Introduction to Field-Effect Transistors (FETs)
Summary
TLDRThis lecture introduces Field Effect Transistors (FETs), comparing them to Bipolar Junction Transistors (BJTs). FETs are three-terminal, voltage-controlled devices, unlike BJTs which are current-controlled. FETs can be either n-channel or p-channel, used for amplification and switching. The lecture outlines the history of FETs, from early patents to modern MOSFETs, and discusses their high input impedance, temperature stability, smaller size, and lower sensitivity compared to BJTs.
Takeaways
- 🔬 Field Effect Transistors (FETs) and Bipolar Junction Transistors (BJTs) are both three-terminal devices, but FETs are voltage-controlled while BJTs are current-controlled.
- 🌐 FETs can be used for both amplification and switching, similar to BJTs.
- 🔋 FETs are unipolar devices, meaning they rely solely on either electrons or holes, unlike BJTs which are bipolar.
- 📡 There are two types of FETs: Junction Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).
- 🧬 JFETs can be further divided into n-channel and p-channel types, just like NPN and PNP BJTs.
- 🏗️ MOSFETs are also divided into two types: depletion mode (D-MOSFET) and enhancement mode (E-MOSFET), each with n-channel and p-channel variants.
- 📚 The concept of FETs was patented by Julius Edgar Lilienfeld in 1926 and Oscar Heil in 1934, but the actual devices were developed later.
- 🔎 The first JFET was made in the late 1950s, and the MOSFET, an improvement over JFET, was invented by Dawon Kahng in 1959.
- 🔌 FETs have a high input impedance compared to BJTs, which is an advantage in certain applications.
- 🌡️ FETs are more temperature stable than BJTs, making them suitable for environments with varying temperatures.
- 🏞️ FETs are smaller in size compared to BJTs, which is beneficial for miniaturization in electronic devices.
- 📡 BJTs are more sensitive to the applied signal than FETs, which can be a consideration in signal processing applications.
Q & A
What is the main focus of the new chapter introduced in the lecture?
-The main focus of the new chapter is Field Effect Transistors (FETs).
How are Field Effect Transistors (FETs) similar to Bipolar Junction Transistors (BJTs) in terms of terminals?
-Both FETs and BJTs are three-terminal devices. In BJTs, the terminals are base, collector, and emitter, whereas in FETs, they are gate, drain, and source.
What is the main difference between BJTs and FETs in terms of control mechanism?
-BJTs are current-controlled devices, with the output current (IC) being a function of the input current (IB). In contrast, FETs are voltage-controlled devices, where the output current (ID) is a function of the voltage between the gate and source (V_GS).
Why are Field Effect Transistors referred to as 'unipolar' devices?
-FETs are called 'unipolar' because they depend solely on either electrons or holes for conduction, unlike BJTs which are 'bipolar' and involve both types of charge carriers.
What are the two types of Field Effect Transistors discussed in the lecture?
-The two types of Field Effect Transistors discussed are Junction Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).
Who is credited with the initial patent of the Field Effect Transistor concept?
-The initial patents for concepts similar to FETs were by Julius Edgar Lilienfeld in 1926 and by Oscar Heil in 1934.
How do FETs compare to BJTs in terms of input impedance?
-FETs have a higher input impedance compared to BJTs.
What is the significance of the term 'Field Effect' in the name of Field Effect Transistors?
-The term 'Field Effect' refers to the electric field developed by charges that controls the conduction path of the output circuit in FETs.
Are FETs more temperature stable than BJTs?
-Yes, FETs are more temperature stable than BJTs.
How do the size and area occupied by FETs compare to those of BJTs?
-FETs are smaller in size and occupy less area than Bipolar Junction Transistors.
Which type of transistor is more sensitive to the applied signal, BJTs or FETs?
-BJTs are more sensitive to the applied signal compared to FETs.
Outlines
📚 Introduction to Field Effect Transistors
This paragraph introduces the topic of Field Effect Transistors (FETs), comparing them with Bipolar Junction Transistors (BJTs). The lecturer explains that both FETs and BJTs are three-terminal devices, with the terminals being the gate, drain, and source for FETs, and the base, collector, and emitter for BJTs. The paragraph also discusses the applications of FETs, which are similar to those of BJTs, and highlights the main difference between the two: BJTs are current-controlled devices, while FETs are voltage-controlled.
