Technology of CMOS Image Sensorhome.sogang.ac.kr/sites/aiprc/sub_05/Lists/b6/Attachments/23/07... · Digital Imaging Solutions for you !! 2 1. Market Information 2. Technology of

SiliconFile Technologies Inc.

Technology of CMOS Image Sensor

Digital Imaging Solutions for you !! 2

1. Market Information

2. Technology of CMOS Image Sensor

3. New Challenges to Face

Contents


Technology Requirements

Total Camera Chipset Solution

FAB Process Package

Color Filter /

Micro LensTest

High sensitivity

Low Dark level

Pixel (BSI)

0.13um /90nm CMOS Imager Process

with High Productivity for Huge Quantity

High QualityCMOS Image Sensor

Solid CFA/Microlens Process

(Primary/Complementary)

Image Sensor &

Logic Test Solution

Lens/Module

High Quality

ISP (EDoF, Scalado)

Qualified Partners ISP : Image Signal Processor

Low Noise

Low Power

Analog CircuitHigh Speed Interface

MIPI/SMIA (LVDS)


Pictures & Products


Top View of Image Sensor

Digital Block (ISP)

Pixel

Driver

CDS

Pixel array ADC, ASP

2

2

4

PLL


Block Diagram


What is CMOS Image Sensor ?

Unit Pixel Function

Photon to charge

conversion : Quantum

Efficiency(QE)

Photo diode Capacitor ADC

Charge Charge to voltage

conversion :

Conversion

Efficiency (uV/e)

Voltage Digital

Data

Output

Analog to

Digital

Conversion

Photon

Flux

Quantum Efficiency : e / ph = e / lux . m2 . sec

Conversion Efficiency : uV / e

Sensitivity : ( Q.E x C.E ) x photodiode area : uV / lux . sec

CMOS image sensor is an opto-electronic device which converts incident photon flux to digital

signal . Incident light goes through the several conversions in CMOS sensor, such as photon to

charge conversion(Quantum Efficiency : QE), charge to voltage conversion(Conversion

Efficiency : uV/e) followed by analog to digital conversion. And it finally results in electrical digital

signal .


Schematic of Unit Pixel

Bias

Output

Sx

Substrate

Rx

VDD

3Transitor + PD

Unit Pixel Unit Pixel

Bias

Output

Sx

Substrate

Tx

Rx

VDD

4Transitor + PD


Cross section of Pixel

Photodiode

Poly silicon

Metal 1

Metal 2

Color Filter

Micro Lens

Green

10

Block Diagram of SFT

Pixel Array

BGBG ….

GRGR….

.

.

.

CDS / Memory Buffer / Reset Clamp

Column Decoder

PLL /

Clock

Control

Block

Row

Decoder

Swap/Mux

Auto White

Balance

Control

G R/B

ADC ADC

Programmable

Gain Control

Black Level

Calibration

ADC Driver

Sensor Control and Digital Image Signal Processing Block

SiliconFile Technologies Inc. 11

Pixel Array

Reset

Transfer

Select

VDD

VDD

VDD

VDD

VDD

VDD

j–1 th column jth column j+1th column

i–1th row

ith row

i+1th row


Pixel Operation

Exposure time

Reset

Transfer

Selectx

Write

Reset

Write

Signal

①

②

③

④

Exposure time

①

②

③

④

HBLANK

Store image data to CDS circuit Read out image data from CDS circuit by column by column

One Line

① PD를 초기화 시킨다.

② PD에 노출을 시작한다.

③ 설정했던 노출 시간이 지나면, Reset data를 읽어 CDS에 저장한다.

④ 설정했던 노출 시간이 지나면, Signal data를 읽어 CDS에 저장한다.


Rolling Shutter

VSYNC

VSYNC

VSYNC

VSYNC

VSYNC

Integration

domain

Scan

domain

row_1

row_2

row_n

Frame ith

row_1

row_2

row_n

Frame i+1th

row_1

row_2

row_n

Frame i+2th

row_1

row_2

row_n

Frame ith

row_1

row_2

row_n

Frame i+1th

row_1

row_2

row_n

Frame i+2 th

Exposure time

Exposure time

Exposure time


CDS and ASP

Write signal

Write reset

Pixel bias

TxRx

VDD

VDD VDD

VDD

TxRx

SxSx

-

+

Read signal

Read reset

WBA

ADC AG

j th column select j -1 th column select

CDS

ISP(Digital)


