edc sem 2 _1 unit topic
Post on 07-Aug-2018
235 Views
Preview:
TRANSCRIPT
-
8/20/2019 Edc Sem 2 _1 Unit Topic
1/26
2008 EDC Lesson 9- " , Raj Kamal, 1
EDC UNIT IV- Transistor and FET
Characteristics
LessonLesson--9:9: JFET and Construction ofJFET and Construction of
JFETJFET
-
8/20/2019 Edc Sem 2 _1 Unit Topic
2/26
2008 EDC Lesson 9- " , Raj Kamal, 2
1. Transistor 1. Transistor
-
8/20/2019 Edc Sem 2 _1 Unit Topic
3/26
2008 EDC Lesson 9- " , Raj Kamal, 3
Transistor DefinitionTransistor Definition
The transferred-resistance or transistor
is a multi-junction device that is capable
of • Current gain
• Voltage gain
• Signal-power gain
-
8/20/2019 Edc Sem 2 _1 Unit Topic
4/26
2008 EDC Lesson 9- " , Raj Kamal, 4
2. Field Effect Transistor (FET)2. Field Effect Transistor (FET)
-
8/20/2019 Edc Sem 2 _1 Unit Topic
5/26
2008 EDC Lesson 9- " , Raj Kamal, 5
Unipolar Field Effect Transistor (FET)Unipolar Field Effect Transistor (FET)
Based on invention in 1948 by Bardeen,
Brattain and Shockley
Contains one type of carriers electrons or holes
(unipolar)
-
8/20/2019 Edc Sem 2 _1 Unit Topic
6/26
2008 EDC Lesson 9- " , Raj Kamal, 6
The conventional bipolar transistor has twotype of current carriers of both polarities(majority and minority) and FET has onlyone type of current carriers, p or n (holes orelectrons)
The BJT is current controlled and FET isvoltage controlled current between twoother terminals
The Field Effect Transistor (FET) and BJTThe Field Effect Transistor (FET) and BJT
-
8/20/2019 Edc Sem 2 _1 Unit Topic
7/26
2008 EDC Lesson 9- " , Raj Kamal, 7
Fundamental difference betweenFundamental difference between tthe voltage and currenthe voltage and current
controlled Field Effect Transistor (FET) and BJT amplifiers,controlled Field Effect Transistor (FET) and BJT amplifiers,
respectivelyrespectively
FET+
ID
S BJTControlcurrent
IC
Control
voltage
VGS
G
– E
+
IB
-
8/20/2019 Edc Sem 2 _1 Unit Topic
8/26
2008 EDC Lesson 9- " , Raj Kamal, 8
Fundamental difference between JFET andFundamental difference between JFET and
BJT devicesBJT devices
JFET junction is reverse-biased, the gate
current is practically zero, and a very
high impedance at input whereas the base
current of the BJT is always some value
greater than zero, for example, in As
-
8/20/2019 Edc Sem 2 _1 Unit Topic
9/26
2008 EDC Lesson 9- " , Raj Kamal, 9
FET Definition
• Field effect transistor is a unipolar-transistor, which
acts as a voltage-controlled current device and is a
device in which current at two electrodes is
controlled by the action of an electric field at anotherelectrode.
• Field effect transistor is a device in which the
current is controlled and transported by carriers ofone polarity (majority) only and an electric field near
the one terminal controls the current between other
two.
-
8/20/2019 Edc Sem 2 _1 Unit Topic
10/26
2008 EDC Lesson 9- " , Raj Kamal, 10
Types of FETsTypes of FETs
The family of FETs may be divided into :
Junction FET
Depletion Mode MOSFET Enhancement Mode MOSFET
-
8/20/2019 Edc Sem 2 _1 Unit Topic
11/26
2008 EDC Lesson 9- " , Raj Kamal, 11
3. Junction Field Effect Transistor (JFET)3. Junction Field Effect Transistor (JFET)
-
8/20/2019 Edc Sem 2 _1 Unit Topic
12/26
2008 EDC Lesson 9- " , Raj Kamal, 12
JFET Definition
•JFET is a unipolar-transistor, which acts as avoltage controlled current device and is a device
in which current at two electrodes is controlled by
the action of an electric field at a p-n junction.
• Field effect transistor is a device in which the
current is controlled and transported by carriers of
one polarity (majority) only and an electric fieldat the p-n junction region controls the
current between other two.
