NETAJI SUBHASH ENGINEERING COLLEGE
Department Of Electronics and Communication Engg.
Electronics Devices Laboratory (EC391)
ECE 2nd Year, 3rd Semester
EXPERIMENT NO. 6A
NAME OF THE EXPERIMENT: Study of Input Characteristic of Bipolar Junction Transistor for CE mode .
OBJECTIVE : To plot the input characteristics of Bipolar Junction Transistor and to find the following
parameters.
1. Dynamic input resistance
2. Common emitter current gain
EQUIPMENTS & COMPONENTS REQUIRED:
SL.NO. COMPONENTS QUANTITY
1. Resistors 2
2. Connecting Wires
3. Bread Board 1
4. BJT(BC547) 1
SL.NO. EQUIPMENTS QUANTITY
1. Regulated DC Power Supply 1
2. Digital Multimeter 2
3. Analog Multimeter 1
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 1
SYMBOL AND PIN DIAGRAM:
Schemtaic symbol of NPN & PNP BJT Physical view of BJT
CIRCUIT DIAGRAM
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 2
BRIEF THEORY:
In the Diode, we saw that simple diodes are made up from two pieces of semiconductor material, either
silicon or germanium to form a simple PN-junction and we also learnt about their properties and
characteristics. If we now join together two individual signal diodes back-to-back, this will give us two PN-
junctions connected together in series that share a common P or N terminal. The fusion of these two
diodes produces a three layer, two junction, three terminal device forming the basis of a Bipolar Junction
Transistor, or BJT for short.
Transistors are three terminal active devices made from different semiconductor materials that can act as
either an insulator or a conductor by the application of a small signal voltage. The transistor's ability to
change between these two states enables it to have two basic functions: "switching" (digital electronics)
or "amplification" (analogue electronics). Then bipolar transistors have the ability to operate within three
different regions:
1. Active Region - the transistor operates as an amplifier and Ic = β.Ib
2. Saturation - the transistor is "fully-ON" operating as a switch and Ic = I(saturation)
3. Cut-off - the transistor is "fully-OFF" operating as a switch and Ic = 0
The word Transistor is an acronym, and is a combination of the words Transfer Varistor used to describe
their mode of operation way back in their early days of development. There are two basic types of bipolar
transistor construction, PNP and NPN, which basically describes the physical arrangement of the P-type
and N-type semiconductor materials from which they are made. The Bipolar Transistor basic construction
consists of two PN-junctions producing three connecting terminals with each terminal being given a name
to identify it from the other two. These three terminals are known and labelled as the Emitter ( E ), the
Base ( B ) and the Collector ( C ) respectively. Bipolar Transistors are current regulating devices that control
the amount of current flowing through them in proportion to the amount of biasing voltage applied to
their base terminal acting like a current-controlled switch. The principle of operation of the two transistor
types PNP and NPN, is exactly the same the only difference being in their biasing and the polarity of the
power supply for each type.
Bipolar Transistor Construction
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 3
The construction and circuit symbols for both the PNP and NPN bipolar transistor are given above with
the arrow in the circuit symbol always showing the direction of "conventional current flow" between the
base terminal and its emitter terminal. The direction of the arrow always points from the positive P-type
region to the negative N-type region for both transistor types, exactly the same as for the standard diode
symbol.
Bipolar Transistor Configurations
As the Bipolar Transistor is a three terminal device, there are basically three possible ways to connect it
within an electronic circuit with one terminal being common to both the input and output. Each method
of connection responding differently to its input signal within a circuit as the static characteristics of the
transistor vary with each circuit arrangement.
● 1. Common Base Configuration - has Voltage Gain but no Current Gain.
● 2. Common Emitter Configuration - has both Current and Voltage Gain.
● 3. Common Collector Configuration - has Current Gain but no Voltage Gain.
The Common Emitter (CE) Configuration
In the Common Emitter or grounded emitter configuration, the input signal is applied between the base,
while the output is taken from between the collector and the emitter as shown. This type of configuration
is the most commonly used circuit for transistor based amplifiers and which represents the "normal"
method of bipolar transistor connection. The common emitter amplifier configuration produces the
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 4
highest current and power gain of all the three bipolar transistor configurations. This is mainly because
the input impedance is LOW as it is connected to a forward-biased PN-junction, while the output
impedance is HIGH as it is taken from a reverse-biased PN-junction.
The Common Emitter Amplifier Circuit
In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing
into the transistor as the emitter current is given as Ie = Ic + Ib. Also, as the load resistance (RL) is
connected in series with the collector, the current gain of the common emitter transistor configuration is
quite large as it is the ratio of Ic/Ib and is given the Greek symbol of Beta, (β). As the emitter current for a
common emitter configuration is defined as Ie = Ic + Ib, the ratio of Ic/Ie is called Alpha, given the Greek
symbol of α. Note: that the value of Alpha will always be less than unity.
