1. IMAGE SENSORS
Guided By: Submitted By:
Dr. M.A. Ansari Pranav Haldar (40)
Assistant Professor Sumit Srivastava (52)
Dept. of Electrical and Electronics Engineering EN 3rd Year

2. Contents
 What is a Sensor?
 How to choose a sensor?
 Types of Sensors
 What is an Image Sensor?
 What is a Pixel?
 What is Fill Factor?
 Image Sensor History
 Types of Image Sensors
 History of CCD
 History of CMOS
 What is CCD?
 Basic Operation of a CCD
 What is CMOS?
 Basic Operation of a CMOS
 CCD vs CMOS
 Applications of Image Sensors
 Conclusion

3. What is a Sensor?
 A sensor is a device that measures a physical
quantity and converts it into a signal which can be
read by an observer or by an instrument.
 For example, a thermocouple converts temperature
to an output voltage which can be read by a
voltmeter.
 For accuracy, all sensors need to be calibrated
against known standards.

4. How to choose a sensor?
 Environment: There are many sensors that work well
and predictably inside, but that choke and die
outdoors.
 Range: Most sensors work best over a certain range of
distances. If something comes too close, they bottom
out, and if something is too far, they cannot detect it.
Thus we must choose a sensor that will detect
obstacles in the range we need.
 Field of View: Depending upon what we are doing, we
may want sensors that have a wider cone of detection.
A wider “field of view” will cause more objects to be
detected per sensor, but it also will give less
information about where exactly an object is when one
is detected.

5. Types of Sensors
 Thermal Energy Sensors
 Electromagnetic Sensors
 Mechanical Sensors
 Chemical Sensors
 Optical and Radiation Sensors
 Acoustic Sensors
 Biological Sensors

6. Thermal Energy Sensors
 Temperature Sensors:
Thermometers, Thermocouples, Thermistors, Bi-
metal thermometers and Thermostats.
 Heat Sensors:
Bolometer, Calorimeter.

7. Electromagnetic Sensors
 Electrical Resistance Sensors:
Ohmmeter, Multimeter
 Electrical Current Sensors:
Galvanometer, Ammeter
 Electrical Voltage Sensors:
Leaf Electroscope, Voltmeter
 Electrical Power Sensors:
Watt-hour Meters
 Magnetism Sensors:
Magnetic Compass, Fluxgate Compass, Magnetometer, Hall
Effect Device

8. Mechanical Sensors
 Pressure Sensors:
Altimeter, Barometer, Barograph, Pressure Gauge, Air
Speed Indicator, Rate of Climb Indicator, Variometer.
 Gas and Liquid Flow Sensors:
Flow Sensor, Anemometer, Flow Meter, Gas Meter,
Water Meter, Mass Flow Sensor.
 Mechanical Sensors:
Acceleration Sensor, Position Sensor, Selsyn, Switch,
Strain Gauge.

9. Chemical Sensors
 Chemical sensors detect the presence of specific
chemicals or classes of chemicals.
 Examples include oxygen sensors, ion-selective
electrodes, pH glass electrodes, redox electrodes.

10. Optical and Radiation Sensors
 Radiation Sensors:
Geiger Counter, Dosimeter, Scintillation Counter.
 Proximity Sensor.
 Scanning laser.
 Interferometry.

11. Acoustic Sensors
 Microphone.
 Hydrophones.
 Seismometers.

12. Biological Sensors
 All living organisms contain biological sensors with
functions similar to those of the mechanical devices
described.
 These include our eyes, skin, ears and many more.

13. What is an Image Sensor?
 Unlike traditional camera, that use film to capture
and store an image, digital cameras use solid-state
device called image sensor.
 Image sensors contain millions of photosensitive
diodes known as photosites.
 When you take a picture, the camera's shutter
opens briefly and each photo site on the image
sensor records the brightness of the light that falls
on it by accumulating photons. The more light that
hits a photo site, the more photons it records.

14.  The brightness recorded by each photosite is then
stored as a set of numbers (digital numbers) that
can then be used to set the color and brightness of
a single pixel on the screen or ink on the printed
page to reconstruct the image.

