radiation detectors and instrumentation - electronics
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Dr. ISMAYIL
Assistant Professor
Department of PhysicsManipal Institute of Technology
RADIATION PHYSICS(Open Elective for B.E - VI Semester)
(PHY 322)
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Dr. ISMAYIL
Assistant ProfessorDepartment of Physics
Manipal Institute of Technology
Manipal University
Academic Block-2 Basement,
Near AC Seminar Hall
E-mail:ismayil.mit@manipal.edu
Mobile Number: 98454 975462
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yllabus
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Radiation Detectors and
Instrumentation [16 hours]
Semiconductors diodes JFET
MOSFET
Integrated Circuits
OPAMP and their characteristics
Differential Amplifier
Operational amplifier systems
Pulse Amplifiers.
Ref:
Robert L Boylestad, Electronic Devices and Circuit theory
Radiation Detection and Measurement Glenn F Knoll
Measurement and Detection of radiation - NicholasTsoulfanidis
Proportional counters
GM counters Scintillation detectors
Semiconductor detectors
Thermo luminescent
Dosimeters
Radiation spectroscopy with
scintillators
Gamma spectroscopy
Multichannel pulse analyzer
Slow neutron detectionmethods
Reactor instrumentation
Principles of radiation detection
and measurements
Gas filled detectors
Ionization chambers
Theory and design
Gas multiplication
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Radiation Detectors and Instrumentation
Semiconductors diodes :
pn-junction is formed when a
p-type semiconductor is joinedto an n-type semiconductor.
A pn-junction has three distinct
regions: a p-region, an n-region,
and a depletion region at the
junction [Figure (a)].
The depletion region has no
movable charges (conduction
electrons and holes) because the
conduction electrons on the n-side
have crossed the junction due to
diffusion and neutralized the
holes on the p-side.
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Because of the fixed ion cores in the depletion region, an
electric field exists [Figure (b)], due to which there is a
potential difference Vo across the
junction [Figure (c)].
In the forward bias, the
p-side of the junction is made
positive with respect to the n-side, by application of an
external voltage V. Then the
internal potential difference Vo
across the junction decreases.
This gives rise to a current I
which increases exponentially
with the increase in forward
bias V.
CHARACTERISTIC
CURVE OF A pn-JUNCTION
REVERSE
BIAS
FORWARD
BIAS
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FORWARD BIAS :
REVERSE BIAS :
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Problem 3.1: The current in a diode under forward bias of
100 mV is 200 mA at a temperature of 300 K. What is the
current in the diode if it is under reverse bias of 100 mV ?
Solution:
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Bipolar Junction Transistors (BJT) :
The transistor is a three-layer semiconductor device
consisting of either two n-type and one p-type layers ofmaterial (npn transistor) OR two p-type and one n-type
layers of material (pnp transistor).
There are three terminal namely Emitter, Base and
Collector.
The emitter layer is heavily doped, the base lightly doped,
and the collector also lightly doped. The outer layers have
widths much greater than the sandwichedp-type or n-type
material.
Bipolar junction transistors are so named because their
operation involves both electrons and holes.
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In 1947 three American scientists named William
Shockley, John Bardeen and Walter Brattain at Bell Labs,
announced the creation of the first transistor.
The name transistor is a combination of the words
transfer and resistor - a transfer resistor - a transistor.
When it was announced the name was explained;
"because it is a resistor or semiconductor device whichcan amplify electrical signals as they are transferred
through it from input to output terminals."
This, the very first transistor was called a point-contacttransistor.
Shockley, Bardeen and Brattain received the Nobel Prize
in Physics 1956 "for their researches on semiconductors
and their discovery of the transistor effect."
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Input Characteristics Output Characteristics
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16BJTis a current-controlled device
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Field-Effect Transistors (FET) :
The field-effect transistor (FET) is a three-terminal device
used for a variety of applications that match, to a largeextent, those of the Bipolar Junction Transistors (BJT).
The primary difference between the two types of
transistors is the fact that the BJT is a current-controlled
device, while the FETis a voltage-controlled device.
Just as there are npn andpnp bipolar transistors, there are
n-channel andp-channelfield-effect transistors.
The BJT is a bipolar device i.e., the conduction level is afunction of two charge carriers, electrons and holes.
The FET is a unipolar device depending solely on either
electron (n-channel) or hole (p-channel) conduction.
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Current Controlled vsVoltage Controlled Devices
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Two types of FETs are:
Junction Field-Effect Transistor (JFET)
Metal-Oxide-Semiconductor Field-Effect Transistor
(MOSFET)
The MOSFET transistor has become one of the most
important devices used in the design and construction of
integrated circuits for digital computers.
Its thermal stability and other general characteristics
make it extremely popular in computer circuit design.
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Junction Field-Effect Transistor (JFET)
JFET is a three-terminal device
with one terminal capable of
controlling the current between
the other two.