Since the electrical relationship between these three currents, Ib, Ic and Ie is determined by the physical
construction of the transistor itself, any small change in the base current (Ib), will result in a much larger
change in the collector current (Ic). Then, small changes in current flowing in the base will thus control the
current in the emitter-collector circuit. Typically, Beta has a value between 20 and 200 for most general
purpose transistors. By combining the expressions for both Alpha, α and Beta, β the mathematical
relationship between these parameters and therefore the current gain of the transistor can be given as:
Where: "Ic" is the current flowing into the collector terminal, "Ib" is the current flowing into the base
terminal and "Ie" is the current flowing out of the emitter terminal.
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 5
Then to summarise, this type of bipolar transistor configuration has a greater input impedance, current
and power gain than that of the common base configuration but its voltage gain is much lower. The
common emitter configuration is an inverting amplifier circuit resulting in the output signal being 180 o
out-of-phase with the input voltage signal.
PROCEDURE:-
For Input characteristics:
(i) Rig up the circuit as per the ckt diagram.
(ii) Set VCE =2v (say), vary VBE insteps of 0.1v and note down the corresponding I B. Repeat
the above procedures for 4v, 6v etc.
(iii) Plot the graph: VBE vs. IB for a constant VCE.
WORKSHEET
EXPERIMENT NO. 6A Date: / /
Name of the student: ……………………………………………………………………………………………….
Roll No: ……………………………
OBSERVATION TABLE
To measure base current with different base-emitter voltage keeping collector-emitter voltage constant
(Input Characteristics)
VCE = V CE =
VBE(Volts) IB(mA) VBE(Volts) IB(mA)
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 6
CALCULATIONS:-
Dynamic input resistance= slope of input characteristics= ………..
PERFORMANCE MARKS: -------------------------------------------------
(Signature of teacher)
NETAJI SUBHASH ENGINEERING COLLEGE
Department Of Electronics and Communication Engg.
Electronics Devices Laboratory (EC392)
ECE 2nd Year, 3rd Semester
EXPERIMENT NO. 6B
NAME OF THE EXPERIMENT: Study of Output Characteristic of Bipolar Junction Transistor for CE mode .
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 7
OBJECTIVE : To plot the output characteristics of Bipolar Junction Transistor and to find the following
parameters.
1. Dynamic output resistance
2. Common emitter current gain
EQUIPMENTS & COMPONENTS REQUIRED:
SL.NO. COMPONENTS QUANTITY
1. Resistors 2
2. Connecting Wires
3. Bread Board 1
4. BJT(BC547) 1
SL.NO. EQUIPMENTS QUANTITY
1. Regulated DC Power Supply 1
2. Digital Multimeter 2
3. Analog Multimeter 1
SYMBOL AND PIN DIAGRAM:
Schemtaic symbol of NPN & PNP BJT Physical view of BJT
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 8
CIRCUIT DIAGRAM
BRIEF THEORY:
In the Diode, we saw that simple diodes are made up from two pieces of semiconductor material, either
silicon or germanium to form a simple PN-junction and we also learnt about their properties and
characteristics. If we now join together two individual signal diodes back-to-back, this will give us two PN-
junctions connected together in series that share a common P or N terminal. The fusion of these two
diodes produces a three layer, two junction, three terminal device forming the basis of a Bipolar Junction
Transistor, or BJT for short.
Transistors are three terminal active devices made from different semiconductor materials that can act as
either an insulator or a conductor by the application of a small signal voltage. The transistor's ability to
change between these two states enables it to have two basic functions: "switching" (digital electronics)
or "amplification" (analogue electronics). Then bipolar transistors have the ability to operate within three
different regions:
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 9
1. Active Region - the transistor operates as an amplifier and Ic = β.Ib
2. Saturation - the transistor is "fully-ON" operating as a switch and Ic = I(saturation)
3. Cut-off - the transistor is "fully-OFF" operating as a switch and Ic = 0
The word Transistor is an acronym, and is a combination of the words Transfer Varistor used to describe
their mode of operation way back in their early days of development. There are two basic types of bipolar
transistor construction, PNP and NPN, which basically describes the physical arrangement of the P-type
and N-type semiconductor materials from which they are made. The Bipolar Transistor basic construction
consists of two PN-junctions producing three connecting terminals with each terminal being given a name
to identify it from the other two. These three terminals are known and labelled as the Emitter ( E ), the
Base ( B ) and the Collector ( C ) respectively. Bipolar Transistors are current regulating devices that control
the amount of current flowing through them in proportion to the amount of biasing voltage applied to
their base terminal acting like a current-controlled switch. The principle of operation of the two transistor
types PNP and NPN, is exactly the same the only difference being in their biasing and the polarity of the
power supply for each type.
Bipolar Transistor Construction
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 10
The construction and circuit symbols for both the PNP and NPN bipolar transistor are given above with
the arrow in the circuit symbol always showing the direction of "conventional current flow" between the
base terminal and its emitter terminal. The direction of the arrow always points from the positive P-type
region to the negative N-type region for both transistor types, exactly the same as for the standard diode
symbol.
Bipolar Transistor Configurations
As the Bipolar Transistor is a three terminal device, there are basically three possible ways to connect it
within an electronic circuit with one terminal being common to both the input and output. Each method
of connection responding differently to its input signal within a circuit as the static characteristics of the
transistor vary with each circuit arrangement.
