Electron Multiplying CCDs
An IntroductionSimon Tulloch
www.qucam.com
CCD60 128 x 128 CCD87/97 512x512 CCD201 1K x 1K
Image Area Store Area
Norm
al Seri
al re
gis
ter
Multiplication register
Multip
licatio
n re
giste
r
Multiplication register
Standard MOSFETamplifier
1e- in
1000e- signal out
Avalanche multiplication takesplace in Multiplication Register,using an HV clock (40-45Volts).
Commercially available :
Electron Multiplying CCDs
Flexible OperationE2V CCD201
3e noiseTo Observe:Absorption linesBright Emission LinesEmission lines superimposed on bright continuum
<<1e noiseTo Observe: Faint Emission Lines
clock left clock right
Conventional Amp.Electron Multiplying
Amplifier
Pot
enti
al E
nerg
yMultiplication Clocking 1
Gain electrode
In this diagram we see a small section of the gain register
Pot
enti
al E
nerg
yMultiplication Clocking 2
Pot
enti
al E
nerg
y
Gain electrode energised. Charge packets accelerated strongly into deep potential well.Energetic electrons loose energy through creation of more charge carriers (analogous tomultiplication effects in the dynodes of a photo-multiplier) .
Gain electrode
Pot
enti
al E
nerg
yMultiplication Clocking 3
Pot
enti
al E
nerg
y
Clocking continues but each time the charge packets pass through the gain electrode, furtheramplification is produced. Gain per stage is low, <1.015, however the number of stages is high so the total gain can easily exceed 10,000
Multiplication Noise
L3 CCD Noise Characteristics
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Mean of Signal
Var
ianc
e of
Sig
nal
Normal CCD
L3 Gain=12
L3 Gain=39
L3 Gain=283
2Effect is to increase the photon noise by a a factor of
Flat fields taken with an EMCCD show unusual statistics. The variancein the flat fields is no longer equal to the mean signal as is expectedwith photon statistics.
EMCCD becomes competitiveat lower exposure levels
With EM Gain: At low illumination, photons are resolved. Without EM Gain: object only just visible above noise.Also visible is the Clock Induced Charge (CIC) which is the dominant noise source (typical value 0.03e-)
0
1
2
3
4
5
6
7
8
0 10 20 30 40 50 60
Photons per pixel per f rame
SN
R
Conventional CCD 5e- noise
L3 CCD with no CIC
photon noise limit
EMCCD wins due to zero read noiseEMCCD loses due to multiplication noise
EMCCD range of operation
EMCCD
So at higher expsoure levels the EMCCD actually performs worse than a normal CCD
Raw input frames Thresholded and accumulated
Particles? Waves?
Cry
ogen
ic C
CD
87 im
agin
g a
fain
t pin
hole
Early EMCCD Demonstrations
1) Crab Nebula pulsar at 180fps
2) Photon interference in the lab
Threshold