Note that the major part of the
structure is the n-type material
that forms the channel between
the embedded layers of p-type
material.BJT FET
Emitter SourceBase GateCollector Drain
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The top of the n-type channel is
connected through an ohmic contact
to a terminal referred to as the drain
(D), while the lower end of the samematerial is connected through an
ohmic contact to a terminal referred
to as the source (S).
The two p-type materials are
connected together and to the gate
(G)terminal.
In principle the drain and source areconnected to the ends of the n-type
channel and the gate to the two
layers ofp-type material.
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In the absence of any applied
potentials the JFET has two p-n
junctions under no-bias
conditions.
The result is a depletion region
at each junction as shown in Fig.
that resembles the same regionof a diode under no-bias
conditions.
A depletion region is that region
void of free carriers and
therefore unable to support
conduction through the region.
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A positive voltage VDS has been
applied across the channel.
Gate has been connected directlyto the source to establish the
condition VGS=0 volt.
The instant voltage VDS is
increased, the electrons will be
drawn to the drain terminal,
establishing the conventional
current ID with the defined
direction.
VGS= 0, VDS= + ve
BJT FET
Emitter SourceBase GateCollector Drain
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Water analogy for the JFET control
mechanism:
The source of water pressure can be
likened to the applied voltage from
drain to source that will establish a
flow of water (electrons) from the
tap (source).The gate, through an applied
signal (potential), controls the flow
of water (charge) to the drain.
The drain and source terminals areat opposite ends of the n-channel as
introduced in Fig. because the
terminology is defined for electron
flow.
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The path of charge flow clearly
reveals that the drain and
source currents are equivalent
(ID= IS).
The flow of charge is limited by
the resistance of the n-channel
between drain and source.
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The nonconductive depletion region becomes thicker with increased reverse bias.
(Note:The two gate regions of each FET are connected to each other.)
JFET is a voltage controlled device.
N-Channel JFET Operation
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7/18/2014 28
JFET Symbol :
JFET Ch t i ti
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JFET Characteristics
As the voltage VDSis increased from 0 to a few volts, the current will
increase as determined by Ohms law and the plot of IDversus VDS
will appear as shown below.
IDSSis the maximum drain currentfor a JFET
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The relative straightness of the plot reveals that for the
region of low values of VDS, the resistance is essentially
constant.
As VDSincreases the depletion region will widen, causing a
noticeable reduction in the channel width.
The reduced path of conduction causes the resistanceto
increase and the curve in the graph to occur.
The more horizontal the curve, the higher the resistance,
suggesting that the resistance is approaching infinite
ohms in the horizontal region.
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If VGS is increased to a level
where it appears that the
two depletion regions would
touch,a condition referred
to as pinch-offwill result.
At the pinch-offpoint:
Any further increase in VGSdoes not produce any increase in ID.
VGSat pinch-off is denoted as Vp.
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As VGSbecomes more negative:
the JFET will pinch-off at a lower voltage (Vp).
IDdecreases (ID< IDSS) even though VDSis increased.
Eventually IDwill reach 0A. VGSat this point is called Vpor VGS(off).
Also note that at high levels of VDS the JFET reaches a breakdown
situation. IDwill increase uncontrollably if VDS > VDSmax.
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FET as a Voltage-Controlled Resistor
The region to the left of the pinch-off point is called the ohmic region.
The JFET can be used as a variable resistor, where VGScontrols the
drain-source resistance (rd).
As VGSbecomes more negative, the resistance (rd) increases.
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Transfer (Transconductance) Curve
From this graph it is easy to determine the value of IDfor a given value of VGS.
It is also possible to determine IDSSand VPby looking at the knee where VGSis 0
Shockleys equation =
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p-Channel JFET:
p-Channel JFET operates in a similar manner as the n-channel JFET
except the voltage polarities and current directions are reversed
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P-Channel JFET Characteristics
As VGS
increases more positively,
the depletion zone increases
IDdecreases (ID< IDSS)
eventually ID= 0A
Also note that at high levels of VDS the JFET reaches a breakdown
situation. IDincreases uncontrollably if VDS> VDSmax.
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Problem 3 2 : Sketch the transfer curve for a n channel JFET
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Problem 3.2 : Sketch the transfer curve for a n-channel JFET
defined by IDSS= 12 mA and VP= -6 V.
Solution : Two plot points are defined by
At VGS =VP/2 = -6/2 =- 3 Vthe drain current will be determined by
ID= IDSS/4 = 12 /4 = 3 mA
At ID=I
DSS/2 = 12/2 = 6 mA the gate-to-
source voltage is determined by
VGS =0.3VP= 0.3 -6 = - 1.8 V
Using these four points the
complete transfer curve can be plotted.
=
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Problem 3.3: Sketch the transfer curve for ap-channel JFET
with IDSS = 4 mA and VP= 3 V.
