CCDs Charge Coupled Devices

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CCDs(Charge Coupled Devices)

• An Imaging Technology in Visible Light
• Marino Maiorino - Dec. 1st 2006
• 1500 Downstairs Meeting Room

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Summary

• Introduction
• The Birth of New Technologies
• CCD Features
• Technological Limitations
• Basic Data Manipulation
• IFAE and CCDs
• Improper Applications
• Alternative Technologies
• Latest Developments

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Introduction

• On Visible and Optical Wavelengths
• Image Recording Techniques
• Transition between film and Solid-State detectors
• Digital revolution
• Astronomical Imaging With Film
• Telescopes do NOT magnify they get more light!
  Massimo Capaccioli

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On Visible and Optical Wavelengths(Introduction)

• Visible (380 750 nm)
• What is visible to the human eye
• Optical (300 1000 nm)
• Includes some UV and IR
• Range of wavelengths where optics laws apply

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Naked Eye Observation(Image Recording Techniques)

• 6 Mcones
• 200 Mrods
• Logarithmic sensor
• Daylight (Photopic) vision
• Nighttime (Scotopic) vision

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Naked Eye Observations(Image Recording
Techniques)
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Film(Image Recording Techniques)

• Allows
• Objective Measurements
• Light Integration
• Features
• Higher Quantum Eff.
• Broader Spectral Allowance

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Film(Image Recording Techniques)

• Reciprocity failure
• Exp. ? Aperture ShutterTime FilmSpeed
• The law of reciprocity golden rule of
  photography. Defines the relationship between
  shutter time, aperture, and film speed with
  respect to an exposure
• Changes to any of the latter three elements are
  done in stops. A stop is equal to a factor of 2

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Film(Image Recording Techniques)

• Unsharp Masking
• A form of photographic alchemy
• Subtract a blurred image to the original
• Enhance the local contrast

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Solid-State Detectors(Image Recording Techniques)

• An incoming photon kicks an electron in the
  conduction band
• The read-out system gives you a digital signal,
  which can be numerically processed!

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Astronomical Imaging with Film(Introduction)

• Special film or photographic plates
• A method to combat reciprocity failure is
  gas-hypering the film is soaked in a mixture of
  hydrogen and nitrogen gas at elevated
  temperatures for prolonged periods before
  exposure
• Very long exposure times (hours)
• Filtered Imaging
• Chemical Development

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The Birth of New Technologies

• CCD (Charge-Coupled Devices)
• CMOS (Complementary Metal Oxide Semiconductors)
• Comparing Technologies
• Companies Rule

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CCD (Charge-Coupled Devices) (The Birth of New
Technologies)

• Willard Boyle and George Smith, 1969, Bell Labs
• Working on the bubble memories
• Silicon is sensitive to light
• If exposed to light, one can grab images

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CCD (Charge-Coupled Devices) (The Birth of New
Technologies)

• Bucket Brigade
• Integration
• Charge Shift and Read-out

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CMOS(The Birth of New Technologies)

• Every pixel has its own charge-to-voltage
  converter
• Sensor often also includes
• Amplifiers
• Noise-correction circuitry
• Digitization circuitry
• The chip outputs digital bits
• Increased design complexity
• Reduced area for light capture
• As each pixel does its own conversion, uniformity
  is lower
• The chip can be built to require less off-chip
  circuitry for basic operation (camera on a chip)

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Film vs. CCD(Comparing Technologies)
CCD
Film

• no loss of sensitivity to light during exposure

• reciprocity failure beyond a few second exposure

• no minimal light intensity needed to detect a
  target

• minimal light intensity required to detect a
  target at all

• low quantum efficiency (max. 4 at optimal
  wavelengths)

• high efficiency of light detection (up to 90,
  though device- and wavelength-dependent)

• signal is proportional to light intensity

• response to light is non-linear

• large dynamic range (typically 16-bit)

• small dynamic range (6-bit)

• picture elements (pixels) are regularly spaced

• picture elements (grain) are randomly distributed

• ready for digital processing

• needs to be processed in a chemical darkroom

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Film vs. CCD(Comparing Technologies)

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Film vs. CCD(Comparing Technologies)
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CCD vs. CMOS(Comparing Technologies)
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Companies Rule(The Birth of New Technologies)

• Commercial Requirements (fast read-out time, high
  noise)
• (HAD) ?
• (CMOS)
• (Super CCD)

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Trichromy(Companies Rule)

• Color Filter Array (CFA), by Dr. Bryce Bayer,
  Kodak, 1970
• Where not available, color values are interpolated

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Device Shape(Companies Rule)

• Ideal shapes
• Square (easy to manufacture)
• Hexagonal (use most of focal plane area)
• Circular (use all of the focal plane area)
• Typical Width to Height factor is 43 (TV, PC
  monitors, etc.)

