This document discusses transistors and operational amplifiers. It begins by providing an overview of the bipolar junction transistor (BJT), including its structure as a three-terminal device and how it can amplify small input signals at the collector. The document then covers transistor characteristics such as input and output characteristics, configurations including common emitter, common base, and common collector, and current relations. It also discusses MOSFETs and operational amplifiers at a high level.

1. Transistors
&
Opamp
15 October 2023 1

2. Contents
• Transistor (BJT) Structure
• Transistor characteristics and parameters
• DC operating point
• Transistor as an amplifier
• Transistor as a switch
• MOSFET
• Operational Amplifier
15 October 2023 2

3. Introduction
• The semiconductor device like a diode cannot amplify a
signal, therefore its application area is limited.
• The next development of semiconductor device after diode is a
BJT (bipolar junction transistor).
• It is a three terminal device. The terminals are – collector,
emitter, and base. Out of which the base is a control terminal.
• A signal of small amplitude applied to the base is available in
the “magnified” form at the collector of the transistor.
• Thus the large power signal is obtained from a small power
signal.
15 October 2023 3

4. http://www.bellsystemmemorial.com/belllabs_transistor.html
History of Transistors
1948 – The year of establishment of E&TC - COEP
15 October 2023 4

5. Why is it called transistor ?
• The term transistor was derived from the words
TRANSFER & RESISTOR.
• Transfers input signal current from a low resistance
path to a high resistance path.
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6. N-P-N transistor
N
N
P
C
E
B
Collector Base
Junction JC
Emitter Base
Junction JE
E
Emitter
B
Base
C
Collector
15 October 2023 6

7. The BJT – Bipolar Junction Transistor
Normally Emitter layer is heavily doped, Base layer is lightly doped and Collector
layer has Moderate doping.
npn pnp
n p n
E
B
C p n p
E
B
C
Cross Section Cross Section
B
C
E
Schematic
Symbol
B
C
E
Schematic
Symbol
15 October 2023 7

8. transistor currents
N
P
E
B
Collector Base
Junction JC
Emitter Base
Junction JE
E
Emitter
B
Base
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9. Number of P-N junctions and equivalent circuit
N
P
E
B
P
N
B
C
E
Emitter
C
Collector
B
Base
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10. An unbiased Transistor – Depletion region
• For an unbiased transistor no external power supplies are
connected to it
P
Junction
JEB
Emitter collector
N
Base
Junction
JCB
N
Depletion
region
Depletion
region
-
-
-
-
-
+
+
+
+
+
-
-
-
-
-
+
+
+
+
+
-
-
-
-
-
-
-
-
-
-
15 October 2023 10

11. Transistor biasing in the active region
Sr.
No.
Region of
operation
Base emitter
junction
Collector base
junction
application
1 Cutoff region Reverse
biased
Reverse
biased
transistor is OFF
2 Saturation
region
Forward
biased
Forward
biased
transistor is ON
3 Active
region
Forward
biased
Reverse
biased
Amplifier
15 October 2023 11

12. Transistor operation in the active region P-N-P
P
Junction
JEB
Emitter collector
N
Base
Junction
JCB
VEE
RE
+
-
RC
VCC
-
holes emitted
holes collected
Conventional
current
conventional
current
+
P P
N
IE = IC + IB
15 October 2023 12

13. Transistor operation in the active region N-P-N
common base configuration
P
Junction
JEB
Emitter collector
N
Base
Junction
JCB
N
VEE
RE
+
-
RC
VCC
+
-
Electron emitted
Electron collected
Emitter electron
current
Direction
Conventional
Current IC (INJ)
Direction
Conventional
Current IB
Direction
Conventional
Current IE
(injected collector current)
15 October 2023 13

14. Transistor configuration
• Depending on which terminal is made common to input and
output port there are three possible configurations of the
transistor. They are as follows:
• Common base configuration
• Common emitter configuration
• Common collector configuration
15 October 2023 14

15. 15 October 2023 15
 Definition: The configuration
in which the emitter of
the transistor is common
between base and collector
circuit is called a common
emitter configuration.
 base is the input terminal,
 collector is the output
terminal and
 emitter terminal is connected
as a common terminal for
both input and output.
 The input signal is applied
between the emitter and
base terminals
 output signal is taken across
the collector and emitter
terminals.

