Integration Capacitor Phase Switching for Full Well Capacity Extension

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Solution Overview

Problem

Conventional photo detection systems face limitations in full well capacity, leading to signal saturation and reduced dynamic range, especially in high background and high signal level applications, which restricts image resolution and increases noise equivalent delta temperature (NEDT).

Innovation Solution

A detector circuit with an integration capacitor that operates in multiple phases, using switch matrices to rotate the capacitor and perform charge subtraction, allowing for increased full well capacity without sacrificing unit cell size or sensitivity, through a method involving four-phase charge subtraction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the integration capacitor size is increased to extend full well capacity, then the dynamic range towards high intensities is improved, but the sensitivity towards low intensities deteriorates due to lower output voltage swing per photo generated charge carrier

Engineering Contradiction:

Improvefull well capacityVSAvoidsensitivity

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The integration process is divided into multiple frames, where each frame integrates a portion of the total signal charge. The integration capacitor processes charge in segments across successive frames rather than attempting to integrate all charge in a single frame, thereby maintaining both high full well capacity and high sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system uses periodic frame-based integration cycles, where the integration capacitor is repeatedly charged and discharged across multiple frames. This periodic operation allows the same capacitor to accumulate equivalent capacity proportional to the number of frames, achieving extended full well capacity without increasing capacitor size.

Inventive Principle:

Principle #19Periodic action

2Quantity of substance

If the integration time is reduced to avoid saturation in high signal level applications, then the full well capacity limitation is circumvented, but the integration time becomes insufficient to capture all generated charge carriers

Engineering Contradiction:

Improvecharge carrier captureVSAvoidintegration time

Core Design Contradiction:

Quantity of substanceVSDuration of action of moving object

Solution Approach 1:

The system performs preliminary integration in each frame for a duration optimized for sensitivity, then resets and continues integration in subsequent frames. This preliminary action in each frame allows charge carriers to be systematically captured across multiple time intervals, achieving total integration time exceeding the frame period without requiring each individual frame to integrate all charge.

Inventive Principle:

Principle #10Preliminary action

3Quantity of substance

If a larger integration capacitor is used to increase full well capacity, then the achievable image resolution deteriorates due to increased minimum spacing between detector sites

Engineering Contradiction:

Improvefull well capacityVSAvoidunit cell size

Core Design Contradiction:

Quantity of substanceVSArea of stationary object

Solution Approach 1:

The system dynamically extends the effective integration capacity by utilizing time (multiple frames) rather than statically increasing capacitor size. This dynamic approach allows full well capacity to scale with the number of frames while maintaining a compact capacitor size, thereby preserving small unit cell area and enabling high image resolution.

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

This approach enhances full well capacity, reduces noise, and maintains sensitivity, enabling wider dynamic range and improved image resolution, particularly in shot noise-dominated applications and high background conditions.

Implementation Method 1

an integration capacitor operable in two or more phases... The first plate of the integration capacitor is coupled to a first and a second switch, the first and second switches being configured to phase switch the integration capacitor

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

The CTIA integrates the current generated from a detector over a period of time to provide a measurable output voltage signal

Methodology Applied

Scientific EffectIntegration:

Data Source

PatentUS7436342B2Numerical full well capacity extension for photo sensors with an integration capacitor in the readout circuit using two and four phase charge subtraction

Publication Date: 2008.10.14 TELEDYNE SCIENTIFIC & IMAGING LLC

AI summary

A detector circuit having an integration capacitor coupled to an amplifier via a switch matrix and a comparator coupled to the amplifier, the integration capacitor operable in two or more phases, the switch matrix is configured to phase switch the integration capacitor, the comparator triggers the phase switch when the output voltage of the amplifier passes the threshold voltage of the comparator.