PPT_ BXE Unit 2 (1).pptx

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* 1
Transistors
&
Opamp
Unit-II

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

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.
* 3

History of Transistors
* 4

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.
* 5

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
* 6

transistor currents
B
Base
E
Emitter
* 7

* 8
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
static characteristics of the transistor vary with each circuit arrangement.
• Common Base Configuration – has Voltage Gain but no Current
Gain.
• Common Emitter Configuration – has both Current and Voltage
Gain.
• Common Collector Configuration – has Current Gain but no
Voltage Gain.

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
- +
- +
- +
- +
- +
-
-
-
-
-
-
-
-
-
-
+ -
+ -
+ -
+ -
+ -
* 9

Transistor biasing
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
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
* 10

Transistor operation in the active region P-N-P
P
Junction
JEB
Emitter collector
N
Base
Junction
JCB
RE
+
-
RC
-
holes emitted
holes collected
Conventional
conventional
current
+
P P
N
cur*rent 11
VE
O
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Cs

Transistor operation in the active region N-P-N
common base configuration
P
Junction
JEB
Emitter collector
N
Base
Junction
JCB
N
VE
O
Ether Subjects: https://www.studymedia.in/fe/n
V
ot
Ce
Cs
RE
+
- -
Electron emitted
Electron collected
Emitter electron
Direction
Conventional
Current IC
+ (INJ)
Conventional
Current IB
Direction
Conventional
Current IE
(injected collector current) RC
Direction
cur*rent 12

Transistor operation in the active region N-P-N
common base configuration
P
JEB JCB
Emitter collector
N
Base
N
Depletion
region
Depletion
region
- +
- +
- +
- +
- +
-
-
-
-
-
+
+
+
+
+
-
-
-
-
-
-
-
-
-
-
RC
VCC
+
-
IC=ICB
O
ICBO
Is a collector to base leakage current
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
* 13
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mitehdoiap.ienn/fee/nmoittetser

RC
RE CE
R
2
R
1
C1
C2 V
Vi
Signal to
be
Amplified
RL
Amplified
Osignal
output
Signal
R1 & R2 are Biasing
Resistor
Single Stage RC Coupled CE Amplifier
+VCC
C1 & C2 are
Coupling
Capacitors
* Other Subjects: https://www.studymeBdiya.pina/fes/nsotCesapacitor 14

Biasing of CE amplifier
• Biasing circuit types
• Fixed bias circuit(Single base resistor biasing
• Collector to base bias circuit.
• Voltage divider based biased circuit(R1 and R2)
• Significance of component used in RC-coupled CE
configuration
• C1 & C2- coupling capacitance –blocks DC
• CE- Bypass capacitor-Used to bypass Re during AC
input to provide high voltage gain and Open circuit
when DC input to provide high stability to Q-point
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Current gain of CE
* 16

Characteristics of a transistor in CE configuration
•It is a graph of input current (IB) versus
input voltage (VBE) at a constant output
voltage (VCE). N
N
P
C
B
JC
JE
+
-
-
+
RB
IC
IB
IE
E
VCE
constant
VBE
VBB
VCC
VBE
IB
(μA) VCE = 4V 10V
0 0.7 1 2
The value of dynamic input resistance “Ri” is
low for CE
ΔIB
ΔVBE Ri=ΔVBE/ΔIB
VCE Constant
Input characteristics
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• It is a graph of output current (Ic)
versus output voltage (VCE) at a
constant input current (IB)
E
C
N-P-N Transistor
-
+
RE
B
+
-
RB
IC
IE
VCC
VCE
VBE
VBB
VCE
IB = 0
4
3
2
1
IC
(mA)
1 2 3 4
OtCheurtoSfufbrjeecgtiso:nhttps://www.studymedia.in/fe/notes
IB = 2μA
IB = 4μA
IB = 3μA
IB = 4μA
Saturation
region
Active
region
βdc = IC /IB
Output characteristics
* 18

0 1 2 3 4
4
3
2
1
IB (μA)
Transfer characteristics
IC (mA)
VCE constant
Slope = ΔIC / ΔIB = βac
β ac = ΔIC /
ΔIB
Other Subjβectds:cht=tpsI:C//w/wIwB.study
media.VinC/fEe/cnoontesstant
* 19