16. 15 October 2023 16
 Due to the forward bias voltage, the majority carriers in the base region experience a
repulsive force from the negative terminal of the battery
 similarly majority carriers in the emitter region experience a repulsive force from the
positive terminal of the battery.

17. 15 October 2023 17
a. Input characteristics
 The input characteristics
describe the relationship
between input current or base
current (IB) and input voltage or
base-emitter voltage (VBE).
 To determine the input
characteristics, the output
voltage VCE is kept constant at
zero volts and the input voltage
VBE is increased from zero volts
to different voltage levels.
 For each voltage level of input
voltage (VBE), the
corresponding input current (IB)
is recorded.
 The cut in voltage of a silicon
transistor is 0.7 volts and
germanium transistor is 0.3
volts.
 from the above graph, after 0.7 volts, a
small increase in input voltage (VBE)
will rapidly increases the input current
(IB).

18. 15 October 2023 18
a. Input characteristics
Dynamic input resistance (ri)
Dynamic input resistance is defined as the ratio of change in input voltage or base
voltage (VBE) to the corresponding change in input current or base current (IB), with
the output voltage or collector voltage (VCE) kept at constant.

19. 15 October 2023 19
b. Output characteristics
 The output characteristics
describe the relationship
between output current (IC) and
the output voltage (VCE).
 To determine the output
characteristics, the input current
or Base current IB is kept
constant at zero mA and the
output voltage VCE is increased
from zero volts to different
voltage levels.
 For each voltage level of the
output voltage VCB, the output
current (IC) is recorded.
Dynamic output resistance (ro): Dynamic output resistance is defined as the
ratio of change in output voltage or collector voltage (VCE) to the corresponding
change in output current or collector current (IC), with the input current or base
current (IB) kept at constant.

20. Current relations in CE configuration
• Current gain ( α)
• The current gain of a transistor in CE configuration is defined
as the ratio of output current or collector current (IC) to the
input current or Base current (IE).
• The current gain of a transistor in CE configuration is high.
Therefore, the transistor in CE configuration is used for
amplifying the current.
α= IC / IB
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21. 15 October 2023 21
 Definition: The configuration
in which the base of
the transistor is common
between emitter and
collector circuit is called
a common base
configuration. The common
base circuit arrangement for
NPN and PNP transistor is
shown in the figure
 emitter is the input terminal,
 collector is the output
terminal and
 base terminal is connected
as a common terminal for
both input and output.
 The input signal is applied
between the emitter and
base terminals
 output signal is taken across
the collector and base
terminals.

22. 15 October 2023 22
 Due to the forward bias voltage, the free electrons (majority carriers) in the emitter
region experience a repulsive force from the negative terminal of the battery
 similarly holes (majority carriers) in the base region experience a repulsive force
from the positive terminal of the battery.
 As a result, free electrons start flowing from emitter to base similarly holes start
flowing from base to emitter.
 Thus free electrons are flowing from emitter to base and holes are flowing from base
to emitter.

23. 15 October 2023 23
a. Input characteristics
 The input characteristics
describe the relationship
between input current (IE) and
the input voltage (VBE).
 To determine the input
characteristics, the output
voltage VCB (collector-base
voltage) is kept constant at zero
volts and the input voltage VBE
is increased from zero volts to
different voltage levels.
 For each voltage level of the
input voltage (VBE), the input
current (IE) is recorded on a
paper or in any other form.
 The cut in voltage of a silicon
transistor is 0.7 volts and
germanium transistor is 0.3
volts.
 from the above graph, after 0.7 volts, a
small increase in input voltage (VBE) will
rapidly increase the input current (IE).

24. 15 October 2023 24
a. Input characteristics
Dynamic input resistance (ri)
Dynamic input resistance is defined as the ratio of change in input voltage or emitter
voltage (VBE) to the corresponding change in input current or emitter current (IE),
with the output voltage or collector voltage (VCB) kept at constant.

25. 15 October 2023 25
b. Output characteristics
 The output characteristics
describe the relationship
between output current (IC) and
the output voltage (VCB).
 To determine the output
characteristics, the input current
or emitter current IE is kept
constant at zero mA and the
output voltage VCB is increased
from zero volts to different
voltage levels.
 For each voltage level of the
output voltage VCB, the output
current (IC) is recorded.
Dynamic output resistance (ro): Dynamic output resistance is defined as the
ratio of change in output voltage or collector voltage (VCB) to the corresponding
change in output current or collector current (IC), with the input current or emitter
current (IE) kept at constant.

