Image Sensor Dynamic Charge-Domain Sampling Fill Factor

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Solution Overview

Problem

Conventional CMOS image sensors with adjustable sensitivity face a trade-off between input-referred noise and dynamic range due to the need for extra hardware to adjust capacitance, which reduces the fill factor and increases manufacturing costs.

Innovation Solution

The image sensor employs dynamic charge-domain sampling with in-pixel amplification, using a charge-sampling pixel that converts the floating diffusion node voltage into a current with a variable time window and/or capacitance, allowing for programmable gain adjustment based on incident light levels without additional hardware, thereby enhancing detection sensitivity and reducing noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If extra hardware is added to adjust capacitance of the charge storage node, then adjustable sensitivity is achieved, but fill factor is reduced

Engineering Contradiction:

Improveadjustable sensitivityVSAvoidfill factor

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The patent merges the sensitivity adjustment function with the existing charge storage node by dynamically sharing it between signal level integration and reset level integration. This eliminates the need for separate adjustment hardware, maintaining high fill factor while achieving adjustable sensitivity through temporal multiplexing of the charge storage node.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces dynamic control of the charge storage node capacitance by selectively connecting it to different integration circuits (signal level or reset level) based on incident light intensity. This dynamic reconfiguration allows sensitivity adjustment without adding static hardware, resolving the fill factor contradiction.

Inventive Principle:

Principle #15Dynamics

2Adaptability or versatility

If extra hardware is added to adjust capacitance, then sensitivity adjustment is enabled, but device complexity increases

Engineering Contradiction:

Improvesensitivity adjustmentVSAvoidhardware complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The charge storage node is designed to serve multiple functions: it acts as both the signal level integration capacitor and the reset level integration capacitor depending on the operating mode. This multi-functionality eliminates the need for separate adjustment hardware, reducing device complexity while maintaining sensitivity adjustability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system uses its own charge storage node to perform sensitivity adjustment without requiring external adjustment components. The node dynamically serves itself by being reconfigured between different integration roles based on light intensity, eliminating dependency on extra adjustment hardware.

Inventive Principle:

Principle #25Self-service

3Device complexity

If fixed capacitance is used in S/H stage, then hardware is simplified, but adaptability to different light levels is reduced

Engineering Contradiction:

Improvehardware simplicityVSAvoidadaptability to light levels

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The effective capacitance of the charge storage node is changed by altering its connection state between signal level integration and reset level integration. This parameter change is achieved through control signals that switch the node's function, providing adaptability to different light levels without hardware modification.

Inventive Principle:

Principle #35Parameter changes

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 allows for improved signal-to-noise ratio and dynamic range without increasing hardware complexity, maintaining a high fill factor and reducing manufacturing costs by dynamically controlling the time window and capacitance according to light intensity.

Implementation Method 1

a pixel coupled to a floating diffusion region... a photodiode 102 and a transfer transistor 104

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

a first sample-and-hold capacitor coupled between a third supply voltage and a second supply voltage

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentEP3655992B1Image sensor with dynamic charge-domain sampling

Publication Date: 2021.08.18 SHENZHEN GOODIX TECH CO LTD

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AI summary

An image sensor(100) includes: a pixel(101) coupled to a floating diffusion region(FD); a reset select transistor(106) coupled between the floating diffusion region(FD) and a first supply voltage(VDD); an n-type source follower transistor(112) coupled between the first supply voltage(VDD) and a second supply voltage(GND), the n-type source follower(112) being operable to receive electrical signal from the floating diffusion region(FD); an n-type row select transistor(110) coupled between the first supply voltage(VDD) and the n-type source follower transistor(112); a first sample-and-hold capacitor(126) coupled between a third supply voltage(VRST) and the second supply voltage(GND); a first switch(118) coupled between the n-type row select transistor(110) and the first sample-and-hold capacitor(126); and a second switch(124) coupled between the third supply voltage(VRST) and the first sample-and-hold capacitor(126).