CCD versus CMOS - Optical Sciences

Report
Cameras for scientific experiments
A brave attempt to give an overview of the different types and their pros & cons
Grouptalk Optical Sciences, may 8 2012
Jeroen Korterik
Introduction
Lots of different types of cameras
Each working principle has it's own strong and weak points
Which type to use?
How to use it for optimal results?

Introduction: terminology
Analog film
Analog, electronic (CCD/CMOS, PAL/NTSC)
Digital (CCD/CMOS)
Color vs
monochrome
CCD versus CMOS
CCD: charge coupled device
Electrons from photodetector (diode)
charge a capacitor
Charges are shifted out towards the
output amplifier row by row, pixel by pixel
Advantage:
low noise
Backdraws:
Expensive: not CMOS compatible
High powerconsumption
Shift register
Output
amplifier
CCD versus CMOS
CMOS: Complementary Metal Oxide Semiconductor
1) Electrons from photodetector (diode)
charge a capacitor
2) rows of charges are selected by switching
on/off CMOS transistors
•Parallel processing: fast readout
•Cheap; standard CMOS technology
•Low power
•Traditionally noisier than CCD but CMOS
is catching up
Performance factors (part1)
Quantum efficiency (QE)
•Wiring and circuitry around/above every
pixel's photodiode decreases fill factor
and therefore the QE as well
•Workaround: etch the backside of the
sensor and illuminate from the back
('back illuminated CCD/ CMOS')
→already seen in 200€ photocameras!
Dark counts
•Spontaneous emission of electrons
from photodiode
•Constant offset in signal due to dark
counts can be corrected but
sqrt(dark counts) = shot noise!
•Strong dependance on temperature
•Liquid nitrogen models (LN): down to
-120 degC
•Peltier cooled models (TE): down to
-70 degC
•Backdraw: cooling might also reduce
the QE
Performance factors (part2)
Readout noise
•After illumination, charges are read out (charge transport, amplifier, ADC)
•This adds noise to the signal
•Solution1: longer illumination times
•Solution2: slow readout (slow ADC) → some camera's have selectable ADC speed
•Solution3: ICCD, EMCCD, sCMOS
Andor Ikon-L 936 TE cooled CCD
ADC speed [Mhz] Readout noise [e-/pix]
0.05
1
3
5
2.9
7.0
11.7
31.5
Advanced techniques for high speed & low light levels: ICCD, EMCCD, sCMOS
Intensified CCD (ICCD)
Intensifier in front of CCD amplifies optical signal
* low QE (up to 40% for gen4 intensifier)
* ns gating possible
* intensifier increases shotnoise by a factor sqrt(2)
Electron multiplier CCD (EMCCD)
Electrons out of CCD get multiplied before ADC
* high QE (up to 90% for back illuminated CCD)
* EM increases shotnoise by a factor sqrt(2)
Scientific CMOS (sCMOS)
improved CMOS sensor
* high QE ~70%
* very high speed ~500Mpix/s
* low readout noise 1.2 e-/pix
* low dark current 0.2 e-/pix/s
1D cameras
Linescan CCD
* High frame (line) rates : tens of kHz
* low noise
NMOS Linear Image Sensor
* rectangular pixels: 25um wide, 2.5mm high
→ non critical alignment, catch all the light
* high dynamic range due to large quantum well
→ measure small fluctuation on large background
Homebuilt NMOS LIS cameras:
→ with spectrograph: full spectrum per lasershot
1) Push setup 1 kHz
2) Shove setup 5 kHz
TOF camera
LED 20 MHz
Time of flight camera (TOF)
* measures intensity and time delay of reflections
* modulated light source LED @ 20 MHz
* CMOS sensor
* 'dual phase lockin amplifier' per pixel
Grayscale intensity
Colorscale TOF
Streak Camera
Horizontal direction: intensity vs position (spectrum)
Vertical direction: arrival time with resolution down to 100fs

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