This presentation discusses diode-based sensors. It begins by defining sensors as devices that detect inputs from the environment and output a human-readable signal. It then discusses the basic components and workings of sensors, distinguishing between analog and digital sensors. Regarding analog sensors, it provides examples like temperature, pressure, and light sensors. For digital sensors, it notes they output discrete binary values. The presentation then focuses on applications of diodes in light and temperature sensing. It describes photodiodes, phototransistors, and how they can be used in light sensors. It also explains how peltier diodes and pn-junctions can act as temperature sensors by changing voltage with temperature.

1. Presentation for
ANALOG ELECTRONICS
By: Ayesha Anum & Marwa Batool
(F20BPHY002, F20BPHY005)
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2. Diode-based sensors

3. What are sensors?
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4. “
“A sensor is a device that detects and
responds to some type of input from the
physical environment.”
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5. Input:
The input could be light, heat,
motion, moisture, pressure, etc.
Output:
The output is a signal that is
converted to a human-readable
display at the sensor location.
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◉ Most sensors are electronic but
some are simpler like glass
thermometer that presents visual
data.
◉ People use sensors to measure
temperature, gauge distance,
detect smoke, regulate pressure,
and a myriad of other uses.
Sensors
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6. How do sensors work?
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7. ◉ A sensor converts the physical
action to be measured into an
electrical equivalent.
◉ It processes the electrical signals
to be easily sent and further
processed.
◉ The sensor can output whether
an object is present or not
present (binary) or what
measurement value has been
reached (analog or digital).
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◉ A sensor is a chip that observes the
changes happening in the physical
world.
◉ It sends feedback to the
microcontroller.
◉ Excitation and grounding must be
provided to the sensor for proper
working
Working of sensors
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8. Components of sensors:
1. The sensing section contains
the sensor itself which is based
on a particular technology.
2. The processing circuitry
converts the physical variable
into an electrical variable.
3. The signal output contains the
electronics connected to a
control system.
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Types of sensors:
Micro-controller accepts two types
of inputs depending on the type of
sensor i.e., analog, or digital.
• Analog Sensors
• Digital Sensors
Components & types of sensors
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9. Analog Sensors
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10. “
“Analog sensors convert physical data
into analog signals.
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11. ◉ Analog sensors are much more
precise than digital sensors,
◉ Many types of sensors produce
continuous analog output signals
and these sensors are analog.
◉ This continuous output signal
produced by the analog sensors
is proportional to the measure.
◉ As analog signals are continuous,
they can account for changes in
the physical variable like
temperature or pressure.
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Applications of analog sensors:
◉ Accelerometers
◉ Pressure Sensors,
◉ Light Sensors,
◉ Sound Sensors,
◉ Temperature Sensors
Analog sensors
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12. Digital Sensors
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13. “
“In digital sensors, the signal measured
is directly converted into digital signal
output inside the digital sensor itself.”
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14. ◉ The digital signal is transmitted
through cable digitally.
◉ They produce discrete values (0
and 1’s).
◉ Discrete values are often called
digital or binary signals in digital
communication.
◉ Electronic sensors in which data
conversion and data
transmission take place digitally
are digital sensors.
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Types of digital sensors:
◉ Digital Accelerometers Sensors
◉ Digital Temperature Sensors
◉ Digital Humidity Sensors
Digital sensors
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15. Application of diodes in
sensors

