Reference Pixel Sensor Cell for Leakage Cancellation

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Solution Overview

Problem

Global shutter image capture methods suffer from inefficiencies due to varying hold times on the floating diffusion node, leading to signal leakage and degradation, especially in high-speed image capture scenarios, where photon-generated carriers and leakage through the reset gate to Vdd node impact the signal readout.

Innovation Solution

Incorporating a reference pixel sensor cell connected to Vdd or a reference voltage, which remains in a reset mode and is not influenced by photons, allowing it to provide a reference signal to correct for leakage variations across the active light sensing regions, thereby compensating for signal losses in active pixel sensor cells.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If global shutter method is used to capture high speed objects, then image artifact issue is solved, but signal leakage and degradation occur due to varying hold times on floating diffusion node

Engineering Contradiction:

Improveimage capture accuracy for high speed objectsVSAvoidsignal leakage on floating diffusion node

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

A reference pixel sensor cell is introduced as an intermediary element that does not capture image signals but instead measures the leakage current on the floating diffusion node. This reference cell acts as a mediator between the varying hold times and the actual image signals, allowing the system to quantify and compensate for signal degradation without compromising the primary imaging function.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system implements a feedback mechanism where the reference pixel continuously measures leakage current during the hold period, and this measurement is used to adjust and compensate for signal degradation in the active pixels. The leakage measurement from the reference cell feeds back into the signal processing pipeline, enabling real-time correction of global shutter artifacts.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If reference pixel sensor cell is added to correct for leakage, then global shutter efficiency is improved, but device complexity increases

Engineering Contradiction:

Improveleakage signal measurement accuracyVSAvoidpixel array structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The pixel array is segmented into two functional types: active pixels for image capture and reference pixels for leakage measurement. This segmentation allows the system to separate the imaging function from the measurement function, enabling precise leakage characterization without interfering with the primary imaging task. The reference pixels are strategically distributed throughout the array to provide localized leakage measurements.

Inventive Principle:

Principle #1Segmentation

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 enables improved global shutter efficiency by accurately calculating and compensating for leakage, reducing image degradation and artifacts caused by varying hold times and photon-generated carriers, ensuring more accurate image capture.

Implementation Method 1

photon generated leakage signals which vary by locality within the active light sensing regions

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS8836835B2Pixel sensor cell with hold node for leakage cancellation and methods of manufacture and design structure

Publication Date: 2014.09.16 GLOBALFOUNDRIES US INC

AI summary

A reference pixel sensor cell (e.g., global shutter) with hold node for leakage cancellation, methods of manufacture and design structure is provided. A pixel array includes one or more reference pixel sensor cells dispersed locally throughout active light sensing regions. The one or more reference pixel sensor cells provides a reference signal used to correct for photon generated leakage signals which vary by locality within the active light sensing regions.