Imaging Pixels With Non-Destructive Readout Floating Gate
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Solution Overview
Problem
Conventional image sensors are limited by destructive readout of charge from the floating diffusion region, which restricts the functionality of imaging pixels and prevents multiple non-destructive sampling of light intensity.
Innovation Solution
The implementation of imaging pixels with a floating gate that allows non-destructive readout capabilities, enabling repeated sampling of charge accumulation without altering the substrate voltage, thereby enabling multiple measurements of light intensity over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If charge is read out destructively from the floating diffusion region, then the readout process is simple and fast, but the functionality of the imaging pixel is limited and only one readout is possible
Solution Approach 1:
The pixel structure is segmented into distinct functional regions: a photodiode for charge generation, a floating diffusion region for charge accumulation, and a floating gate for non-destructive readout. This segmentation allows the charge to be read out multiple times without being consumed, enhancing pixel functionality while maintaining manageable structural complexity through modular design
Solution Approach 2:
A floating gate is introduced as an intermediary element between the photodiode and the readout circuitry. This floating gate acts as a mediator that can store and transfer charge information multiple times without destroying the original charge signal, enabling repeated non-destructive readouts and significantly improving pixel adaptability
2Measurement precision
If charge is read out destructively, then the readout process is straightforward, but multiple sampling of light intensity cannot be performed
Solution Approach 1:
The floating gate enables the system to discard the readout process temporarily while preserving the charge information. The charge can be read out, then recovered and stored in the floating gate for subsequent readouts, allowing multiple sampling operations without permanent loss of the original charge information
Solution Approach 2:
The floating gate creates a copy of the charge information that can be read out multiple times. Instead of reading the original charge directly (which would destroy it), the system creates a replicable copy in the floating gate, enabling repeated measurements of light intensity without depleting the source charge
3Productivity
If non-destructive readout with floating gate is implemented, then multiple sampling and dynamic range enhancement are enabled, but the pixel structure becomes more complex
Solution Approach 1:
The floating gate structure serves multiple functions simultaneously: it acts as a charge storage element, a transfer gate, and a readout interface. This multi-functionality enables the pixel to perform multiple sampling operations, dynamic range enhancement, and various imaging modes without requiring proportionally more complex circuitry, thereby improving productivity while controlling complexity
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 enhances the dynamic range of image sensors by allowing repeated sampling of light intensity, distinguishing between pixels that saturate at different times and reducing noise in low-light images, thereby improving image quality and functionality.
Implementation Method 1
Each image pixel in the array includes a photodiode that is coupled to a floating diffusion region via a transfer gate. Each pixel receives incident photons (light) and converts the photons into electrical signals.
Data Source
AI summary
An image sensor may include imaging pixels with non-destructive readout capabilities. Each imaging pixel may include a substrate having a photosensitive area that generates charge in response to incident light. The charge may accumulate at a front side of the substrate adjacent to a floating gate. The voltage of the floating gate may depend on how much charge is accumulated. The voltage of the floating gate may be repeatedly sampled to monitor the amount of incident light received over time. A first reset transistor may clear the substrate of accumulated charge. A second reset transistor may reset the voltage of the floating gate. The imaging pixel may be split between multiple wafers if desired and may include nMOS and pMOS transistors.