AMERICAN INTERNATIONAL UNIVERSITY BANGLADESH
Faculty of Engineering
Laboratory Report Cover Sheet
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Laboratory Title: Determination of Characteristic Curve of a
Diode.
Experiment Number: 01 Due Date: 05/03/2025
Semester: Spring 2024-25
Subject Code: EEE 2104 Subject Name: ELECTRONIC DEVICES LAB
Section: D
Course Instructor: PROTIK PARVEZ SHEIKH Degree Program: CSE
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Group Number (if applicable): 01 Individual Submission
Group Submission √
NO Student Name Student Number Student Signature Date
.
Submitted by:
1 S.M. Ibrahim Walid Walid 05/03/2025
23-52347-2
Group Members:
2 Shafiullah Kawsar Siam 05/03/2025
23-55254-3
3 Amanur Rahman 23-52039-2 05/03/2025
Aman
For faculty use only:
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Faculty comments
Title: Study of JFET and MOSFET Characterization.
Introduction:
The most common transistor types are the Metal Oxide Semiconductor Field
Effect Transistors (MOSFETs) and the Bipolar Junction Transistors (BJT). BJTs-
based circuits dominated the electronics market in the 1960's and 1970's.
Nowadays most electronic circuits, particularly integrated circuits (ICs), are
made of MOSFETs. The BJTs are mainly used for specific applications like
analog circuits (e.g. amplifiers), high-speed circuits or power electronics.
There are two main differences between BJTs and FETs. The first is that FETs
are charge controlled devices while BJTs are current controlled devices. The
second difference is that the input impedance of the FETs is very high while
that of BJT is relatively low. As for the FET transistors, there are two main
types: the junction field effect transistor (JFET) and the metal oxide
semiconductor field effect transistor (MOSFET). The power dissipation of a
JFET is high in comparison to MOSFETs. Therefore, JFETs are less important if
it comes to the realization of ICs, where transistors are densely packed. The
power dissipation of a JFET based circuit would be simply too high. MOSFETs
became the most popular field effect device in the 1980's.
The combination of n-type and p-type MOSFETs allow for the realization of
the Complementary Metal Oxide Semiconductor (CMOS) technology, which is
nowadays the most important technology in electronics. All microprocessors
and memory products are based on CMOS technology. The very low power
dissipation of CMOS circuits allows for the integration of millions of
transistors on a single chip.
The objective of experiment is to become familiar with the characteristics of
JFETs and MOSFETs. The goals are:
1. To understand the basic operation of JFETs and MOSFETs and
determine the threshold voltage.
2. To measure the I-V characteristics and find the different
operating regions for both JFETs and MOSFETs.
Theory and Methodology:
JFETs Structure and Operation
Transistor is a kind of current-control device, and its generating current
includes electron flow and hole flow. The transistor is therefore referred to as
bipolar junction transistor. FET is a unipolar device, in which the current N-
channel FET is formed by electron flow and the current of p channel is
formed by hole flow. FET is a kind of voltage-control device. FET can also
perform the functions that general transistors (BJT) do, with the only
exception that the bias conditions and characteristics are different. Their
applications should thus be chosen in accordance with related advantages
and drawbacks.
The characteristics of FET are listed as follows:
➢ FET has very high input impedance, typically around 100 MΩ.
➢ When FET is used as switch, there is no offset voltage.
➢ FET is relatively independent of radiation, whereas BJT is very
sensitive to radiation (β value will be varied).
However, FET also has some drawbacks: compared with BJT, its product of
gain and bandwidth is smaller and it is easier to be damaged by static
electricity.
The internal structure of JFETs is shown in figure 1. The n-channel JFET is
formed by diffusing one pair of p-type region into a slab of n-type material.
On the contrary, the p-channel JFET is formed by diffusing one pair of n type
region into a slab of p-type material.
MOSFETs Structure and Operation
The MOSFETs are the most widely used FETs. Strictly speaking, MOSFET
devices belong to the group of Insulated Gate Field Effect Transistor (IGFETs).
As the name implies, the gate is insulated from the channel by an insulator.
In most cases, the insulator is formed by silicon dioxide (SiO2), which leads
to the term MOSFET. MOSETs like all other IGFETs have three terminals, which
are called Gate (G), Source (S), and Drain (D). In certain cases, the
transistors have a fourth terminal, which is called the bulk or the body
terminal. In PMOS, the body terminal is held at the most positive voltage in
the circuit and in NMOS, it is held at the most negative voltage in the circuit.
There are four types of MOSFETs: enhancement n-type MOSFET,
enhancement p-type MOSFET, depletion n-type MOSFET, and depletion p-
type MOSFET. The type depends on whether the channel between the drain
and source is an induced channel or the channel is physically implemented
and whether the current owing in the channel is an electron current or a hole
current. If the channel between the drain and the source is an induced
channel, the transistor is called enhancement transistor. If the channel
between the drain and source is physically implemented, then the transistor
is called depletion transistor. If the current owing in the channel is an
electron current, the transistor is called an n- type or NMOS transistor. If the
current flow is a hole current, then the transistor is called p-type or PMOS
transistor. Throughout the handout, we will concentrate on analyzing the
enhancement type MOSFET. The cross section of an enhancement NMOS
transistor is shown in figure 5. If we put the drain and source on ground
potential and apply a positive voltage to the gate, the free holes (positive
charges) are repelled
from the region of the substrate under the gate (channel region) due to the
positive voltage applied to the gate. The holes are pushed away downwards
into the substrate leaving behind a depletion region. At the same time, the
positive gate voltage attracts electrons into the channel region. When the
concentration of electrons near the surface of the substrate under the gate is
higher than the concentration of holes, an n region is created, connecting the
source and the drain regions.
