Dual-Ported Photodiode Imaging Array Dynamic Range Extension

Solution Overview

Problem

Conventional imaging arrays face limitations in dynamic range, leading to loss of image detail when capturing high-contrast scenes, as they saturate at both low and high light levels, and increasing the dynamic range with logarithmic pixels increases costs and reduces camera sensitivity.

Innovation Solution

An imaging array with dual-ported photodiodes and a charge conversion circuit, where the controller varies the potential on the second gates during exposure to extend the dynamic range without saturating, allowing for linear signal representation across a wider range of light intensities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of information

If logarithmic photodiodes are used to extend dynamic range, then the dynamic range increases, but the fill factor decreases and cost increases

Engineering Contradiction:

Improvedynamic rangeVSAvoidfill factor

Core Design Contradiction:

Loss of informationVSArea of stationary object

Solution Approach 1:

The photodiode is divided into two separate ports: a first port for capturing low light levels and a second port for capturing high light levels. Each port has its own readout circuit, allowing the imaging array to capture a wider dynamic range without requiring logarithmic photodiodes, thus maintaining a high fill factor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a temporal dimension by sequentially activating different ports during the exposure period. The controller activates the first port initially to capture low light levels, then activates the second port to capture high light levels, effectively extending the dynamic range through time-based segmentation rather than spatial segmentation.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Loss of information

If logarithmic photodiodes are used to extend dynamic range, then the dynamic range increases, but the manufacturing cost increases

Engineering Contradiction:

Improvedynamic rangeVSAvoidmanufacturing cost

Core Design Contradiction:

Loss of informationVSEase of manufacture

Solution Approach 1:

The photodiode is divided into two separate ports: a first port for capturing low light levels and a second port for capturing high light levels. Each port has its own readout circuit, allowing the imaging array to capture a wider dynamic range without requiring logarithmic photodiodes, thus maintaining a high fill factor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a temporal dimension by sequentially activating different ports during the exposure period. The controller activates the first port initially to capture low light levels, then activates the second port to capture high light levels, effectively extending the dynamic range through time-based segmentation rather than spatial segmentation.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Area of stationary object

If conventional photodiodes are used, then the fill factor remains high, but the dynamic range is limited and saturation occurs

Engineering Contradiction:

Improvefill factorVSAvoiddynamic range

Core Design Contradiction:

Area of stationary objectVSLoss of information

Solution Approach 1:

The photodiode is divided into two separate ports: a first port for capturing low light levels and a second port for capturing high light levels. Each port has its own readout circuit, allowing the imaging array to capture a wider dynamic range without requiring logarithmic photodiodes, thus maintaining a high fill factor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically switches between different ports during the exposure period based on the light intensity. The controller monitors the charge accumulation and activates the second port when the first port approaches saturation, allowing the system to adapt to varying light conditions and extend the effective dynamic range.

Inventive Principle:

Principle #15Dynamics

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 extends the dynamic range of the imaging array, preventing saturation and maintaining image detail across a broader light intensity range without increasing costs or reducing camera sensitivity, while allowing for accurate image representation.

Implementation Method 1

each pixel includes a photodetector that measures the amount of light that falls on some portion of the pixel area

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

the controller varies the potential on the second gates such that charge flows through the second gates of pixel sensors that are exposed to light intensities greater than a first threshold intensity

Methodology Applied

Scientific EffectElectric field control: Electric Field

Data Source

PatentUS8130294B2Imaging array with non-linear light response

Publication Date: 2012.03.06 FAIRCHILD IMAGING INC

AI summary

An imaging array and method for capturing an image utilizing the same are disclosed. The imaging array includes an array of pixel sensors in which each pixel includes a dual-ported photodiode or photogate and a charge conversion circuit. The charge conversion circuit generates a voltage signal that is a function of a charge on the dual-ported photodiode. The controller applies a potential that varies over the exposure to the second gates in the dual-ported photodiodes, each second port passing charge stored in the photodiode connected to the second port when a potential in the photodiode exceeds the applied potential. The potential is chosen such that charge flows through the second gates of pixel sensors that are exposed to light intensities greater than a first threshold intensity during the exposure.