26. Transistor operation in the active region N-P-N
common base configuration
P
JEB
Emitter collector
N
Base
JCB
N
Depletion
region
Depletion
region
-
-
-
-
-
+
+
+
+
+
-
-
-
-
-
+
+
+
+
+
-
-
-
-
-
-
-
-
-
-
RC
VCC
+
-
IC=ICBO
ICBO
Is a collector to base leakage current
With open emitter
ICBO is a reverse saturation
Current flowing due to the
Minority carriers between
Collector and base when the
Emitter is open. ICBO flows due to the reverse
Biased collector base junction.
ICBO is neglected as compared to IC

27. Current relations in CB configuration
• Current gain ( α)
• The current gain of a transistor in CB configuration is defined
as the ratio of output current or collector current (IC) to the
input current or emitter current (IE).
• The current gain of a transistor in CB configuration is less than
unity. The typical current gain of a common base amplifier is
0.98.
α= IC / IE
15 October 2023 27

28. 15 October 2023 28
 Definition: The configuration
in which the collector is
common between emitter
and base is known as CC
configuration.
 Base is the input terminal,
 Emitter is the output terminal
and
 Collector terminal is
connected as a common
terminal for both input and
output.
 The input signal is applied
between the Collector and
base terminals
 output signal is taken across
the collector and emitter
terminals.

29. 15 October 2023 29
a. Input characteristics
 The input characteristics
describe the relationship
between input current (IB) and
the input voltage (VBC).
 To determine the input
characteristics, the output
voltage VEC (is kept constant at
3 volts and the input voltage
VBC is increased from zero
volts to different voltage levels.
 For each voltage level of the
input voltage (VBC), the input
current (IB) is recorded on a
paper or in any other form.
Dynamic input resistance (ri)
Dynamic input resistance is defined as the ratio of change in input voltage or emitter
voltage (VBC) to the corresponding change in input current or base current (IB), with
the output voltage (VEC) kept at constant.

30. 15 October 2023 30
b. Output characteristics
 The output characteristics
describe the relationship
between output current (IE) and
the output voltage (VEC).
 To determine the output
characteristics, the input current
or base current IB is kept
constant at zero mA and the
output voltage VEC is increased
from zero volts to different
voltage levels.
 For each voltage level of the
output voltage VEC, the output
current (IE) is recorded.
Dynamic output resistance (ro): Dynamic output resistance is defined as the
ratio of change in output voltage (VEC) to the corresponding change in output
current (IE), with the input current (IB) kept at constant.

31. 15 October 2023 31
Current amplification factor (γ)
The current amplification factor is defined as the ratio of change in output current
or emitter current IE to the change in input current or base current IB. It is expressed
by γ.

32. Sr. No. Parameter CB CE CC
1 Common terminal
between input and
output
Base Emitter Collector
Conduction Angle 0 o 180 o 0 o
2 Input current IE IB IB
3 Output current IC IC IE
4 Current gain αDC = IC/IE
Less than one
βDC = IC/IB
High
γ = IE/IB
HIGH
5 Input Voltage Veb Vbe Vbc
6 Output voltage Vcb Vce Vec
7 Current gain Less than
unity
High High
15 October 2023 32

33. Sr. No. Parameter CB CE CC
8 Input resistance Very low (20Ω) Low (1KΩ) High(500kΩ)
9 Output resistance Very high (1M) High(40kΩ) Low (50Ω)
10 Application As
preamplifier
Audio
amplifier
Impedance
matching
11. Voltage gain Medium Large Less than 1
15 October 2023 33

34. Transistor Biasing
• What is meant by dc biasing of a transistor ?
• Depending on the application, a transistor is to be operated in
any of the three regions of operation namely cutoff, active and
saturation region.
• To operate the transistor in these regions the two junctions of a
transistor should be forward or reverse bias
15 October 2023 34

35. RC
RE CE
R2
R1
+VCC
C1
C2
VO
Vi
Signal to be
Amplified RL
Amplified signal
output Signal
R1 & R2 are Biasing
Resistor
C1 & C2 are
Coupling
Capacitors
Bypass Capacitor
Single Stage RC Coupled CE Amplifier
15 October 2023 35

