Photosensor Arrangement Using Back-Side Illumination and CDS
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Solution Overview
Problem
Photosensor arrangements face challenges in achieving high dynamic range due to noise sources such as photon shot noise, dark noise, and read noise, which degrade image quality and limit the maximum detectable signal strength.
Innovation Solution
A photosensor arrangement is designed with an amplifier, comparator, and capacitor configuration that includes reset circuitry and a feedback path, utilizing correlated double sampling (CDS) to remove reset noise and input offsets, and employing back-side illumination to place the capacitor over the photodiode, allowing for improved noise reduction and dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the photosensor area is increased to improve full well capacity and dynamic range, then the maximum detectable signal strength increases, but the device complexity and manufacturing difficulty increase due to the need for precise capacitor placement and back-side illumination structures
Solution Approach 1:
The patent implements back-side illumination architecture where the capacitor is positioned on the opposite side of the photodiode from the light source. This spatial reconfiguration allows the capacitor to overlie the photodiode in a different dimension, reducing interference with the optical path while maintaining electrical coupling, thereby enabling higher dynamic range without proportionally increasing device complexity
Solution Approach 2:
The patent changes the physical and electrical parameters of the photosensor arrangement by introducing a specifically sized capacitor (with area between 0.1 to 10 times the photodiode area) and configuring it with specific coupling characteristics. This parameter optimization allows the system to achieve high dynamic range (close to human eye's 150 dB) while controlling the full well capacity and noise characteristics without requiring excessive device complexity
2Object-affected harmful factors
If the capacitor area is increased to reduce photon shot noise and improve dynamic range, then the noise reduction effectiveness increases, but the full well capacity may be limited by the pixel area constraint
Solution Approach 1:
The patent optimizes the capacitor area parameter within a specific range (0.1 to 10 times the photodiode area) to achieve the right balance between noise reduction and full well capacity. By carefully selecting the capacitor area within this range, the system can reduce photon shot noise effectively while maintaining sufficient pixel area for adequate full well capacity
Solution Approach 2:
By placing the capacitor on the back side of the photodiode (opposite to the light source), the patent utilizes the third dimension (depth/z-axis) to accommodate the capacitor without consuming additional lateral pixel area. This allows the capacitor area to be optimized for noise reduction without being constrained by the two-dimensional pixel footprint
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 achieves a high dynamic range close to that of the human eye (150 dB) by reducing noise, particularly at low light levels, and enables accurate measurement of photo-generated charge with reduced photon shot and read noise, enhancing image quality.
Implementation Method 1
a photodiode 212 coupled to an input of a charge integrator circuit 214
Implementation Method 2
The photosensor arrangement may be configured in use to have back side illumination and the capacitor may be configured to overlie, at least partially, a photodiode of the photosensor arrangement
Data Source
AI summary
A photosensor arrangement may include an amplifier configured to receive charge from a photosensor device at a first input, and a second input configured to receive a first reference voltage. The amplifier may provide an output voltage on an output. A comparator has a first input at the output voltage, a second input at the first reference voltage and is configured to provide a compare output. A capacitor is configured to have a first plate coupled to the output of the amplifier and a second plate coupled to the first input of the comparator.