CMOS TDI Charge Transfer Structure for Low-Noise Image Summing

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Solution Overview

Problem

CMOS image sensors struggle to implement Time-Delay-Integration (TDI) due to their inability to perform charge transfer summing, which is necessary for low noise advantage, and require special fabrication processes and operating voltages outside normal circuit ranges.

Innovation Solution

A two-dimensional parallel charge transfer structure using CMOS image sensor pinned photodiodes connected by two-phase transfer gates with barriers and wells configured for unidirectional charge flow, along with microlenses and color filters to enhance optical collection and spectral performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If CCD image sensors are used to implement Time-Delay-Integration, then low noise advantage and charge transfer summing are achieved, but special fabrication process and operating voltages outside normal circuit range are required

Engineering Contradiction:

Improvelow noise advantageVSAvoidspecial fabrication process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the operating parameters by using standard CMOS voltages and fabrication processes instead of specialized CCD requirements. The transfer gates use conventional CMOS transistor structures with standard doping regions, allowing operation within normal circuit voltage ranges while maintaining TDI functionality.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent copies the essential TDI charge transfer functionality into standard CMOS architecture. By using pinned photodiodes with transfer gates that replicate the charge transfer mechanism of CCDs, the invention achieves TDI operation using conventional CMOS manufacturing processes and circuit designs.

Inventive Principle:

Principle #26Copying

2Reliability

If CCD image sensors are used to implement Time-Delay-Integration, then charge transfer summing is achieved, but integration with other circuitry to drive, process and read out the signal is difficult

Engineering Contradiction:

Improvecharge transfer summingVSAvoidintegration with other circuitry

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the TDI charge transfer function with standard CMOS imaging circuitry. The pinned photodiodes and transfer gates are integrated within the same CMOS substrate, allowing seamless integration with drive, process, and readout circuitry using conventional CMOS interconnects and fabrication steps.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent creates a universal structure where standard CMOS components (pinned photodiodes, transfer gates, interconnects) perform multiple functions. The same CMOS fabrication process and circuit elements used for standard imaging can be adapted for TDI operation, eliminating the need for specialized separate circuitry.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If normal CMOS image sensors are used, then integration with other circuitry is easy, but charge transfer summing required for low noise advantage of TDI cannot be performed

Engineering Contradiction:

Improveintegration with other circuitryVSAvoidcharge transfer summing capability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent segments the pixel structure into distinct functional regions: pinned photodiode regions for charge generation, transfer gate regions for charge transfer, and readout circuitry. This segmentation allows standard CMOS integration while incorporating the specific charge transfer summing capability needed for TDI operation through dedicated transfer gate structures between pixel columns.

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

Enables loss-less and noise-free synchronization of image readout with moving objects, achieving high optical collection efficiency and integrating seamlessly with other circuitry.

Implementation Method 1

a two dimensional parallel charge transfer structure comprising at least one column of CMOS image sensor pinned photodiodes

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

disposed so as to direct photons between the transfer gates into the photodiodes

Methodology Applied

Scientific EffectOptical focusing: Lens

Data Source

PatentUS12046624B2Time delay integration structure for complementary metal-oxide semiconductor imaging sensor

Publication Date: 2024.07.23 FAIRCHILD IMAGING INC

AI summary

A system is provided for time delay integration in complementary metal oxide semiconductor imaging sensors, the system comprising: a two dimensional parallel charge transfer structure comprising at least one column of CMOS Image sensor pinned photodiodes; each the diode in the column being connected to the next the diode by a two phase transfer gate, each the transfer gate having a barrier and a well configured such that a flow of charge in the column is unidirectional.