The induced n-region thus forms the channel for current flow from drain to
source. The channel is only a few nanometers wide. Nevertheless, the entire
current transport occurs in this thin channel between drain and source. Now
if a voltage is applied between drain and source electrodes an electron
current can flow through the induced channel. Increasing the voltage applied
to the gate above a certain threshold voltage enhances the channel. In the
case of an enhancement type NMOS transistor the threshold voltage is
positive, whereas an enhancement type PMOS transistor has a negative
threshold voltage. So, for the current to flow from drain to source, the
condition that should be satisfied is VG > Vth, where VG is the gate voltage
and Vth is the minimum voltage required to form a channel between drain
and source so that carriers can ow through the channel. By changing the
applied gate voltage, we can modulate the conductance of the channel.
Depletion type MOSFETs use a different approach. The channel is already
conductive for gate voltages of 0V. Such kinds of MOS transistors are realized
by the physical implantation of an n-type region between the drain and the
source.
Apparatus:
➢ Multimeter
➢ J176 (p-channel JFET)
➢ 2N7000 (n-channel enhancement type MOSFET)
➢ Connecting wires
➢ Trainer board Procedure:
1. The circuit is connected as shown in Figure 9, with V S kept
constant at 10 V.
2. A 1 kΩ resistor is used as the load.
3. The gate voltage (VG) varies from 10 V to 20 V in steps of 1 V,
and the corresponding current through the resistor (I D) is measured.
4. Table 1 is completed.
5. The ID vs. VGS curve is plotted using the data from Table 1, and
the pinch-off voltage (VP) is determined.
Precautions:
Have your instructor check all your connections after you are done setting up
the circuit and make sure that you apply only enough voltage (within VDD) to
turn on the transistors and/or chip, otherwise it may get damaged.
MOSFET transistors are very susceptible to breakdown due to electrostatic
discharge. It is recommended that you always ground yourself before picking
up the MOSFET chip. Do not touch any of the pins of the chip.
Circuit Diagram:
Experimental Data:
characteristic curve of a JFET. Dain to-Source voltage, 𝑉𝐷𝑆 = 10 V.
Table 1: Measured data of the voltage and current for the transfer
Gate Voltage 𝑽𝑮𝑺 Drain Current 𝑰𝑫𝑺
(V) (mA)
0 0.99
0.5 0.95
1.5 0.76
1 0.92
2.5 0.79
2 0.55
3 0.01
3.5 0.01
characteristic curve of a JFET. Gate to-Source voltage, 𝑽𝑮𝑺 = 10 V.
Table 2: Measured data of the voltage and current for the transfer
Gate Voltage 𝑽𝑫𝑺 Drain Current 𝑰𝑫𝑺
(V) (mA)
0 0.00
3.5 0.28
4 0.60
4.5 1.05
5 1.41
5.5 1.91
6 2.28
characteristic curve of a MOSFET. Dain-to-Source voltage, 𝑽𝑫𝑺= 10 V.
Table 3: Measured data of the voltage and current for the transfer
Gate Voltage 𝑽𝑮𝑺 Drain Current 𝑰𝑫𝑺
(V) (mA)
0 0.00
3.5 0.22
4 1.02
4.5 1.02
5 1.02
characteristic curve of a JFET. Gate to-Source voltage, 𝑽𝑮𝑺 = 10 V.
Table 4 : Measured data of the voltage and current for the transfer
Gate Voltage 𝑽𝑫𝑺 Drain Current 𝑰𝑫𝑺
(V) (mA)
0 0.02
0.5 0.47
1 1.05
1.5 1.54
2 2.06
2.5 2.59
3 3.05
Conclusion:
• The experiment successfully demonstrated the transfer
characteristics and operating regions of JFETs and MOSFETs.
• Minor discrepancies highlight the importance of understanding
real-world factors, such as temperature and device tolerances, when
analyzing circuit behavior.
Reference(s):
[1] Robert L. Boylestad, Louis Nashelsky, Electronic Devices and Circuit
Theory, 9th Edition, 20072008
[2] Adel S. Sedra, Kenneth C. Smith, Microelectronic Circuits, Saunders
College Publishing, 3rd ed., ISBN: 0-03-051648-X, 1991.
[3] American International University–Bangladesh (AIUB) Electronic
Devices Lab Manual.
[4] David J. Comer, Donald T. Comer, Fundamentals of Electronic Circuit
Design, John Wiley & Sons Canada, Ltd., ISBN: 0471410160, 2002.
[5] J. Keown, ORCAD PSpice and Circuit Analysis, Prentice Hall Press (2001)
[6] Resistor values: https://www.eleccircuit.com/how-to-basic-use-resistor/,
accessed on 20 September 2023.