-
8/20/2019 Edc Sem 2 _1 Unit Topic
13/26
2008 EDC Lesson 9- " , Raj Kamal, 13
Basic structure of JFETsBasic structure of JFETs
In addition to the channel, a JFET
contains two ohmic contacts: the source
and the drain. The JFET will conduct current equally
well in either direction and the source
and drain leads are usuallyinterchangeable.
-
8/20/2019 Edc Sem 2 _1 Unit Topic
14/26
2008 EDC Lesson 9- " , Raj Kamal, 14
nn--Junction FET and pJunction FET and p--JFET SymbolsJFET Symbols
G
+
D
+
S
–VGS
VDS
G
D
D
+VGS
VDS
S
-
8/20/2019 Edc Sem 2 _1 Unit Topic
15/26
2008 EDC Lesson 9- " , Raj Kamal, 15
Junction FET (JFET)Junction FET (JFET)
JFET consists of a piece of high-resistivitysemiconductor material (usually Si) whichconstitutes a channel for the majority carrierflow and a gate.
Conducting semiconductor channel between twoohmic contacts – source & drain The magnitudeof this current is controlled by a voltage appliedto a gate, which is a reverse-biased.
(Ohmic contacts means following Ohm’s law [I Vcurrent proportional to V under constant physicalcondition.)
-
8/20/2019 Edc Sem 2 _1 Unit Topic
16/26
2008 EDC Lesson 9- " , Raj Kamal, 16
N channel JFET structureN channel JFET structure
-
8/20/2019 Edc Sem 2 _1 Unit Topic
17/26
2008 EDC Lesson 9- " , Raj Kamal, 17
N N--channel JFET constructionchannel JFET construction
This transistor is made by forming a channelof N-type material in a P-type substrate.
Three wires are then connected to the device.
One at each end of the channel.
One connected to the substrate.
In a sense, the device is a bit like a PN- junction diode, except that there are two wires
connected to the N-type side.
-
8/20/2019 Edc Sem 2 _1 Unit Topic
18/26
2008 EDC Lesson 9- " , Raj Kamal, 18
nJFET construction and Electric field nnJFET construction and Electric field n--JFETJFET
channelchannel
-
8/20/2019 Edc Sem 2 _1 Unit Topic
19/26
2008 EDC Lesson 9- " , Raj Kamal, 19
nn--Junction FETs and pJunction FETs and p--JFETsJFETs
JFET is a high-input resistance device, while theBJT is comparatively low.
If the channel is doped with a donor impurity, n-type material is formed and the channel current will
consist of electrons. If the channel is doped with an acceptor impurity,
p-type material will be formed and the channelcurrent will consist of holes.
-
8/20/2019 Edc Sem 2 _1 Unit Topic
20/26
2008 EDC Lesson 9- " , Raj Kamal, 20
JFET Electric Field creation along the channelJFET Electric Field creation along the channel
-
8/20/2019 Edc Sem 2 _1 Unit Topic
21/26
2008 EDC Lesson 9- " , Raj Kamal, 21
JFET Electric Field Variation along theJFET Electric Field Variation along the
channelchannel
-
8/20/2019 Edc Sem 2 _1 Unit Topic
22/26
2008 EDC Lesson 9- " , Raj Kamal, 22
nn-- JFET and pJFET and p--JFETJFET
N-channel JFET have greater conductivity than p-channel types, since electrons have higher mobilitythan do holes; thus n-channel JFETs are
approximately twice as efficient conductorscompared to their p-channel counterparts.
-
8/20/2019 Edc Sem 2 _1 Unit Topic
23/26
2008 EDC Lesson 9- " , Raj Kamal, 23
DS n-channel n
Gate
DrainSource
GBasic structure
p+
p+
n
Depletion
region
S Dn-channel
GCross section
n
Channel
thickness
p+
p+
(a)
nDepletion
regions
n-channel
Metal electrode
Insulation
(SiO2)
p
S DG
p+
(b)
DS
G
Circuit symbol
for n-channel FET
-
8/20/2019 Edc Sem 2 _1 Unit Topic
24/26
2008 EDC Lesson 9- " , Raj Kamal, 24
SummarySummary
-
8/20/2019 Edc Sem 2 _1 Unit Topic
25/26
2008 EDC Lesson 9- " , Raj Kamal, 25
We learnt
• Definitions of transistor, FET and
JFET
• Construction JFET
• n-channel and p-channel JFET
-
8/20/2019 Edc Sem 2 _1 Unit Topic
26/26
2008 EDC Lesson 9- " , Raj Kamal, 26
End of Lesson 9End of Lesson 9
top related