Image Sensor Polarizer Noise Cancellation
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Solution Overview
Problem
CMOS image sensors face challenges in reducing component volume, leading to decreased fill factor and full well capacity, and struggle with background noise in optical fingerprint recognition, affecting signal-to-noise ratio and accuracy.
Innovation Solution
An image sensor design that uses polarizers to separate incident light into polarized signals, with a readout circuit performing subtraction and integration operations to eliminate background noise, thereby increasing full well capacity and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the component volume of CMOS image sensor is reduced, then the sensor size is decreased, but the fill factor and full well capacity decrease
Solution Approach 1:
The sensor array is divided into multiple blocks, with each block containing unit pixels of the same polarity. Adjacent blocks have opposite polarities (first polarity and second polarity). This segmentation allows the sensor to maintain smaller component volume while preserving adequate full well capacity through differential processing of the segmented blocks.
Solution Approach 2:
The invention changes the polarity parameter of adjacent pixel blocks to be opposite (first polarity vs. second polarity). By alternating the polarity of adjacent blocks, the sensor achieves better signal-to-noise ratio and maintains effective full well capacity despite reduced component volume, as the differential readout cancels out common-mode noise and background light.
2Object-affected harmful factors
If background light occupies excessive percentage of full well capacity, then the signal-to-noise ratio decreases, but the fingerprint recognition accuracy is affected
Solution Approach 1:
The invention extracts and separates the background light signal from the fingerprint signal using polarizers. By placing polarizers at different orientations over adjacent pixel blocks, the background light (which is largely unpolarized or has random polarization) is differentially captured, allowing it to be subtracted out during image processing, thereby removing the harmful background noise while preserving the fingerprint pattern.
Solution Approach 2:
The invention converts the harmful background light into a useful signal by exploiting its polarization characteristics. The polarizers cause background light to be captured differently in adjacent blocks, transforming it from noise into a differential signal that can be subtracted during processing. This converts the harmful background illumination into a benefit for enhancing fingerprint contrast and recognition accuracy.
3Object-affected harmful factors
If polarizers are arranged on unit pixels, then the background noise is eliminated, but the device complexity increases
Solution Approach 1:
The polarizers in the invention serve multiple functions simultaneously: they act as optical filters to separate background light from fingerprint patterns, they create differential signals between adjacent blocks for noise cancellation, and they enable the sensor to operate effectively with reduced component volume. This multi-functionality justifies the added structural complexity by delivering multiple benefits from a single component addition.
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 effectively enhances the signal-to-noise ratio and accuracy of CMOS image sensors, particularly in optical fingerprint recognition, by eliminating background noise and increasing the capacity to accommodate more effective electrons without altering the sensor's size.
Implementation Method 1
the first polarizers being for changing the incident light into a first incident light having a first polarization direction, and the photoelectric conversion element receiving the first incident light and generating a plurality of first electrons; a plurality of second polarizers, arranged on another part of the unit pixels, and each of the second polarizers covering each unit pixel of the another part of the unit pixels, the second polarizers being for changing the incident light into a second incident light having a second polarization direction
Implementation Method 2
each of the unit pixels comprising a photoelectric conversion element, for generating electrons after receiving an incident light
Data Source
AI summary
The invention relates to an image sensor, including a substrate, a unit pixel, a first polarizer, a second polarizer, and readout circuit. First, incident light is emitted to the image sensor, and the first and second polarizers convert incident light into first and second incident lights respectively. Then, the photoelectric conversion element of the unit pixel covered by the first and second polarizers respectively generates first and second electrons after receiving the first and second incident lights respectively. Afterwards, the readout circuit performs subtraction and integral of the first electron and the second electron to generate a voltage signal corresponding to the number of electrons in the actual signal. Finally, repeat the above steps. Thereby, the image sensor of the invention effectively increases the full well capacity of the equivalent unit pixel, so as to improve the signal-to-noise ratio of the image sensor of the invention.