15. What is a Pixel?
 The smallest discrete component of an image or
picture on a CRT screen is known as a pixel.
 “The greater the number of pixels per inch the
greater is the resolution”.
 Each pixel is a sample of an original image, where
more samples typically provide more-accurate
representations of the original.

16. What is Fill Factor?
 Fill factor refers to the
percentage of a photosite
that is sensitive to light.
 If circuits cover 25% of each
photosite, the sensor is said
to have a fill factor of 75%.
The higher the fill factor, the
more sensitive the sensor.

17. Image Sensor History
 Before 1960 mainly film photography was done and
vacuum tubes were being used.
 From 1960-1975 early research and development
was done in the fields of CCD and CMOS.
 From 1975-1990 commercialization of CCD took
place.
 After 1990 re-emergence of CMOS took place and
amorphous Si also came into the picture.

18. Types of Image Sensors
 An image sensor is typically of two types:
3. Charged Coupled Device (CCD)
5. Complementary Metal Oxide Semiconductor
(CMOS)

19. History of CCD
 The CCD started its life as a memory device and
one could only "inject" charge into the device at an
input register.
 However, it was immediately clear that the CCD
could receive charge via the photoelectric effect and
electronic images could be created.
 By 1969, Bell researchers were able to capture
images with simple linear devices; thus the CCD
was born.
 It was conceived in 1970 at Bell Labs.

20. History of CMOS
 Complementary metal–oxide–semiconductor
(CMOS), is a major class of integrated circuits.
CMOS technology is used in microprocessors,
microcontrollers, static RAM, and other digital logic
circuits.
 CMOS technology is also used for a wide variety of
analog circuits such as image sensors, data
converters, and highly integrated transceivers for
many types of communication. Frank Wanlass
successfully patented CMOS in 1967.

21. Charged Coupled Device (CCD)

22. What is CCD?
 Charge-coupled devices (CCDs) are silicon-based
integrated circuits consisting of a dense matrix of
photodiodes that operate by converting light energy
in the form of photons into an electronic charge.
 Electrons generated by the interaction of photons
with silicon atoms are stored in a potential well and
can subsequently be transferred across the chip
through registers and output to an amplifier.

23. Basic Operation of a CCD
 In a CCD for capturing images, there is a photoactive
region, and a transmission region made out of a shift
register (the CCD, properly speaking).
 An image is projected by a lens on the capacitor array
(the photoactive region), causing each capacitor to
accumulate an electric charge proportional to the light
intensity at that location.
 A one-dimensional array, used in cameras, captures a
single slice of the image, while a two-dimensional array,
used in video and still cameras, captures a two-
dimensional picture corresponding to the scene
projected onto the focal plane of the sensor.

24.  Once the array has been exposed to the image, a control
circuit causes each capacitor to transfer its contents to
its neighbor.
 The last capacitor in the array dumps its charge into a
charge amplifier, which converts the charge into a
voltage.
 By repeating this process, 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.

25. Transformation of an image using a CCD array
1- CCD camera, 2- CCD detector, 3- Reading, 4- Amplifier, 5- A/D converter,
6- Digitization , 7- Download

26. Types of CCD Image Sensors
1. Interline Transfer CCD Image Sensor
3. Frame Transfer CCD Image Sensor

27. Frame Transfer CCD Image Sensor
 Top CCD array used for photodetection (photogate) and
vertical shifting.
 Bottom CCD array optically shielded – used as frame
store.
 Operation is pipelined: data is shifted out via the bottom
CCDs and the horizontal CCD during integration time of
next frame.
 Transfer from top to bottom CCD arrays must be done
very quickly to minimize corruption by light, or in the dark
(using a mechanical shutter).
 Output amplifier converts charge into voltage,
determines sensor conversion gain.

28. How CCD works?
i h g Image pixel
f e d
c b a
i h g
f e d
i h g
Horizontal transport
register c b a
f e d
Vertical shift c b a Output
Horizontal shift

29. Interline Transfer vs Frame Transfer
 Frame transfer uses simpler technology (no
photodiodes), and achieves higher fill factor than
interline transfer.
 Interline transfer uses optimized photodiodes with
better spectral response than the photogates used
in frame transfer.
 In interline transfer the image is captured at the
same time (`snap shot' operation) and the charge
transfer is not subject to corruption by
photodetection (can be avoided in frame transfer
using a mechanical shutter).

