Buried-Gated Photodiode Floating Diffusion Control
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Solution Overview
Problem
3-transistor buried-gated photodiode devices are unsuitable for windowed arrays due to the floating diffusion node, which can inadvertently drive the pixel output line, causing corruption of sampled values when not addressed.
Innovation Solution
A 3-T pinned photodiode device configuration that includes a source follower transistor, a reset transistor, and a transfer transistor, with the floating diffusion node held low using a select timing signal, ensuring the device only drives the pixel output line when specifically addressed, allowing shared transistors and photodiodes across multiple pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 3-T pinned photodiode device is used, then the device structure is simple, but the floating diffusion node can inadvertently drive the pixel output line causing corruption
Solution Approach 1:
A select transistor is introduced as an intermediary component between the floating diffusion node and the pixel output line. This transistor acts as a controlled gate that prevents unauthorized signal transmission while allowing legitimate readout when selected, thus maintaining signal integrity without requiring complex device structures
Solution Approach 2:
The pixel array is divided into multiple segments or groups, each with its own select line and control mechanism. This segmentation allows independent control of different pixel groups, enabling the floating diffusion node to be properly managed in windowed array configurations while maintaining simple 3-T device structures
2Reliability
If the floating diffusion node is held low to prevent inadvertent driving, then signal integrity is improved, but additional control circuitry is required
Solution Approach 1:
The select transistor serves multiple functions: it acts as a switch to control pixel selection, a gate to prevent inadvertent output line driving, and part of the readout circuitry. This multi-functionality achieves signal integrity improvement without proportionally increasing control circuitry complexity
Solution Approach 2:
The control functions are merged into the existing pixel structure by integrating the select transistor with the floating diffusion node and output line infrastructure. This combining approach achieves the needed control functionality while minimizing additional circuitry by reusing existing structural elements
3Area of stationary object
If 3-T pinned photodiode devices are used in windowed arrays, then area is reduced, but the floating nature of the FD node causes corruption of sampled values
Solution Approach 1:
The select transistor acts as a mediator that enables safe area-efficient deployment of 3-T pinned photodiode devices in windowed arrays by controlling when the floating diffusion node can drive the output line, thus preventing sampling corruption while maintaining compact pixel area
Solution Approach 2:
The select transistor is configured to hold the floating diffusion node in a controlled state before readout operations begin. This preliminary control action prevents potential sampling corruption in advance, enabling reliable use of area-efficient 3-T devices in windowed array configurations
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 use of 3-T buried-gated photodiode devices in windowed arrays without inadvertently driving the pixel output line, reducing transistor and control line area requirements while maintaining accurate sampling.
Implementation Method 1
photons strike the photodiode 3 causing electrical charge to accumulate on the photodiode 3
Data Source
AI summary
A 3-T buried-gated photodiode device that is suitable for use in a windowed array. The 3-T buried-gated photodiode device is configured such that the floating diffusion (FD) node of the device is held low when the device is not being specifically addressed, which ensures that the device cannot drive the corresponding pixel output line unless it is specifically addressed.