🔬 Characteristics of Field Effect Transistors
The second paragraph delves into the characteristics of FETs, emphasizing that they are unipolar devices, meaning they rely either on electrons or holes, unlike BJTs which are bipolar. It also explains the concept of n-channel and p-channel FETs, analogous to npn and PNP transistors. The paragraph mentions that FETs can be used for both amplification and switching. The hierarchy of FETs is outlined, distinguishing between Junction Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), with further classification into n-channel and p-channel types. The history of FETs is briefly touched upon, mentioning the initial patents and the evolution leading to the invention of the MOSFET by D. Kong in 1959.
🔍 Further Insights into Field Effect Transistors
The final paragraph provides additional insights into FETs, explaining the term 'Field Effect' and how it pertains to the electric field that controls the conduction path in FETs. It also compares the input impedance of FETs to that of BJTs, stating that FETs have a higher input impedance. The paragraph discusses the temperature stability of FETs, noting that they are more stable than BJTs. It also mentions the smaller size of FETs compared to BJTs and concludes with a comparison of sensitivity between BJTs and FETs, stating that BJTs are more sensitive to applied signals. The lecture concludes with an invitation for questions and a预告of the next presentation, which will discuss the construction and characteristics of JFETs.
Mindmap
Keywords
💡Field Effect Transistors (FETs)
💡Bipolar Junction Transistors (BJTs)
💡Terminals
💡Current Control
💡Voltage Control
💡Unipolar
💡n-channel FET
💡p-channel FET
💡Junction Field Effect Transistor (JFET)
💡Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
💡Input Impedance
Highlights
Introduction to Field Effect Transistors (FETs) and their comparison with Bipolar Junction Transistors (BJTs).
FETs and BJTs are both three-terminal devices.
BJT is a current-controlled device, while FET is a voltage-controlled device.
BJT is a bipolar device, whereas FET is a unipolar device.
FETs can be either n-channel or p-channel, similar to NPN and PNP transistors.
FETs can be used for amplification and switching, just like BJTs.
Classification of FETs into Junction Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).
JFETs are further divided into n-channel and p-channel types.
MOSFETs are also divided into n-channel and p-channel types.
History of Field Effect transistors, starting with patents by Julius Edgar Lilienfeld in 1926 and Oscar Heil in 1934.
The first FET was made in the 1950s, and MOSFET was invented by Dawon Kahng in 1959.
Field Effect transistors derive their name from the electric field that controls the conduction path.
FETs have a high input impedance compared to BJTs.
FETs are more temperature stable than BJTs.
FETs are smaller in size compared to Bipolar Junction Transistors.
BJTs are more sensitive to the applied signal than FETs.
Next lecture will discuss the construction and characteristics of Junction Field Effect Transistors (JFETs).