30.  Frame transfer chip area (for the same number of
pixels) can be larger than interline transfer.
 Most of today’s CCD image sensors use interlines
transfer.

31. Complementary Metal Oxide Semiconductor (CMOS)

32. What is CMOS?
 “CMOS" refers to both a particular style of digital circuitry
design, and the family of processes used to implement
that circuitry on integrated circuits (chips).
 CMOS circuitry dissipates less power when static, and is
denser than other implementations having the same
functionality.
 CMOS circuits use a combination of p-type and n-type
metal–oxide–semiconductor field-effect transistors
(MOSFETs) to implement logic gates and other digital
circuits found in computers, telecommunications
equipment, and signal processing equipment.

33. Basic Operation of CMOS
 In most CMOS devices, there are several transistors at each
pixel that amplify and move the charge using wires.
 The CMOS approach is more flexible because each pixel can
be read individually.
 In a CMOS sensor, each pixel has its own charge-to-voltage
conversion, and the sensor often also includes amplifiers,
noise-correction, and digitization circuits, so that the chip
outputs digital bits.
 With each pixel doing its own conversion, uniformity is lower.

34.  As shown above, the CMOS image sensor consists of a large
pixel matrix that takes care of the registration of incoming
light.
 The electrical voltages that this matrix produces are buffered
by column-amplifiers and sent to the on-chip ADC.

35. Interline Transfer CCD Image Sensor
 Photodiodes are used.
 All CCDs are optically shielded, used only for readout.
 Collected charge is simultaneously transferred to the
vertical CCDs at the end of integration time (a new
integration period can begin right after the transfer) and
then shifted out.
 Charge transfer to vertical CCDs simultaneously resets
the photodiodes, (shuttering done electronically for `snap
shot' operation).

36. Types of CMOS Image Sensors
1. Active Pixel Image Sensor
3. Passive Pixel Image Sensor

37. Active Pixel Image Sensor
 3-4 transistors per pixel.
 Fast, higher SNR, but
 Larger pixel, lower fill factor.
 Lower voltage and lower
power.

38. Passive Pixel Image Sensor
 1 transistor per pixel.
 Small pixel, large fill factor,
but
 Slow, low signal to noise
ratio (SNR).

39. CCD vs CMOS
 CMOS image sensors can incorporate other circuits
on the same chip, eliminating the many separate
chips required for a CCD.
 This also allows additional on-chip features to be
added at little extra cost. These features include
image stabilization and image compression.
 Not only does this make the camera smaller, lighter,
and cheaper; it also requires less power so batteries
last longer.

40.  CMOS image sensors can switch modes on the fly
between still photography and video.
 CMOS sensors excel in the capture of outdoor
pictures on sunny days, they suffer in low light
conditions.
 Their sensitivity to light is decreased because part of
each photosite is covered with circuitry that filters
out noise and performs other functions.
 The percentage of a pixel devoted to collecting light
is called the pixel’s fill factor. CCDs have a 100%
fill factor but CMOS cameras have much less.

41.  The lower the fill factor, the less sensitive the sensor
is and the longer exposure times must be. Too low a
fill factor makes indoor photography without a flash
virtually impossible.
 CMOS has more complex pixel and chip whereas
CCD has a simple pixel and chip.

42. APPLICATIONS
OF
IMAGE SENSORS

43. Digital Cameras

44. Personal Digital Assistance (PDA)

45. Camcorders

46. Toys and Robots

47. Fingerprint Scanner

48. Some other applications
 Biometrics.
 Optical Mouse.
 Video Conferencing.

49. Conclusion
 Image sensors are an emergent solution for
practically every automation-focused machine-vision
application.
 New electronic fabrication processes, software
implementations, and new application fields will
dictate the growth of image-sensor technology in the
future.

50. Thank You Very Much
For Your Attention