36. BJT Switch
• When operated in
saturation, the BJT
acts as a closed
switch.
• When operated in
cutoff, the BJT acts as
an open switch.
15 October 2023 36

37. MOSFET
15 October 2023 37

38. FIELD-EFFECT TRANSISTORS ( FET)
• FETs are the uni polar devices because, unlike BJTs
that use both electron and hole current, they operate
only with one type of charge carrier.
• The two main types of FET’s are -
 Junction Field Fffect Transistor (JFET) and
 Metal Oxide Semiconductor Field Effect Transistor
(MOSFET)
15 October 2023 38

39. Current Controlled & Voltage Controlled Devices
15 October 2023 39

40. Field Effect Transistors - Classification
15 October 2023 40

41. MOSFET (IGFET)
• The MOSFET (metal oxide semiconductor field effect
transistor) is the category of FET.
• The MOSFET differs from the JFET in that it has no PN
junction structure; instead, the gate of the MOSFET is
insulated from the channel by a silicon dioxide (Sio2) layer.
• Two basic types of MOSFETS are :
 Depletion ( D ) MOSFET and
 Enhancement ( E ) MOSFET
• Because of the insulated gate, these devices are also called
as IGFET.
15 October 2023 41

42. ENHANCEMENT MOSFET ( E-MOSFET)
MOSFET was
invented by
Atalla & Dawon
at Bell Labs in
1959
15 October 2023 42

43. Linear & Saturation Regions
15 October 2023 43

44. Transfer & Drain Characteristics
15 October 2023 44

45. BJT MOSFET
It is a current controlled device. It is a voltage controlled device.
It is a bipolar device (Current flows due
to both majority & minority carriers).
It is a unipolar device (Current flows
due to only majority carriers).
Thermal Runaway can damage the BJT Thermal Runaway does not take place
Input resistance (Ri) is very low. Output resistance (Ro) is very high.
Transfer characteristics are linear in
nature.
Transfer characteristics are non-linear in
nature.
BJT is More sensitive than MOSFET MOSFET is less Sensitive
AC Voltage Gain is HIGH AC Voltage Gain is Less
Bigger in size. Smaller in size.
Regions of operation: Saturation – ON
Switch , Cut off – OFF Switch
Active – Amplifier
Regions of operation: Ohmic – ON
Switch ,Saturation – Amplifier ,
Cut off – OFF Switch
It is more noisy. It is less noisy.
Switching speed is less. Switching speed is high.
Symbol Symbol
15 October 2023 45

46. Operational
Amplifier
An operational amplifier (often op-amp or opamp) is
a DC coupled high-gain electronic voltage amplifier with
a differential input and usually, a single-ended output
15 October 2023 46

47. • Op-amp is basically a multistage amplifier which is uses
a number of amplifier stages interconnected to each
other in a complicated manner.
• The amplifier which could be configured to perform a
variety of operations such as amplification, addition,
subtraction, differentiation and integration.
• Hence the name is operational amplifier (OP-AMP)
• IC 741 is extremely popular and was used in a variety of
applications.
15 October 2023 47

48. Pin configuration of OP-AMP IC 741
15 October 2023 48

49. Symbol and terminal
741
2
3
4
7
6
-
+
+VCC positive supply voltage
-VEE negative supply voltage
Output
Inverting input
Non-Inverting input
15 October 2023 49

50. Op-amp symbols and packages.
Thomas L. Floyd
Electronic Devices, 6e and Electronic
Devices: Electron Flow Version, 4e
15 October 2023 50

51. Ideal differential amplifier
• An ideal differential amplifier is expected to amplify the
differential signal present between its two input signal.
• It is also the basic stage of an integrated Op-amp with
differential input.
3
5
Vd
Vo = V1 – V2
+
+
-
-
Ideal
Differential
Amplifier
15 October 2023 51

52. Differential Amplifier
• 2 inputs and 2 outputs
15 October 2023 52

53. Ideal
Differential
Amplifier (Ad=10)
3
5
Vd
Vo =Ad(V1 – V2)
+
+
-
-
Differential gain -
• Vo = Ad ( V1 – V2 )
Where Ad is called as the differential gain.
• The differential gain can be defined as the gain with which the
differential amplifier amplifies the differential signal.
Vo = Ad Vd as Vd = V1 – V2
Gain Ad = Vo / Vd decibel Vo=10 Vd 2V
Ad (dB) =10 log10 [ Vo / Vd ]
15 October 2023 53