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(Companies Rule)

• Color Filter Array (CFA), 1970
• Transparent Gate Technology, 1998 (aka Blue Plus)
  to improve device sensitivity
• They even sell you evaluation boards, or you can
  build them on your own! http//www.kodak.com/ezpre
  s/business/ccd/global/plugins/acrobat/en/eval/Koda
  kAreaArrayCCDTimingGenerator.pdf

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(Companies Rule)

• HAD (Hole Accumulated Diode)
• Technique to reduce electronic noise by reducing
  the dark current.
• The holes created by heat or imperfections in the
  creation of the imaging chip are accumulated in a
  separate semiconductor layer that acts as a diode
  and prevents them from returning or creating
  noise.
• Microlenses layers

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-(Companies Rule)

• Three CCDs Trichromy
• Philips trichroic beam-splitter

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(Companies Rule)

• Introducing CMOS devices with a 32 factor
  (compatible with old fashioned film)
• EOS 1Ds Mark II, 16.7 Mpxl sports a 3624mm sensor

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Fujifilm - SuperCCD(Companies Rule)
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CCD Features

• Kodak KAF-1001

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Charge Transfer Efficiency(CCD Features)

• Kodak KAF-1001 features a 10241024 image matrix
• CTE gt 0.99997 at 40 C
• If xs, ys is the horizontal/vertical position of
  a pixel in the CCD matrix, charge being read by
  the read-out amplifier is
• Qreadout QpixelCTE(xs ys)
• The farthest pixel from the amplifier loses 6 of
  its charge
• If CTE 0.999 ? loss 87!!!

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Sensitivity Improvements(CCD Features)

• Front-Illuminated CCDs
• Back Illuminated (Back-Thinned) Higher QE,
  Wider illuminated area, Semi-transparent to NIR
• Deep Depletion (deeper photoactive region)
• Electron Multiplying CCDs A gain amplifier is
  put before the output amplifier (avalanche diode)

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Technological Limitations

• Noise Sources
• CCD output stage kT/C-noise
• Semiconductor Noise Shot, Flicker, White Noise
• Resistor / Thermal Noise
• ADC Quantization Noise
• Line Frequency, 50/60 Hz
• Blooming
• Effective Energy Resolution
• Spectral Insensitivity
• Time insensitivity

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Noise Sources(Technological Limitations)

• Blind Frame around the central sensor
• Cool the sensor (-40 C)
• Take a dark frame image and subtract it from real
  images

-

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Blooming(Technological Limitations)

• The charge generated into a pixel spills over
  to the neighbouring ones.
• At readout time, this charge can be found in the
  pixels along one column/raw
• Can be cured by introducing an anti-blooming
  drain gate

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Effective Energy Resolution(Technological
Limitations)

• The energy needed to kick an electron in the
  conduction band, in Si, is at least 1.12eV (1100
  nm, far IR)
• This is very good for far UV, X-rays and ?-rays
  (from 100 eV and beyond), but useless in visible
  (300 nm 4.1eV)
• Read-out noise ( 10 e-) limits any serious
  discussion about the topic in visible light

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Spectral Insensitivity(Technological
Limitations)

• A time-integrated image contains electrons
  generated by photons of different energies
• How to discriminate among them?

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Time Insensitivity(Technological Limitations)

• Dark subjects require long exposure times
• Time-integrated images contain electrons
  generated by photons arrived at different times
• Gamma ray bursts and other phenomena may require
  much higher time resolution

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Basic Data Manipulation

• Dark Frame Acquisition
• Flat Field Acquisition
• Image Acquisition
• Noise Subtraction
• Gain Adjustment

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Basic Data Manipulation

• For multi-band images, repeat the processing for
  any monochrome image, then stack them

