L3 sensors

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• L3 sensors
• Red optimised CCDs
• Large format CCDs
• CMOS versus CCD
• Controller Developments
• Getting lower noise from standard detectors
• Large Mosaic projects

Nov 2005
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L3 technology
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L3 Technology
Electron multiplying CCDs for ultra low
noise. Readout noise becomes decoupled from
readout speed. 10Mpix/second at lt1e noise
Multiplication register
Store Area
Image Area
Normal Serial register
Multiplication register
1e- in
1000e- signal out
Multiplication register
Standard MOSFET amplifier
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L3 Technology
Typical bias shows single electron events
(unfortunately not all are due to photons!)
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L3 CCDs Ability to see single photons
Threshold
Cryogenic CCD87 imaging a faint pinhole
Raw input frames
Thresholded and accumulated
Particles? Waves?
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ING L3 cameras
Two L3 detectors have been incorporated into
cryogenic cameras. Both have read noise in the
0.1e region. Further details on the
Detector Group Website
QUCAM1 CCD97 QUCAM2 CCD201 512 x 512 x
16mm pixels 1024 x 1024 x 13mm pixels
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ING L3 cameras
WHT ISIS QUCAM1 used to observe IP
Pegasus (movie sequence of 5s exposures over
30minutes)
Ha
Un-eclipsed accretion disc spectra
Blue side of disc occulted
Full eclipse
Blue side of disc emerging..
Blue side of disc emerged
White dwarf with accretion disc in orbit around
larger primary star. Accretion disc luminosity
dominates and its light is highly Doppler shifted.
Red side also emerging
-500km/s
500km/s
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L3 WFS at ING
A CCD60 L3 detector will be used as a Natural
Guide star sensor for GLAS
Predicted gains from using L3 NGS sensor on
current NAOMI AO system
L3 on the WHT, May 2005
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ESO CCD-220 L3 CCD Project
ESO have also decided to invest in L3 technology
for their Planet Finder instrument. CCDs
delivered in 2007. Paid for with Opticon
money. Will combine L3 technology, Deep Depletion
silicon and Electronic Shuttering.
40 x 40 subapertures 6 x 6 pixel
windows ReadNoise 1e Frame rates gt1KHz
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Electronic Shuttering
5ms reaction time for small devices. Will be
used for ESO E2V L3 WFS in combination with
Rayleigh laser
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Electronic Shuttering
When activated, the shutter drain produces a
depletion volume that blocks pixel sensitivity.
Charge transfer during readout is unaffected.
Extinction ratios
Shutter open
Shutter closed
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Red Sensitive CCDs
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Red Sensitive CCDs
Standard thinned CCDs suffer from fringing
And poor red sensitivity
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Fringe Suppression CCD structures
New fringe suppression process available on
E2VCCDs. Each pixel has a landa/4 rebate (at
900nm) covering half its area. When combined with
Deep Depletion silicon it gives a substantial
reduction in fringing.
Electrode Structure
l/4 step
pixel boundary
pixel boundary
incoming photons
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Fringe Suppression CCD structures
Prototype device tested on ISIS Red arm. New 2k x
4k chip based on this technology is now on order
for August 2006 delivery.
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Red Response of CCDs
Approaching 1um wavelength Silicon becomes
increasingly transparent. Increasing thickness
acts to boost red QE.
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LBNL Hi-Rho CCDs for SNAP and DEC projects
Under thinned standard Si.
Electric potential
n
p
Photoelectron lost to recombination
Photoelectron detected
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LBNL Hi-Rho CCDs for SNAP and DEC projects
PSF very dependant on the backside bias potential
VSUB 5V
20V
115V
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LBNL Hi-Rho CCDs for SNAP and DEC projects
Devices are 300 microns thick so see a lot of
cosmic rays.
Red response right up to bandgap limit of
silicon. Not commercially available
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Commercial Large Format CCDs
E2V device will be priced to be slightly
less than two 2k x 4k devices of the same
area. E2V will also offer 15mm pixel variant.
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New Controller Developments
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Controller Developments
SDSU controller board set
Field Programmable Gate Arrays make things
simpler Controller on a board
Video processor ADC
Clock Drivers
Shutter, Thermal Control
ESO Next Generation controller and its PCi
interface card.
Sequencer, Fibre comms
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New ESO controller
2.5Gb/s fibre link Complete 4 channel CCD
controller 10W power consumption
Clocks/Biases
Xilinx Virtex II Pro FPGA Contains Comms Data
Transfer Sequencer Telemetry Glue Logic
Video Processor/ADC
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More on FPGAs
VirtexII-pro hardware contains 2x 300MHz Power
PCs hard cores Up tp 20 3 GB/s serial
transceivers Up to 8MBits of RAM Up to 444 18 bit
multipliers Up to 100K configurable logic
cells Logic cells can be combined at
programming to form powerful logical elements
950 logic cells a 150MHz 32 bit DSP This is
the future of CCD controller technology. In-contr
oller applications can be implemented Centroidin
g Bias subtraction Digital CDS Complex IR readout
modes Wavefront reconstruction in AO systems
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Getting lower noise from standard detectors
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Low Noise Techniques
Increasing readout time lowers the noise of a CCD
but with diminishing returns. Approximately 3-4e
noise floor is reached at 5 us per pixel.
Increasing readout time allows more time for the
signal to be sampled leading to a smaller noise
bandwidth and less Johnson noise.
EEV12 noise characteristics
Charge dump
Reference level
Signal level
1 Pixel
CCD raw output
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Traditional CDS method
Analogue processing of waveform followed by a
single ADC sample of the result
Charge dump onto output node
OD
RD
R
SW
Reset Transistor
Output Node
Summing Well
Output Transistor
OS
-1
Output amplifier of CCD
CDS Correlated Double Sampling
ADC
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Low Noise Techniques
By examining noise spectrum of a CCD amplifier we
can see why 1/f or flicker noise.
Video amplifier bandwidths shown below for two
pixel speeds. They see the 1/f noise.
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Traditional CDS Failings
Video waveform with low frequency noise component
superimposed
Charge dump onto output node
So when 1/f noise is significant, the information
content of the signal is higher close to the
charge dump
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Digital CDS Alternative
Connect ADC direct to front end amplifier
OD
RD
R
SW
Multiple samples per pixel Fast ADC
Reset Transistor
Output Node
Summing Well
Output Transistor
Digitally Process the waveform
OS
ADC
Output amplifier of CCD
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Digital CDS Alternative
Signal samples
From paper by Jean-Luc Gach , Laboratoire
dAstrophysique, Marseille
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Digital CDS Alternative
Optimised filter coefficients gave further
improvement
With E2V CCD using this filter shape the readout
noise was reduced from 5e to 1.7e.
It should be noted that this technique still
requires extended readout times
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SDSU Controller Experiments
The hardware exists to implement Digital CDS on
SDSU controllers
Drop-in 10MHz 14bit ADC for SDSU Video Processor
Card
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CCDs versus CMOS
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CCD Versus CMOS
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CMOS Sensitivity
Thin depletion region means low red
sensitivity. If depletion depth could be
increased, CMOS will start to look very
attractive.
Sony 12.84 Mpixel CMOS sensor
Microlenses solve fill factor problem
photodiode
transistors
CMOS pixel structure
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Hybrid CMOS
Solution is hybridisation Silicon multiplexer
bump bonded to Silicon absorber CCD-like QE
all the advantages of CMOS However, still very
expensive, CCDs still have the upper hand.
Rockwell HySiVi 4k x 4k detector
For blank-cheque applications. May be used for
LSST where 15 second exposures must be read out
in 1-2 seconds
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Large CCD Mosaics
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Large Mosaic Projects
INTWFC
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ESO OmegaCam
256 Megapixel
For VLT Survey Telescope. Camera ready for use.
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MMT MegaCam

