Transcript Charged Coupled Device

Charged Coupled Device
Imaging
By
Marc Castro
17443948
CCD Imaging Process
(3 step process)
1. Exposure
Converts light into an electronic charge at discrete sites
called pixels, photo sites, photodiodes or capacitors.
2. Charge Transfer
One of the CCD architectures is used.
3. Charge to voltage
Signal conversion from analog (electrical charges)
to digital (0’s and 1’s).
How does it look like?
Charged Couple Device
What is it?
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Charged Coupled Device (CCD)
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an analog shift register, that enables the
transportation of analog signals (electric charges)
through successive stages (pixels) controlled by a
clock signal.
Primary uses:
Memory
 Delaying samples of analog signals
 In an array of photoelectric light sensors (image
sensors)
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History
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Invented in 1969
Creators: Willard Boyle and George E. Smith
 Location: AT&T Bell Labs. Currently part of Lucent
Technologies
 Motivation: the lab was working on the picture
phone and on the development of the
semiconductor bubble memory.
 CCD – originally designed as an electronic memory
device that can be charged by light.
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CCD Fabrication
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Made using photolithography techniques.
Individual pixel gate fabricated on a silicon wafer
Courtesy of Olympus
End Product
Don Groom LBNL
Capturing Images
The CCD
- comprised of many
individual signal capture
units (photo sites,
capacitors, pixels)
CDD - 2D Pixel Array
Capturing Images
How charges are stored
•CCDs are comprised of
pixels (capacitors) which
are MOS (Metal Oxide
Semiconductors).
•MOS allow electron
charges to build up within
the wells.
Capturing Images
•Light – incoming photons falls onto the
surface of a pixel.
(CDD - 2D array of pixel elements)
•Result- generates free electrons in the
silicon of the CCD due to the photoelectric
effect, proportional to the number of
photons striking it. These electrons collect in
little packets.
•Point- the total charge is proportional to the
light intensity at that pixel.
A brighter image ( higher electrical charge).
A darker image ( lower electrical charge).
•Drawback- only measures intensity.
Not color!!!
•CCD’s normally have 1 to 5 million packets
of charge.
CCD Scanning Formats
CCDs can be used to collect an image in one
of three ways, either one pixel at a time, one
row at a time, or as an entire area at once.
Methods to capture color
Method 1: Beam Splitter
Method 2: Bayer Pattern
Courtesy of HowStuffWorks
2-D Pixel Array with Bayer Pattern
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Used over the CCD (color grid over imaging array)
Each square (4 pixels) contains
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One red
One blue
Two green
Transfer image from array.
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General Idea –
Control circuit causes each pixel to transfer its
contents to its neighbor using a clocking scheme.
The last pixel in the array dumps its charge into a
charge amplifier, which converts the charge into a
voltage.
 The controlling circuit converts the entire
semiconductor contents of the array to a sequence
of voltages, which it samples, digitizes and stores in
some form of memory.
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Readout Architecture
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Full Frame
Frame Transfer
Interline
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They are the most common
Full Frame Architecture
Courtesy of Molecular Expressions
Frame Transfer Architecture
Courtesy of Molecular Expressions
Interline Architecture
Courtesy of Molecular Expressions
Storing the image
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Analog to digital converter
Samples the analog signal and turns the information
into bytes of (1’s and 0’s).
 Charge amplifier – converts the charge into voltage.
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Record bytes in a storage medium
Memory Cards
 Hard Drive
 DVD
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Applications
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Digital Photography
Astronomy
Sensors
Electron Microscopy
Medical Fluoroscopy
Optical and UV Spectroscopy
Devices
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Astronomical Telescopes
Scanners
Bar code readers
Machine vision for robots.
Optical character recognition (OCR)
Works Cited
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Tom Harris. “How Camcorders Work.”
HowStuffWorks.http://electronics.howstuffworks.com/camcorder.html
“Charge-coupled device.” Wikipedia. http://en.wikipedia.org/wiki/Chargecoupled_device
“Building A Charge-Coupled Device.” Olympus Microscopy Resource Center.
http://www.olympusmicro.com/primer/java/photomicrography/ccd
Tom Thompson. “Charge-Coupled Device.” ComputerWorld.
http://www.computerworld.com/softwaretopics/software/multimedia
“What is a Charge-Coupled Device.” Tech-Faq. http://www.tech-faq.com/chargecoupled-deivce.shtml
Lucent Technologies. “CCD-The History of CCDs or Charge Coupled Devices.”
About.com Inventors. http://inventors.about.com/od/cstartinventions/a/CCD.html
“Charge-Coupled Device (CCD) sensor.” MIR.
http://www/mir/com.my/rb/photography/digitalimaging/ccd/html
“Charge-coupled deivce.” Whatis.com.
http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci295633
Works Cited
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“Anatomy of a Charge-Coupled Device.” Molecular Expressions Optical Microscopy
Primer: Digital Imaging in Optical Microscopy.
http://micro.magnet.fsu.edu/primer/digitalimaging/concepts
Eric Meisenzahl. “Charge-Coupled Device Image Sensors.” Eastman Kodak Co.
http://engage.advanstar.com/jnserver/acc_random
“Charge-couple device.” Answers.com. http://www.answers.com/topic/chargecoupled-device