54. Ideal
Differential
Amplifier
3
5
Vd
Vo = Ac(V1 – V2)
+
+
-
-
Common mode signal
• A common signal to both the input terminals ( i.e. V1=V2=V)
is called as common mode signal.
• Ac=V0/(Vc)=
• The output voltage produced by an ideal differential amplifier
is zero for the common mode signal.
15 October 2023 54

55. Block diagram of a typical OP-AMP
Input
Stage
Intermediate
stage
Level
shifting
stage
Output
Stage
Non-inverting
input
Inverting
input
+
-
Output
Dual input
Balanced
Output
Differential
amplifier
Dual input
unbalanced
Output
Differential
amplifier
Such as
Emitter follower
Using constant
Current source
Complementary
Symmetry
Push-pull
amplifier
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56. 15 October 2023 56

57. Ideal
Differential
Amplifier
V2
V1
Vd
Vo = A(V1 – V2)
+
+
-
-
Common mode rejection ratio (CMRR)
• CMRR is defined as the ratio of differential gain Ad and
common mode gain Ac. It is denoted by letter “ρ”
• CMRR = ρ = Ad / Ac
• =10log10(Ad/Ac) in decibel
• Ideally CMRR should be infinite and practically it should be as
high as possible.
15 October 2023 57

58. The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVVD
+
-
Ri
Vd= 0
Zero differential
Input voltage
Ri
8
Ro
0
AV
8
IB2= 0
IB1= 0
Vo = AVVD
15 October 2023 58

59. Important characteristics of OP-AMP IC 741
Sr. No. Characteristics Value for IC 741 Ideal value
1 Input resistance Ri 2 MΩ
2 Output resistance Ro 75 Ω 0
3 Voltage gain Av 2 X 105
4 Bandwidth BW 1 MHz
5 CMRR 90 dB
6 Slew rate S 0.5 V/μSec
7 Input offset voltage 2 mV 0
8 PSRR 150 μV/V 0
9 Input bias current
(Ib1+ib2)/2
50 nA 0
10 Input offset current
Ib1-Ib2
6 nA 0
8
8
8
8
8
15 October 2023 59

60. 15 October 2023 60

61. OP-AMP
-
+
VS
V1
RF
Vo
R1
+
-
V2
Vd
IB2 = 0
+ -
-
+
AV =
8
input
t
t
0
0
VS
VO
Expression for the closed loop voltage gain (AVF)
AVF = - RF / R1
vin = 2V Rf=10K R1=2k V0= A*Vin = -5*2 =-10
The negative sign indicates that there is a phase shift of 1800
Between the input and output voltages.
I
The Inverting Amplifier
15 October 2023 61

62. OP-AMP
-
+
VS
V1
RF
Vo
R1
+
-
V2
I2 = 0
+ -
-
+
AV =
8
input
t
t
0
0
VS
VO
I1 = 0
As input impedance of ideal Op-amp is infinite, the current
entering into both the input terminals of
Op-amp will have zero values. (I1 = I2 = 0 )
The Non-Inverting Amplifier
15 October 2023 62

63. The Voltage follower (unity gain buffer)
OP-AMP
-
+
VS
V1
RF = 0
Vo
+
-
V2
I2 = 0
+ -
-
+
AV =
8
I1 = 0
When R1 is infinite and RF = 0 the non-inverting amplifier
gets converted into a voltage follower or unity gain.
Av=1+Rf/R1
R1 =
8
15 October 2023 63

64. Conclusion
• Read the Instruction Manuals of equipment i.e. Car,
Washing m/c, Microwave oven, Cell phone, Laptop etc.
• BJT is used rarely.
• MOSFET is matured technology & used everywhere.
• MOSFET ckts have low dissipations, high swing &
integration.
• Device / Ckt / Chip / Application designers are well
respected. Less effect of recession.
• Classrooms may diminish; Hands on has only meaning.
• Knowledge of E&TC is must for every branch.
• Opamp is hot topic forever !
15 October 2023 64

65. Thank You
madanbmali@gmail.com
Mbmali.scoe@sinhgad.edu
hodetc.scoe@sinhgad.edu
Cell: 9822893167
15 October 2023 65