AIR UNIVERSITY
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
EXPERIMENT NO 1
Lab Title: Characteristics of Bipolar Junction Transistor (BJT)
Student Name: UMAR AKHTAR Reg. No: 170879
Objective:
To determine transistor type (npn, pnp), terminals, and material using a digital multimeter
(DMM. To study the behavior of transistor as a switch. To examine the properties of a
MOSFET. To observe the effect of various biasing schemes.
LAB ASSESSMENT:
Excellent Good Average Satisfactory Unsatisfactory
Attributes (5) (4) (3) (2) (1)
Ability to Conduct
Experiment
Ability to assimilate the
results
Effective use of lab
equipment and follows
the lab safety rules
Total Marks: Obtained Marks:
LAB REPORT ASSESSMENT:
Excellent Good Average Satisfactory Unsatisfactory
Attributes
(5) (4) (3) (2) (1)
Data presentation
Experimental results
Conclusion
Total Marks: Obtained Marks:
Date: Mark Signature:
Characteristics of Bipolar Junction Transistor (BJT)
andMOSFET
UMAR AKHTAR (170879)
BACHELOR OF ELECTRICAL ENGINEERING
(Fall 17)
Submitted To:
Engr. Sharoze Sohail
Lab Engineer
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
FACULTY OF ENGINEERING
AIR UNIVERSITY,ISLAMABAD
Lab#01
Characteristics of Bipolar Junction Transistor (BJT) and
MOSFET
Objectives:
➢ To determine transistor type (npn, pnp), terminals, and material using a digital
multimeter (DMM).
➢ To study the behavior of transistor as a switch.
➢ To examine the properties of a MOSFET.
➢ To observe the effect of various biasing schemes.
Equipment:
➢ Transistor
➢ MOSFET
➢ Digital Multimeter
➢ Resistor
Discussion:
Bipolar Junction Transistor (BJT):
Bipolar transistors are made of either Silicon (Si) or Germanium (Ge). Their structure consists
of two layers of n-type material separated by a layer of p-type material (npn), or of two layers
of p-material separated by a layer of n-material (pnp). In either case, the center layer forms the
base of the transistor, while the external layers form the collector and the emitter of the
transistor. The three terminals of a transistor are following:
➢ Collector
➢ Base
➢ Emitter
NPN Transistor:
And its symbol is as
PNP Transistor:
And its symbol is as
MOSFET:
Previously, we have been considering BJTs, besides BJT, another more important three
terminal device is Metal-Oxide-Semiconductor Field-Effect-Transistor (MOSFET) or MOS.
MOSFETs are used more widely in industry for implementing digital designs. They are
preferredin industry because of their size (smaller), ease of manufacture and lesser power
utilization
Types of FET;
Modes of Operation and Voltage Transfer Characteristic Curve:
Biasing a MOSFET;
➢ Biasing using Gate-to-Drain Feedback Resistor
➢ Biasing using Fixed VG with Source Resistor
➢ NMOS as an Inverter
LAB TASKS;
Simulate all the given circuits in proteus and record all measurements required.
Transistor as a switch:
Protious circuit;
Reading table;
Sr no Vin IB IC Vc
1 0V 0 mA 0 mA 5V
2 5V 0.44mA 1.01mA 12mV
Biasing a MOSFET:
Biasing using Gate-to-Drain Feedback Resistor:
Reading table;
Sr no VD VGS VDS VG
1 2.18V 2.186 V 2.184 V 2.184
Biasing using Fixed VG with Source Resistor;
Reading table;
Sr no VD VGS VDS VG
1 8.26V 0V 0V 8.26
NMOS as an Inverter:
Reading table;
SR NO Vin Vout
1 0 5V
2 5 2.93V
B) Study about characteristic curves and regions of operation of both BJT and
MOSFET and include them in lab reports?
BJT CURVES
The forward biased junction in the BJT follows the same curve as we saw for the forward
biased diode. This set of characteristics obeys the same exponential relationship as the diode,
has the same turn on voltage (0.7V for Si and 0.2V for Ge at 25o C), and exhibits the same
temperature dependence (-2.0 mV/o C for Si and –2.5 mV/o C for Ge).
There are three distinct regions of these characteristics that are of importance:
➢ saturation region
➢ cutoff region
➢ active region
MOSFET CURVES;
MOSFETs are tri-terminal, unipolar, voltage-controlled, high input impedance devices which
form an integral part of vast variety of electronic circuits. These devices can be classified into
two types viz., depletion-type and enhancement-type, depending on whether they possess a
channel in their default state or no, respectively. In general, any MOSFET is seen to exhibit
three operating regions viz.,
➢ Cut-Off Region
➢ Ohmic or Linear Region
➢ Saturation Region
C) What is pinch off voltage in MOSFETS?
When the drain voltage is increased to a value known as the saturation voltage, VSAT, the
charge and current flow characteristics in an NMOS device evolve. The inversion layer under
the gate becomes wedge shaped, wider (or deeper) near the source and essentially disappears
(zero thickness) at the drain. This phenomenon is known as “pinch-off” and the point where
the inversion layer thickness is reduced to zero is called the “pinch-off point.” Pinch-off occurs
because, at VSAT, the effective potential between the gate and substrate at the source end of
the channel (Veff = VGS) is greater than the potential between the gate and the substrate at the
drain end of the channel, which is just the potential needed to form the inversion layer called
the threshold voltage (Veff = VGS-VSAT = VTH)
D) What is the difference between enhancement and depletion type MOSFETS? Attach
following proteus simulation files with lab reports?
In Enhancement MOSFET, the channel does not exist initially and is induced i.e the channel is
developed by applying a voltage greater than threshold voltage, at the gate terminals. On the
other hand, in depletion MOSFET, the channel is permanently fabricated (by doping) at the
time of construction of MOSFET itself.
E) Transistor as a switch MOSFET as a switch?
When using the MOSFET as a switch we can drive the MOSFET to turn “ON” faster or slower,
or pass high or low currents. This ability to turn the power MOSFET “ON” and “OFF” allows
the device to be used as a very efficient switch with switching speeds much faster than standard
bipolar junction transistors.
TRANSISTOR AS A SWITCH MOSFET AS A SWITCH
F) Transistor as an amplifier Transfer curve of MOSFET?
A transistor acts as an amplifier by raising the strength of a weak signal. The DC bias voltage
applied to the emitter base junction, makes it remain in forward biased condition. Thus a small
input voltage results in a large output voltage, which shows that the transistor works as an
amplifier
Transfer curves of mosfet
G) Biasing circuits of MOSFET with measurements.
DE-MOSFET Bias Circuits – DE-MOSFET bias circuits are similar to JFET bias circuits. Any
of the FET bias circuits already discussed can be used to produce a negative VGS level for an
n-channel MOSFET Biasing Circuits, or a positive VGS for a p-channel device. In this case,
both devices would be operating in the depletion mode, just like JFETs. To operate an n-
channel DEMOSFET in the enhancement mode, the gate terminal must be made positive with
respect to the source. A p-channel DE-MOSFET in the enhancement mode requires the gate to
be negative with respect to the source.
Conclusion;
From this lab we come to know about the basic working of transistors and mosfet also how
they operate in different regions of operation and also know about its different applications in
different things also comes to know about the depletion and enhancement region and pinch off
point and also we make the protious circuit of different circuit which are given we also perform
the same experiments in the lab and practically measure and see the working of these circuits