• 36 2048x4608 13.5micron pixels
• 200kps through 72 amplifiers
• 2 additional ccd42-90s for guiding/focus
• Currently in use.

340 Megapixel
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CFHT MegaCam

• 40 2048x4608 pixel CCDs
• 1 square degree field
• Commissioned Jan 2003

360 Megapixel
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Supernovae Acceleration Probe (SNAP)
440MegaPixel
1.8m space based telescope. 2009

• 3.5k x 3.5k CCDs
• similarly sized IR array

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CTIO Dark Energy Camera
62 2k x 4k CCDs. To be commissioned 2009 CCDs
are extra thick red sensitive CCDs Originally
developed at LBNL for the SNAP spacecraft
500 Megapixel
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PanSTARRS

• X 5k square Orthogonal Transfer CCDs
• Four cameras to be built.
• First camera/telescope ready in 2006-2008

1.4GigaPixel
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PanSTARRS Orthogonal transfer CCDs
During integration, charge can be shuffled around
the chip to perform Tip-Tilt correction
Orthogonal transfer CCD pixel
OT tracking (0.50)
Normal guiding (0.73)
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1.5GigaPixel
Comparable size to detectors required for the
proposed ESO OWL 100m telescope. 2011 Launch
170 CCDs14MEuros
Palomar Schmidt Plate size comparison
Gaia Optics
1.4 ? 0.5 m mirrors
Gaia Focal Plane
CCDs
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Large Synoptic Survey Telescope
3GigaPixel
Will survey whole available sky every 3 nights.
8.4m primary 200 x 4k x 4k Detectors 3.5 degree
field of view 20-30 TByte per night 2 second
mosaic readout. May require hybrid detector
technology
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End of presentation