September 03. 18. Cell Phone Cameras Are Small ... Mobile Phones. Digital Still Cameras. CMOS Image Sensor Market Growth
Visible Light CMOS Image Sensors
Dr. Eric R. Fossum Senior Fellow, Micron Imaging Micron Technology, Inc.
1
Outline 4 Introduction to CMOS image sensor pixels 4 Examples of sensors 4 Customer trends 4 CMOS image sensor technology trend 4 Thoughts on next 5 years
September 03
2
3Transistor (3T) CMOS APS
4 Use source-follower
M1 RST
“amplifier” to drive column bus Ipd
Vpix M2 SF Vpd Cpd
Col Bus
M3 RS
Vss Vout IL
September 03
3
Voltage on 3T Pixel vs. Time Photodiode Voltage integration starts
pixel reset level sampled
3V Net
2V
signal 1V
signal sampled
0V 33 ms
66 ms
Pixel sampled twice to remove variations in threshold voltage of pixel source-follower and reset level September 03
4
Simplified Signal Chain Photodiode Voltage integration starts
PIXEL
VDD
pixel reset level sampled
3V Net
2V
signal
RST
1V
signal sampled
0V 33 ms
RS COL BUS SHS
66 ms
GLOBAL
CS SIG
VLP HOR BUS
SHR
RST
VLN
PER COLUMN September 03
5
VLP
Imaging System on a Chip Digital Logic for • User Interface • Sensor Setup • Timing Generator • Digital Signal Processing –Color Processing –White Balance –Image Enhancement • Data Output Formatting
CMOS Active Pixel Color Imaging Array
Analog Signal Processing • Data Sampling • Noise Reduction • Gain September 03
Analog-To-Digital Conversion
6
Relative response
Spectral Response of Eye and Silicon 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 400
Human Eye
Silicon
500
600
700
800
900
Wavelength (nm) UV
September 03
NIR
7
1000
1100
Fill Factor 4 A pixel is divided into a sensing portion and a readout
portion 4 Fill factor is the ratio of sensing area to total area and
is typically about 20-30% Total pixel area Sensitive area
September 03
8
Color Filter Arrays and Microlenses
Microlens layer Color filter layer Metal opaque layer Photodiode Silicon substrate September 03
9
Resolution and Sensitivity 4 More pixels = high resolution 4 Smaller pixels = less sensitivity Scene
Image
Photons /pixel
Pixel pitch September 03
10
Optical Formats 7.8 mm
10
5.6 mm 3.6 mm Pixel Size (um)
CIF VGA 1.3M 2.1M
“1/4 in”
3.3M 4.1M
2.8 mm 1 1/7
1/6
1/5
1/4
1/3
Lens Format
September 03
11
1/2
2/3
Pictures from PC Camera Sensors
September 03
CIF Resolution
VGA Resolution
(352 x 288)
(640 x 480)
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1.3Mpixel High Speed Sensor 41280 ADCs per chip 45T pixel 4500 pictures per
second at full resolution 4Shutter from 1/30th sec
to 1/100,000th sec 4Shutter efficiency >
99.99% 4Rotating fan image ‡
1/33,000 sec = 30 usec Freeze frame shutter September 03
13
Pill Camera
Sensor and US$0.10
Pill Camera and US$0.25
4 Pixel Format: 256 X 256 4 Pixel Size: 10 µm X 10 µm 4 Frame Rate: 2 fps 4 ADC: On-Chip, 8 bits 4 Power Supply: 2.8 V Krymski 1998 September 03
4 Power: 3 mW 14
View inside small intestine
4 Mpixel sensor 240fps ERS
4 4 4 4 4 4 4
2352 x 1728 7 mm x 7 mm pixel pitch 16x10b digital output 240 fps ERS 960 Mbytes/sec at 66 MHz 4000 bits/lx-sec 3.3 volt operation
Krymski 2001 September 03
15
Customer Drivers 4 Incredibly fast price point erosion (2Mpixel CCD
now sells for $8 in Japan) 4 Voltage scaling required to be compatible with
companion chips (3.3V -> 2.8V ->…1.8V) 4 Power dissipation
