Ppt for engineering students application on field effect
1. SDE2205.41 to 42
Department Of Technical Education
Andhra Pradesh
Name :K.Radhika.
Designation :Lecturer.
Branch: :ECE
Institute : Govt Polytechnic Masabtank
Hyderabad.
Year/semester :II semester.
Subject :Electronic Components and devices-II
Subject code :SDE-2205
Topic :Field effect transistor.
Duration :100min
Sub topic :Classification of Field Effect Transistors
Merits and demerits of FET over BJT
Teaching aids :animation & photographs
2. SDE2205.41 to 42
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Objectives
After completion of this Lesson we will be able to
understand
Classification Field Effect Transistor
Different types of FETS
Merits and demerits of FET over BJT
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Recap
In the previous sessions we have learnt
Transistors
Use of Transistor as an Amplifier
Applications of Transistors
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Field Effect Transistor
Field effect Transistor is a semiconductor device
which depends for its operation on the control
of current by an electric Field
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• The high input impedance,low output impedance and
low noise level make FET for superior of the bipolar
transistor.
Features
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FET
JFET MOSFET
N-channel p-channel Depletion type Enhancement type
p-channel
N-channel
p-channel
N-channel
Classification of Field Effect Transistors
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JFET
Based on the construction JFETS are of Two types
1.N Channel FET
2.P Channel FET
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JFET Symbol
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N Channel FET P Channel FET
Fig 4 . JFET symbols
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Construction
Drain
Source
GATE
For a N Channel
FET an N type
silicon Bar is
used
Heavily doped P
type material is
deposited on either
side of the bar to
form GATE
The two ends of
the bar are known
as Source and
Drain
Fig 3. Construction of N Channel FET
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Construction of FET
Source : The source is the terminal
through which majority carriers enter
the Silicon Bar
Drain : Terminal through which Majoroty
carriers leave the bar
Gate: controls Drain current and is
always reverse biased
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N channel P channel
D
S
G
CIRCUIT SYMBOLS OF MOSFET
D
G
S
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Metal oxide semiconductor field effect
transistor (MOSFET)
• MOSFET is an important
semiconductor device and is
widely used in many circuit
application.
• The input impedance of a
MOSFET is much more than that
if a FET because of very small
leakage current.
• MOSFETs has much greater
commercial Importance
than JFET
N Channel
Drain
Substrate
Gate
Source
Oxide
layer
p
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•The MOSFET can be used
in any of the circuits covered
for the FET.
•Therefore all the equations
apply equally well to the
MOSFET and FET in
amplifier connections.
N Channel
Drain
Substrate
Gate
Source
Oxide
layer
p
Metal oxide semiconductor field effect
transistor (MOSFET)
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•MOSFETs uses a metal
gate electrode (instead of
p-n junction in JFET),
separated from the semi
conductor by an Insulating
thin layer sio2 to modulate
the resistance of the
conduction channel.
N Channel
Drain
Substrate
Gate
Source
Oxide
layer
p
Metal oxide semiconductor field effect
transistor (MOSFET)
16. SDE2205.41 to 42
• It is also called as
insulated gate FET (IGFET)
•MOSFETs operates both
in the depletion mode as well
as an the enhancement
mode
N Channel
Drain
Substrate
Gate
Source
Oxide
layer
p
Metal oxide semiconductor field effect
transistor (MOSFET)
17. SDE2205.41 to 42
• There is only a single p-region. This is called substrate.
• A thin layer of metal oxide is deposited over the left side of
the channel.
• A metallic gate is deposited over the oxide layer. As silicon
dioxide is an insulator, therefore a gate is insulated from
the channel. For this reason MOSFET is some times
called insulated gate FET.
Differences between MOSFET and FET
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FET and BJT
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BJT
1. Bipolar device
2.Current controlled device
3.Low input impedance
4.Low thermal stabilty
5.Lower switching speeds
6.More noisy
7.Diffuicult to fabricate on IC
FET
1. Uni polar device
2. Voltage controlled
Device
3. High input impedance
(in Mega ohms)
4. Better thermal stability
5. High switching speeds
6. Less Noisy
7. Easy to fabricate
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FET has several advantages over BJT
1. Current flow is due to majority carriers only
2. Immune to radiation
3. High input resistance
4. Less noisy than BJT
5. No offset voltages at zero drain current
6. High thermal stability
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ADVANTAGES OF FET OVER BJT
20. SDE2205.41 to 42
DISADVANTAGES OF FET OVER BJT
• FETs have a drawback of smaller gain
bandwidth product compared to BJT.
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Summary
In this session we have learnt
About Field Effect Transistors
Classification of Field Effect Transistors
Symbols and types
Compare FET and BJT
Applications
Advantages,disadvantages
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The field effect transistors has carriers as
) Electrons.
) Holes.
) Either of the above.
) None of this.
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QUIZ
23. SDE2205.41 to 42
7. A unipolar transistor is a
(A) PN diode.
(B) NPN transistor.
(C) PNP transistor.
(D) FET.
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QUIZ
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QUIZ
8.Which statement about MOSFETs is false
(a) Depletion mode only.
(b) Enhancement mode only
(c) Both of above
(d) None of the above
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9. IGFET is a
(a)Square law device
(b)Half power law device
(c)3/2 power law device
(d)Linear device
QUIZ
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Frequently asked questions
1. Compare BJT and FET?
2. Compare P channel and N channel FETS ?
3. Classify FETs?
4. What is meant by MOSFETs ?
5. List the types MOSFETs ?
6. What are the modifications in FET to make MOSFET?
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