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IFAE and CCDs

• DES (Dark Energy Survey)
• 500 Megapixel camera, DAQ system fast enough to
  take images in 17 seconds
• Galaxy Cluster counting - 20,000 clusters to z1
  with M gt 2x1014 M?
• Weak lensing - 300 million galaxies with shape
  measurements over 5000 sq deg.
• Spatial clustering of galaxies - 300 million
  galaxies to z 1 and beyond
• Standard Candles - 2000 SN Ia, z 0.30.8
• Multi-bandpass wide area survey, designed to
  produce photometric redshifts from 0.2 lt z lt 1.3

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g, r, i, z Photometry(IFAE and CCDs)

• Gunn griz System was originally defined in terms
  of photoelectric detectors (Thuan Gunn 1976
  Wade et al. 1979), but is now used primarily with
  CCDs
• It is defined by a few dozen standard stars
• The star BD17deg4708, an F6 subdwarf with
  B-V0.43, is defined to have colors equal to zero

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DES CCDs(IFAE and CCDs)

• 40962048 pixel
• Square pixels, 15µm size
• Resolution 0.27/pixel
• Back-thinned
• CTE lt 0.99999 (Lose at most 6)
• Noise lt 5 e-

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DES CCDs(IFAE and CCDs)
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Improper Applications

• X-ray Imagers (Astrophysics, Medicine)
• Cover the sensor with some fluorescent material
• High energy photons get absorbed and re-emit at
  lower energy
• Single-photon counting (far UV, X- and ?rays)
• Make sure that the number of photons per unit
  time is AT MOST 1 per pixel
• Take one image per unit time
• The charge measured per pixel is directly
  proportional to the incoming photon energy

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Latest Developments

• Multi-Layer Sensors
• Originally, an April fish about CANON, in 2000
• It was actually under development at FOVEON and
  released in 2002
• CMOS technology
• Principle silicon absorbs different wavelengths
  at different depths
• 100 of light, captured
• No colour interpolation needed
• Sigma, Polaroid and Hanvision products feature
  this technology

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Alternative Technologies

• Scientists want a device with
• Reasonable noise (i.e. ? Poisson limit)
• Reasonable sensitivity (i.e ? 100)
• Reasonable space resolution (i.e. ?
  diffraction limited)
• Reasonable spectral resolution (i.e. ? ?E/E lt
  0.1)
• Reasonable time resolution (i.e. ? 0 ps)

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Bibliography Web References

• http//aberrator.astronomy.net/moon/index.html
• http//ncmi.bcm.tmc.edu/ncmi/events/workshops/work
  shops_53/proceeding/2005July26_DetectingElectronsL
  ecture.ppt
• http//home.earthlink.net/kitathome/LunarLight/mo
  onlight_gallery/technique/reciprocity.htm
• http//www.lumigen.com/documents/CL_measure.shtml
• http//www.olympusfluoview.com/theory/detectorsint
  ro.html
• http//angryastronomer.blogspot.com/2006/06/astron
  omical-data-2b-light-detection.html
• http//www.fvastro.org/presentations/ImagingFilm/I
  maging20with20Film.pdf
• http//micro.magnet.fsu.edu/primer/digitalimaging/
  concepts/concepts.html
• http//www.astrosurf.com/jwisn/deepsky.htm
• http//en.wikipedia.org/wiki/Science_of_photograph
  y

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Bibliography Web References

• http//www.avaloninst.com/content/raman_informatio
  n/glossary.htm
• http//fy.chalmers.se/astro/master/vl/lp1/photfilt
  ers.pdf
• http//www.cs.wisc.edu/graphics/Courses/559-s2002/
  lectures/cs559-2.ppt
• http//www.kodak.com/US/en/dpq/site/SENSORS/name/I
  SSHome
• http//www.canon.com/technology/canon_tech/explana
  tion/cmos.html
• http//www.fujifilm.com/about/technology/super_ccd
  /
• http//www.fujifilm.com/news/n030122.html
• http//www.telescope-service.com/atik/start/atikst
  art.html
• http//soho.estec.esa.nl
• http//starizona.com/acb/ccd/advtheorycolor.aspx
• http//www.astrosurf.com/re/index.html

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Bibliography Web References

• http//www.foveon.com/article.php?a67
• https//www.darkenergysurvey.org/
• http//www.astro.utoronto.ca/patton/astro/mags.ht
  ml
• http//ulisse.pd.astro.it/Astro/ADPS/Systems/index
  .html
• Ron Wodaski, The New CCD Astronomy