● 1. Common Base Configuration - has Voltage Gain but no Current Gain.
● 2. Common Emitter Configuration - has both Current and Voltage Gain.
● 3. Common Collector Configuration - has Current Gain but no Voltage Gain.
The Common Emitter (CE) Configuration
In the Common Emitter or grounded emitter configuration, the input signal is applied between the base,
while the output is taken from between the collector and the emitter as shown. This type of configuration
is the most commonly used circuit for transistor based amplifiers and which represents the "normal"
method of bipolar transistor connection. The common emitter amplifier configuration produces the
highest current and power gain of all the three bipolar transistor configurations. This is mainly because
the input impedance is LOW as it is connected to a forward-biased PN-junction, while the output
impedance is HIGH as it is taken from a reverse-biased PN-junction.
The Common Emitter Amplifier Circuit
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 11
In this type of configuration, the current flowing out of the transistor must be equal to the currents flowing
into the transistor as the emitter current is given as Ie = Ic + Ib. Also, as the load resistance (RL) is
connected in series with the collector, the current gain of the common emitter transistor configuration is
quite large as it is the ratio of Ic/Ib and is given the Greek symbol of Beta, (β). As the emitter current for a
common emitter configuration is defined as Ie = Ic + Ib, the ratio of Ic/Ie is called Alpha, given the Greek
symbol of α. Note: that the value of Alpha will always be less than unity.
Since the electrical relationship between these three currents, Ib, Ic and Ie is determined by the physical
construction of the transistor itself, any small change in the base current (Ib), will result in a much larger
change in the collector current (Ic). Then, small changes in current flowing in the base will thus control the
current in the emitter-collector circuit. Typically, Beta has a value between 20 and 200 for most general
purpose transistors. By combining the expressions for both Alpha, α and Beta, β the mathematical
relationship between these parameters and therefore the current gain of the transistor can be given as:
Where: "Ic" is the current flowing into the collector terminal, "Ib" is the current flowing into the base
terminal and "Ie" is the current flowing out of the emitter terminal.
Then to summarise, this type of bipolar transistor configuration has a greater input impedance, current
and power gain than that of the common base configuration but its voltage gain is much lower. The
common emitter configuration is an inverting amplifier circuit resulting in the output signal being 180 o
out-of-phase with the input voltage signal.
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 12
Output Characteristics Curves of a Typical Bipolar Transistor
The most important factor to notice is the effect of Vce upon the collector current Ic when Vce is greater
than about 1.0 volts. We can see that Ic is largely unaffected by changes in Vce above this value and
instead it is almost entirely controlled by the base current, Ib. When this happens we can say then that
the output circuit represents that of a "Constant Current Source". It can also be seen from the common
emitter circuit above that the emitter current Ie is the sum of the collector current, Ic and the base current,
Ib, added together so we can also say that Ie = Ic + Ib for the common emitter (CE) configuration.
By using the output characteristics curves in our example above and also Ohm´s Law, the current flowing
through the load resistor, (RL), is equal to the collector current, Ic entering the transistor which inturn
corresponds to the supply voltage, (Vcc) minus the voltage drop between the collector and the emitter
terminals, (Vce) and is given as:
Also, a straight line representing the Dynamic Load Line of the transistor can be drawn directly onto the
graph of curves above from the point of "Saturation" ( A ) when Vce = 0 to the point of "Cut-off" ( B ) when
Ic = 0 thus giving us the "Operating" or Q-point of the transistor. These two points are joined together by
a straight line and any position along this straight line represents the "Active Region" of the transistor. The
actual position of the load line on the characteristics curves can be calculated as follows:
Then, the collector or output characteristics curves for Common Emitter NPN Transistors can be used to
predict the Collector current, Ic, when given Vce and the Base current, Ib. A Load Line can also be
constructed onto the curves to determine a suitable Operating or Q-point which can be set by adjustment
of the base current. The slope of this load line is equal to the reciprocal of the load resistance which is
given as: -1/RL
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 13
PROCEDURE:-
For Ouput characteristics:
(iv) Rig up the circuit as per the ckt diagram.
(v) Set IB=10μA (say),vary VCE insteps of 1v and note down the corresponding I C. Repeat
the above procedures for 40μA, 80μA etc.
(vi) Plot the graph: VCE vs. IC for a constant VCE.
WORKSHEET
EXPERIMENT NO. 6B Date: / /
Name of the student: ……………………………………………………………………………………………….
Roll No: ……………………………
OBSERVATION TABLE
To measure collector current with different collector-emitter voltage keeping base-emitter voltage
Constant (Ouput Characteristics)
IB = IB =
VCE(Volts) IC(mA) VCE(Volts) IC(mA)
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 14
CALCULATIONS:-
Dynamic output resistance=slope of out put characteristics=……..
Common emitter current gain (β) = IC / IB =
PERFORMANCE MARKS: -------------------------------------------------
(Signature of teacher)
STUDY OF INPUT CHARATERISTICS OF BJT IN CE CONFIGURATIONPage 15