Transcripts
from this lecture we will start a new
chapter that is Field Effect transistors
and in this lecture I will give a small
introduction about the Field Effect
transistors I will give a small
introduction about the Field Effect
transistors we will try to understand
what are fs and also compare them with
bjts we will compare f
with bipolar Junction transistors so
this is what we will do in this lecture
now we will move to the first point and
in this point we will talk about
terminals we already know BJT is a three
terminal device
BJT is a
three terminal device and like BJT f is
also a three terminal device Fe
is also a three terminal device in this
figure you can see the first box is
representing the BJT and the second box
is representing the F and in case of BJT
we have three terminals this terminal is
the base terminal this terminal is the
collector terminal and this terminal is
the Amer terminal the
current IB is the input current and the
current I is the output current in case
of BJT and in case of F this terminal
here is the gate terminal this terminal
is the drain terminal this terminal here
is the source terminal and the potential
difference between these two
terminals is equal to V GS v subscript
GS this is the potential difference
between the gate terminal and the source
terminal and the current in this branch
that is the output current is equal to I
subscript D so BJT and F both are three
terminal devices now we will talk about
applications to a larger extent the
application of f is same as application
of BJT the application of
Fe is nearly same as application of
application of
BJT so we are done with the first point
now we will move to the second point and
in this point we will talk about what
type of device is f BJT is current
control device you can see here the
output current is IC and I is equal to
Beta time IB where IB is the input
current so the output current is
dependent on the input current so we say
BJT is a current
controlled
device on the other hand the current ID
is dependent on the voltage
vgs so f e is a voltage
controlled device and this is the main
difference
main difference between BJT and F BJT is
a current control device and F is a
voltage control device IC is a function
of current IB current
IC is the function of input current IB
on the other hand in case of f current
ID is the function of voltage VG s and
you can see in both the cases the output
currents are the functions of input
parameters so we can say that the output
currents in both the cases are
controlled by parameters of input
circuit vgs is the input voltage in case
of F and IB is the input current in case
of BJT so we are done with the second
point which is very important point
because this is the main difference
between BJT and F let's discuss the
third point if you remember the first
presentation on BJT then I told you BJT
is a bipolar device BJT is a bipolar
device and this word bipolar is
reflected in the name BJT b stands for
bipolar on the other hand the Field
Effect
transistor is unipolar is uni
polar this means F depends solely on
either electrons or holes so f is a
unipolar device because it depends
either on electrons or on holes so this
is all for the third point now we will
move to the fourth point and in case of
f we have
n channel f and
P channel f p channel f like npn
transistor and PNP transistor when the f
is dependent on electrons only then we
call the f n channel f and when F
depends only on holes we call that f p
channel f f can be used for
amplification as well as switching the
fourth point is f
can be used for
amplification and also for switching
like BJT we can use f for amplification
and for switching let's move to the
fifth point and the fifth point is
related to the hierarchy we are going to
follow in this
chapter the Field Effect
transistors can be broadly classified
into two types the first one is jat the
Junction Field Effect transistor and the
second one is Mos
fat metal oxide semiconductor Field
Effect transistor in this chapter we
have to focus on these two Field Effect
transistors we can further classify J
fat into two types the first one is n
Channel J fat and the second one is p
Channel J fat MOS fat we can classify in
into two types the first one is
dfat D mosfet and the second one is e
mosfet and again we can classify D
mosfet into two types n
Channel P Channel oset we can classify
into two types n Channel and P channel
so this is all about the hierarchy we
are going to follow in this chapter now
let's talk about the history of Field
Effect transistors this is the sixth
point the history of Field Effect
transistors the Field Effect transistor
was first patented by Julius Edgar
Lilian field
Julius
Edgar
Lilian field in
1926 and by Oscar hail by Oscar
hail in
1934 and this patents were not for the
actual F but for the concepts and f-
like devices in 1947 William shlay and
his team tried to make AF but failed
while they were trying to diagnose the
reasons for failures they discovered the
first transistor or Point contact
transistor and after one decade the
first jet was made and Mos fat which is
better than J fat was invented by D Kong
D Kong in
1959 so this was the history of Field
Effect transistors now we will move to
the next point and in this point we will
try to understand meaning of Field
Effect meaning of
field
effect in the name Field Effect
transistor in case of Field Effect
transistors an electric field is
developed by the charges present an
electric field is developed by the
charges present and this electric field
controls the conduction path of the
output circuit this electric field
controls controls the
conduction
path of the out output circuit so there
is an effect due to electric field and
because of this reason we call the
device Field Effect transistor now let's
move to the next point and in this point
we will talk about input impedance Field
Effect
transistors Field Effect
transistors have high input impedance
high input impedance as compared to bjts
in the next point we will talk about
temperature stability FS
FS are more temperature stable FS
are
more
temperature stable as compared to bjts
in the next point we will talk about
area occupied or the size of fets Field
Effect
transistors are smaller are
smaller than bipolar Junction
transistors the last point the last
point is related to
sensitivity bjts
bjts are more sensitive to the applied
signal as compared to the fets so this
is all for this lecture if you have any
doubt you may ask in the comment section
in the next presentation we will discuss
the construction and characteristics of
G fets Junction Field Effect transistors
so see you in the next presentation
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