16. 1. LIGHT SENSORS
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17. “A light sensor is a photoelectric
device that converts light energy
(photons) detected to electrical
energy (electrons).”
◉ Light sensors are a type of
photo-detector that detect light.
◉ Different types of light sensors
can be used to measure
illuminance.
◉ They respond to changes in the
amount of light received, or
convert light to electricity.
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Types of light sensors:
There are different types of light
sensors available; mainly they
include:
1. Photo-resistors
2. Photodiodes
3. Phototransistors
Light sensors
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18. a) Photodiodes
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19. “
“A photodiode is a semiconductor p–n
junction device that converts light into
an electrical current.”
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20. What are they made of?
◉ Photodiodes are mainly made
from silicon and germanium
materials.
◉ They comprise optical filters,
built-in lenses, and surface areas
How do photodiodes work?
◉ Photodiodes work on the
working principle called the
inner photoelectric effect.
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◉ When a beam of light hits,
electrons are loosened, causing
electron holes.
◉ It results in the electrical current
flowing through.
◉ The brighter the light present,
the stronger the electrical
current will be.
Photodiodes
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21. Construction:
◉ The construction of the
Photodiode light sensor is similar
to that of a PN-junction diode
◉ The diode’s outer casing is either
transparent or has a clear lens to
focus the light onto the PN
junction for increased sensitivity.
◉ The junction will respond to light
particularly longer wavelengths
such as red and infra-red rather
than visible light.
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Advantage:
◉ One main advantage of
photodiodes when used as light
sensors is their fast response to
changes in the light level.
Disadvantage:
◉ One disadvantage of this type of
photo device is the relatively
small current flow even when
fully lit.
Photodiodes
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22. b) Phototransistors
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23. “
“An electronic switching & current
amplification component which relies
on exposure of light to operate.”
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24. What are they made of?
◉ Ancient phototransistors used
single semiconductor materials
like silicon and germanium
◉ Modern components use
materials like gallium and
arsenide for high-efficiency
levels
How do photo-transisters work?
◉ The working is similar to a
photodiode including an
amplifying transistor
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◉ The light falls on the base
terminal of a phototransistor
◉ It will induce a little current then
the current is amplified through
the action of a normal transistor.
◉ The results will be extensively
large.
Phototransistors
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25. Construction:
◉ Phototransistors consist of a
bipolar NPN Transistor with its
large base region electrically
unconnected.
◉ Some phototransistors allow a
base connection to control the
sensitivity.
◉ This uses photons of light to
generate a base current.
◉ This causes a ‘collector to
emitter’ current to flow
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◉ Most phototransistors are NPN
types whose outer casing is
either transparent or has a clear
lens to focus the light onto the
base junction for increased
sensitivity.
Phototransistors
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26. Construction:
◉ In the NPN transistor, the
collector is biased positively to
the emitter so that the base
junction is reverse biased.
◉ With no light on the junction
normal leakage or dark current
flows which is very small.
◉ When light falls on the base
more electron/hole pairs are
formed in this region and the
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current produced by this action is
amplified by the transistor.
◉ Usually, the sensitivity of a
phototransistor is a function of
the DC gain of the transistor.
Phototransistors
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27. Applications of phototransistors:
Phototransistors are widely used
in different electronic devices for
detecting light:
infrared receivers, smoke
detectors, lasers, CD players, etc.
Typical applications of
Phototransistors light sensors are
in :
Optoisolators, slotted Opto
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switches, light beam sensors, fiber
optics, TV-type remote controls,
etc.
Phototransistors
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28. 2) Temperature Sensors
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29. “
“An electronic device that measures the
temperature of its environment and
converts the input data into electronic
data.”
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30. ◉ As a Temperature Sensor, the forward
current of the diode depends on the
temperature.
◉ If the forward voltage remains constant,
the increase in the temperature
decreases the forward current.
◉ It can be used to sense the temperature.
◉ Peltier or thermal diode is used for heat
monitoring in microprocessors
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Temperature sensors
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31. a) Peltier or thermal diode as the temperature
sensor
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32. “
“A Peltier diode is a diode that allows the
unidirectional flow of heat.”
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33. ◉ A thermal diode is a device
whose thermal resistance is
different for heat flow in one
direction than the other.
◉ When its first terminal is hotter
than the second terminal, heat
will flow effortlessly from the
first to the second terminal.
◉ When the second terminal is
hotter than the first terminal,
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little heat will flow from the second
terminal to the first terminal.
◉ Nowadays it is used in very large
quantities
◉ It is a single port of diode.
◉ It is issued for 2 main purposes:
1. making electricity.
2. for getting its work done.
Peltier diode
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34. b) pn-Junction as a temperature sensor
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35. ◉ Dedicated diodes and PN
junctions are commonly used as
temperature sensors.
◉ But ESD and input protection
diodes can also be used to
measure temperature.
◉ The principle of using a diode as
a temperature sensor is
straightforward.
◉ With a constant current applied,
the voltage across a diode or PN
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junction will decrease by
approximately 1 to 2 mV/°C over
temperature.
◉ The voltage change over
temperature can be used with a
lookup table or an equation to
calculate a temperature for any
given diode voltage.
◉ In this case, the die temperature
of a high-speed op-amp can be
determined.
pn-Junction as a temperature sensor
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36. Thank You
For watching!
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