sensor quality by maintaining accurate voltage levels and improving image reproduction.
Implementation Method 1
the photodiode (PD) 201 generates the photo-electrons in response to the inputted light
Implementation Method 2
A reset transistor (Rx) 204 coupled to a supply voltage Vdd resets the floating node FN to a predetermined level by eliminating the photo-electrons charged in a capacitor 203 of the floating node FN
Implementation Method 3
A driving transistor (Dx) 205 served as a source follower buffer amplifier has a gate coupled to the floating node FN
Data Source
AI summary
An image sensor for obtaining a digital image data by using a correlated double sampling method unrelated to an intensity of inputted light includes a pixel array including N×M unit pixels; a reset voltage check block for receiving each reset signal outputted from each unit pixel and comparing a level of each reset signal with a minimum level of a preferable reset signal to thereby generate a reset compensation control signal; a reset voltage compensation block for compensating the reset signal outputted from each unit pixel in response to the reset compensation control signal to generate a compensated reset signal; and an analog to digital converter for deriving an analog image data by using a data signal outputted from the pixel array and the compensated reset signal to convert the analog image data into the digital image data.