Image Signal Processor Pipeline

RGB gain

VSYNC, HSYNC, D[7:0], PCLK, STROBE

10bit ADCAG gainC.I

D.P.CN.R

Lens Correction

HistogramScaling

Color Correction RGB2YUV

Gamma Correction

EdgeEnhancement

WindowingNoise

Reduction

BrightColor

Saturation

ImageScaling

Image EffectRangeControl

YUV2RGB Formatter

AWB AE AE, AF

AE, AWB, AF

BLCAuto

Flicker


Image Processing Flow

CMOS

Image

Sensor Chip

GretagMacBeth

Chart

DSC of Sony

Bayer Image

Color

Inter-

polation

Full image

interpolated

Our Present Work

Color

Correction


Market Requirement

2007 2008 2009 2010

3

5

8

10

0

Year

Pix

el n

um

ber

(M

ega)

Mobile phone

application

2

High Resolution

High Frame Rate

Natural Image

Low Power Consumption

* Small Pixel Size

* High Frame Rate Readout Circuit

* Enhanced ISP & Special Function

like JPEG/EDoF


Hot issue in Small Pixel Technology

1. Low Sensitivity

2. Low Charge Capacity

3. Color Cross Talk

4. Pixel Uniformity and Noise

1. Shared Pixel Structure

2. BSI (BackSide illumination)

3. Decrease Backend Height

4. Dual Microlens

5. Light-guide

Approach to solve the issue


Structure of Shared Pixel

Output

Sx

Rx

VDD

Tx2

Tx1

Output

Sx

Rx

VDD

Tx3

Tx1

Tx2

Tx0

1.75T pixel ( 7Tr/4pixel )2.5T pixel (5Tr/2pixel)

Process of BSI (BackSide illumination)

BSI

Flow FAB Process Wafer Bonding Thinning PAD & CFA

Handling Wafer

SiPD

Al

FD

PAD

T

S

V

Oxide

SiPD

Al

FD

PAD

T

S

V

Oxide

SiPD

Al

FD

PAD

T

S

VPAD

Oxide

SiPD

Al

FD

PAD

T

S

V

Oxide

~

3um


Hot issue in Analog Circuit

1. High Speed Readout Circuit for High Frame Rate

2. Low Power Consumption for reducing dark current

3. LVDS solution for EMI issue and High Speed I/O


High Frame Rate : Applications


High Frame Rate Readout Circuit

1. High Speed Analog to Digital Converter in CIS


High Frame Rate Readout Circuit

1. High Speed Analog to Digital Converter in CIS – Column Parallel ADC Arch.

• Single-Slope Integration

+ Good linearity

+ Simple circuits

- Slow if high resolution is required

• Successive Approximation

+ High speed

- Large circuit size if high resolution is required

• Cyclic

+ High speed

+ Suitable for high resolution

- Relatively power hungry due to amplifiers


High Speed Digital Interface (Parallel Bus)

Traditional Interface : Parallel I/O Bus

- Power consumption & noise ( affect EMI issue)

- Skew between clock and data lanes (burden to high speed)

- Required PCB space and routing challenges drives up cost


Benefits :

- High Speed (~ 1GHz/ch )

- Low Power Consumption

- Enhance EMI issue

- Cost Effective (Reduce # of pin)

- Standards interface in mobile devices

High Speed Digital Interface (LVDS)

LVDS : MIPI, SMIA ..


Hot issue in Digital Circuit

1. Enhanced Image Signal Processor

2. Special Function : EDoF / Scalado JPEG

28

Image quality Key factors on Image

1. Sharpness

It is arguably the most important single image quality factor:

It determines the amount of detail an image can convey

2. Noise

Noise is a random variation of image density, visible as grain in film

and pixel level variations in digital images.

It arises from the effects of basic physics ( the photon nature of light and the thermal energy of heat)

inside image sensors.

3. Color accuracy

Color accuracy is an important but ambiguous image quality factor.

Many viewers prefer enhanced color saturation; the most accurate color isn't necessarily the most pleasing.

Nevertheless it is important to measure a camera's color response:

its color shifts, saturation, and the effectiveness if its white balance algorithms.

4. Dynamic range and contrast (Exposure Accuracy)

Dynamic range (or exposure range) is the range of light levels a camera can capture.

High contrast (shown on the right) usually involves loss of dynamic range—

loss of detail, or clipping, in highlights or shadows— when the image is displayed.

Reference : www.imatest.com

29

Example) Sharpness Image


30

Example) Noise Image


31

Example) Color Accuracy


32

Example) Dynamic range (Contrast)


Documents

Technology of CMOS Image Sensorhome.sogang.ac.kr/sites/aiprc/sub_05/Lists/b6/Attachments/23/07... · Digital Imaging Solutions for you !! 2 1. Market Information 2. Technology of