Solution:
At VGS=VP/2 = 3/2 = 1.5 V,
ID=IDSS/4 = 4/4 = 1 mA.
At ID=IDSS/2 = 4 /2 = 2 mA,
VGS=0.3VP =0.33 = 0.9 V.
Using these points thecomplete transfer curve
can be plotted.
=
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MOSFET:
A MOSFET is Metal - Oxide - Semiconductor Field - Effect
Transistor.
There are two types of MOSFETs based on their basic
mode of operation, namely
a) Depletion type
b) Enhancement type
Depletion-type MOSFET (D-MOSFET) :
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Depletion type MOSFET (D MOSFET) :
There are three metal connections to the MOSFET : source,
drain, and gate. The source and drain are connected to n-
type semiconductor regions. These regions are connected by anarrow channelof n-type material [n-CHANNEL].
The source and drain regions and the n-channel are
embedded in a p-type substrate material.
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There is no direct electrical connection between the gate terminaland the channel of a MOSFET.
It is the insulating layer of SiO2 in the MOSFET construction that
accounts for the very desirable high input impedance of the device.
Hence itsa suitable device for amplification circuits.
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Drain and transfer characteristics for an n-channel
depletion-type MOSFET
If a varying voltage is applied to the gate of the
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If a varying voltage is applied to the gate of the
MOSFET, the source-drain current also varies.
A small variation in gate voltage VSG results in alarge variation in source-drain current, and a
correspondingly large output-voltage across the
resistor. Therefore, the MOSFET acts as a voltage
amplifier.
If a negative potential is applied to the gate, the n-
channel decreases in size when VSG increases. This
reduces the source-drain current and stops the
current when VSG is large. Thus MOSFET can be
used as on-off switch by changing the polarity of
VSG.
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D-MOSFET Symbol :
Problem 3 4 Sketch the transfer characteristics for an
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Problem 3.4: Sketch the transfer characteristics for an
n-channel depletion-type MOSFET with IDSS = 10 mA and
VP= - 4 V.
Solution :
At VGS
= +1 Volt,
=
Enhancement-type MOSFET (E-MOSFET) :
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Enhancement type MOSFET (E MOSFET) :
There is NO Channel !
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Both VDSand VGShave been set at some positive voltage
greater than 0 V, establishing the drain and gate at a
positive potential with respect to the source.
The positive potential at the gate will pressure the holes
(since like charges repel) in the p-substrate along the
edge of the SiO2layer to leave the area and enter deeper
regions of thep-substrate.
The result is a depletion region near the SiO2 insulating
layer void of holes.
As VGS increases in magnitude, the concentration ofelectrons near the SiO2surface increases until eventually
the induced n-type region can support a measurable flow
between drain and source.
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Summary Table
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Summary Table
JFET D-MOSFET E-MOSFET
Integrated Circuits:
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g
An integrated circuit (IC) is a collection of interconnected
transistors, diodes, resistors, and capacitors fabricated on a
single piece of silicon known as a chip.
ICs were invented partly to solve the interconnection
problem spawned by the transistor. In addition to solving
the interconnection problem, ICs possess the advantages ofminiaturization and fast response.
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Circuit layout of op-amp type 741
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Circuit layout of op amp type 741
The op-amp is a chip, a small black box with 8 connectors or pins (only 5 are usually used).
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Pin Configuration Symbol
Op-amp Equivalent
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Op-amp is equivalent to an electronic circuit consist of high
input resistor, a voltage source and a low output resistor.
p p q
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Powering the Op-Amp
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Powering the Op-Amp
Since op-amps are used as amplifiers, they need an
external source of (constant DC) power.Typically, this source will supply +15V at +V and -15V at -V.
The op-amp will give output voltage range of somewhat
less because of internal losses.
Op-Amp Intrinsic Gain
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Op Amp Intrinsic Gain
Amplifiers increase the magnitude of a signal by
multiplier called a gain A. The internal gain of an op-amp is very high. The exact
gain is often unpredictable.
This gain is called open-loop gainor intrinsic gain.
The output of the op-amp is this gain multiplied by the
input.
5 6outopen loop
in
VA 10 10
V
idout VAVVAV 21Gain A 2,00,000 for Op-amp IC 741Vid = V1-V2 is the input difference
Op Amp Saturation
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Op-Amp Saturation
The huge gain causes the output to change
dramatically when (V1-V2) changes sign.
However, the op-amp output is limited by the voltage
that you provide to it.
When the op-amp is at the maximum or minimumextreme, it is said to be saturated.
saturationnegativeVVthenVVif
saturationpositiveVVthenVVif
VVV
out
out
out
21
21
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The Non-Inverting Amplifier
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g
f
in
g
f
out
R
RAV
R
RV
11
The Non Inverting Amplifier
The Inverting Amplifier
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in
f
in
in
f
outR
RAV
R
RV
The Inverting Amplifier
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Subject Code : PHY 322
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