CCD (Charge Coupled Device)

Anatomy of Digital Camera

1. Charge Coupled
Device (CCD)
Prepared By: Sagar Reddy
DOEACC B Level ([email protected])

2. Contents
What is CCD ?
Applications
Components of CCD cameras
Types of CCDs
Advantages of CCD cameras
Summary

3. What is CCD ?
A charge-coupled device (CCD) is a sensor
for recording images in digital cameras.
It consist an integrated circuit containing an
array of linked, or coupled, capacitors acting as
many small pixels .
The light falling on a pixel is converted into a
charge pulse which is then measured by the
CCD electronics and represented by a number.
The number usually ranges from 0 (no light) to
65,535 (very intense light).

4. A CCD chip

5. Applications
CCDs are used in digital cameras, optical
scanners and video cameras as light-sensing
devices.
CCD cameras used in astrophotography.
CCDs are typically sensitive to infrared light,
which allows infrared photography, night-vision
devices, and zero lux (or near zero lux) video-
recording/photography.
CCD are use to take exposures of galaxies and
nebulae,.

6. Applications
They commonly respond to 70% of the
Incident light (meaning a quantum
efficiency of about 70%,) making them
more efficient than photographic film,
which captures only about 2% of the
incident light. As a result CCDs were
rapidly adopted by astronomers

7. CCD Camera
CCD camera mounted on telescope

8. Components of CCD
cameras
The CCD camera consists of three
main parts.
Camera body
CCD chip
Electronics

9. Camera body
The camera body is the mechanical part of the
camera. It houses the CCD chip and protects it
against unwanted light from outside. Some
CCD cameras can also be mounted on the
telescope.

10. CCD chip
A CCD (Charge Coupled Device) chip is
a light sensitive device, made of silicon.
It is an array of light sensitive pixels.
When light falls on a pixel, it will be
converted to a charge. This charge is
captured in the pixel. It can’t go to other
pixels. The more light falls on the pixel,
the more charge will accumulate in the
pixel.
The amount of charge is a measure of
the amount of light that felt on the pixel.

11. The CCD chip seen in the
camera.
CCD Chip
inside the
camera

12. an image of a
TC245 CCD
chip
representation of a small part of the light
sensitive surface of the CCD chip. You
can see it's made out of pixels

13. How a CCD chip registers
image?
The telescope projects an image on the
CCD chip. High intensity areas will
produce more charge in the pixels than
low intensity areas.
The amount of charge in every pixel
makes the image.The computer can
read this charge and convert it to an
image.

14. The value in
every pixel
gives the
charge, which
is related to
the light
intensity.

15. How is an image made with
a CCD chip?
There are three main phases:
Clearing phase
Exposure or integration phase
Readout phase

16. 1) Clearing phase
Mostly you don’t have a shutter in your camera,
this means that there is always light falling on the
CCD chip.
When you want to make an image, all existing
charge has to be removed from the pixels. The
CCD chip can shift lines downward with electrical
pulses.
All charge in a line will move to the line below of it.
This happens with all lines of the chip on the same
moment.

17. Clearing phase
The lowest line will move the charge to a
clearing line, where it will be removed.
When all lines are shifted away, there is
no charge left anymore. This phase
takes a few ms.

18. Clearing phase
Charge clearing

19. 2) Exposure or integration phase
The telescope projects the image on the CCD chip, so
charge will accumulate in the pixels.

The longer you wait, the more light will be registered by
the chip.
This phase controls the exposure time, also called:
integration time,
because the chip integrates the amount of light in a
certain period. With lunar and planetary photography it
usually takes a few tenths of a second, but it can take
minutes or even hours

20. The CCD array after 1 and 2 seconds
exposure. The charge in the pixels
accumulated with a factor of two.

21. 3) Readout phase
To get the image in your computer, it will have
to read the amount of charge of every pixel.
There is a device, the charge detection node,
in the CCD chip that is able to measure the
charge of a pixel.
Every pixel must be shifted in this device. The
lowest line is able to shift pixels to the left in the
direction of the device. So these pixels can be
measured one by one.

22. Readout phase
When all pixels of the line are measured, all
lines are shifted one line down.
Then again the lowest line can be measured.
This will be repeated until all lines are
measured.
The computer can read the measurements
through the camera electronics. This phase can
take a few seconds.

23. When the computer has collected all
measurements, it can show an image of it.

24. Electronics
The electronics of the camera are the
intermediate between the CCD chip and the
computer.
The computer must be able to control the
camera through its electronics.
To shift the lines on the CCD chip, it needs
clock signals or pulses.
They must be generated by the electronics or,
by the computer.

25. Electronics
Another important task is the conversion
of the analog output signal of the charge
detection node to a digital format the
computer is able to read.
The conversion is done by an ADC
(Analog to Digital Converter) and takes
most time of readout phase.

26. Electronics
The CB245 camera needs two electronic units.
The preamplifier
This unit is mounted on the camera body. It
amplifies the analog signal from the CCD chip and
converts the clock signals.
The interface card
This unit connects the computer to the preamplifier.
It converts the computer signals and also the
analog signal from the CCD chip to a digital format.

27. Electronics
interface card
camera and
preamplifier

28. Software
The software on the computer lets you control
the camera.
This is called the acquisition software.
You don’t have to worry about clock signals,
conversions, clearing and so on, the software
handles it.
You only have to tell the software when and
how long it has to make an image.
It also gives you the possibility to save an
image to the hard disk, for later use.

29. acquisition software (Astro -Snap)

30. The most used types of CCD
chips
Full frame device
This is the most simple device. It is used in the
CB211 camera. This type can’t be used with
lunar and planetary photography without a
shutter. Making images of this kind of objects
typically requires an integration time of a few
tenths of a second. The problem is the readout
time, which can take a few seconds. During
readout, the chip is still receiving light, which
will destroy the original image, before it’s
completely read by the computer.

31. The most used types of CCD
chips
Frame transfer device
With this kind of chip, the lowest half of the chip
is protected against light. The image is only
made on the upper half of the chip. When you
are finished making your image, the image will
be transferred from the upper half to the lower
half, where it will be protected from light. This
will take only a few ms. There is enough time, in
this area, to read the image. A frame transfer
device can be used with lunar and planetary
photography.

32. Frame transfer device
The TC245 is divided in 2 parts.

33. The most used types of CCD
chips
Interline transfer device
One line of every two lines is protected from
light. During integration, only one line receives
light. At the end, this line is shifted to the
protected line, where it will be read by the
computer. An interline transfer device can be
used with planetary photography, Lunar
photography will be more difficult, because of
it’s brightness. The bright light can influence the
protected line. The protected area of a frame
transfer device is safer.

34. intensified charged-coupled
device (ICCD)
is a CCD that is fiber-optically connected to a
micro-channel plate (MCP) to increase the
sensitivity.
In ICCD Cameras a photo-cathode in front of
the MCP converts photons to electrons which
are multiplied by the MCP.
After the MCP a phosphor screen converts the
electrons back to photons which are fiber-
optically guided to the CCD.

35. intensified charged-coupled
device (ICCD)
ICCDs are used in night vision
equipment.
Besides the gain in sensitivity the
possibility of getting the MCP also offers
the possibility to gate ICCD cameras
very fast.

36. Advantages of CCD cameras
Instant review of pictures, with no wait for the
film to be developed
If there's a problem with a picture, the
photographer can immediately correct the
problem and take another picture.
Only successful pictures need to be printed.
This means you can take many shots of the
same scene but with slightly different settings,
then choose the best one. Doing this with film
would be too expensive

37. Advantages of CCD cameras
Minimal ongoing costs for those wishing
to capture hundreds of photographs for
digital uses, such as computer storage
and e-mailing, but not printing.
Images may be copied from one media
to another without any degradation.
Digital cameras can be much smaller
than film cameras of equivalent quality.

38. Advantages of CCD cameras
Ability to capture and store hundreds of
photographs on the same media device within
the digital camera; by contrast, a film camera
would require regular changing of film (after
say, every 24 or 27 shots).
Digital image files can be backed up to CD-
ROM or DVD-ROM
Immediate image review and removal, lighting
and composition can be assessed without
wasting storage space.

39. Summary
a brief review of what happens in a CCD camera,
from beginning to end:
You aim the camera at the subject and adjust
the optical zoom to get closer or farther away.
When you press lightly on the shutter release.
The camera automatically focuses on the
subject and takes a reading of the available
light.

40. The camera sets the aperture and shutter
speed for optimal exposure.
You press the shutter release all the way.
The camera resets the CCD and exposes it to
the light, building up an electrical charge, until
the shutter closes.
The ADC measures the charge and creates a
digital signal that represents the values of the
charge at each pixel.

41. A processor interpolates the data from the
different pixels to create natural color. On many
cameras, it is possible to see the output on the
LCD at this stage.
 A processor may perform a preset level of
compression on the data.
The information is stored in some form of
memory device (probably a Flash Memory
card).

42. Memory device
Flash Memory
card
A memory stick

43. Micro-channel plate
A micro-channel plate is a device which
intensifies radiation or particles by multiplication
of electrons in small channels under the
presence of a high electric field.
Electrons which travel inside these channels
scatter frequently with the channel walls
producing more and more secondary electrons.
This process amplifies the original signal by
several orders of magnitude depending on the
electric field strength and the geometry of the
micro-channel plate.