* 20
DC Load line and operating point of CE configuration

Comparison of CB-CE-CC
* 21

BJT Switch
• When operated in
saturation, the BJT
acts as a closed
switch.
• When operated in
cutoff, the BJT acts as
an open switch.
* 22

14 January 2022 1
MOSFET

14 January 2022 2
FIELD-EFFECT TRANSISTORS ( FET)
•FETs are the uni polar devices because they operate
only with one type of charge carrier.
•The two main types of FET’s are -
□Junction Field Effect Transistor (JFET) and
□Metal Oxide Semiconductor Field Effect Transistor
(MOSFET)

Field Effect Transistors - Classification
14 January 2022
3

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.
14 January 2022 4

ENHANCEMENT MOSFET ( E-MOSFET)-N channel
MOSFET was invented by Atalla &
Dawon at Bell Labs in 1959
14 January 2022 5

Operation of N-channel E- MOSFET
14 January 2022 6

Working of N-channel E- MOSFET
•Operation of N-ch E-MOSFET can be explain in two modes
1. VGS=0and VDS/VDD=+VE
ID=0 hence act as open switch
1. VGS=+VE(greaterthan VGST) and VDS/VDD=+VE
ID=+VEvalue

Transfer & Drain Characteristics
14 January 2022 8
Cutoff region
Ohmic region
Saturation region

Enhancement P-MOSFET

Enhancement P-MOSFET characteristics

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. Input resistance is very high
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
14 January 2022 11

16 January 2022 1
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

16 January 2022 2
•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)
•The integrated Op-amp offers all the advantages of
monolithic integrated circuits such as small size, high
reliability, reduced cost, less power consumption.
•IC 741 is extremely popular and was used in a variety of
applications.

Pin configuration of OP-AMP IC 741
16 January 2022 3

Symbol and terminal
2
4
7
6
-
741
+
+VCC positive supply voltage
Output
Inverting input
3
Non-Inverting input
-VEE negative supply voltage
The Operational Amplifier (op amp) was invented in the 40's.
Bell Labs filed a patent in 1941 and many consider the first
practical op amp to be the vacuum tube K2-W invented in 1952
16 January 2022
by George PhilbrO
ic
th
k
e.
r Subjects: https://www.studymedia.in/fe/notes 4

Op-amp symbols and packages.
Thomas L. Floyd
16 January 20E
2l2
ectronic Devices, 6e and Electronic
Devices: Electron Flow Version, 4e
5

16 January 2022 6
Manufactures of OP-AMP IC 741
• The manufactures of Op-amp ICs are companies
like Fairchild, National semiconductor, Motorola,
Texas Instruments and signetics.
• The identifying initials for some other companies
are as follows:
: MC 741
: CA 741
1. National semiconductors : LM 741
2. Motorola
3. RCA
4. Texas instruments
5. Signetics
: SN 52741
: N 5741

Ideal differential amplifier
with
• 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
differential input.
V
2
V
1
Vd
Vo = V1 – V2
16 January 2022 7
+
+
-
-
Ideal
Differential
Amplifier

Ideal
Differential
Amplifier
V
2
V
1
Vd
Vo = V1 – V2
16 January 2022 8
+
+
-
-
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
Ad (dB) =10 log10 [ Vo / Vd ]

Ideal
Differential
Amplifier
V
2
V
1
Vd
Vo = V1 – V2
16 January 2022 9
+
+
-
-
Common mode signal
• A common signal to both the input terminals ( i.e. V1=V2=V) is
called as common mode signal.
• The output voltage produced by an ideal differential amplifier
is zero for the common mode signal.

Block diagram of a typical OP-AMP
Intermediate
stage
Level
shifting
stage
Output
Stage
Non-inverting
input
Inverting
input
+
Input
- Stage
16 January 2022 10
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

16 January 2022 11

Input and output signals 1800 phase shift when the input signal is
applied to the inverting (-) terminal
2
3
4
7
6
-
741
+
+VCC
-VEE
Vo
Inverting input
input
Inverted Output signal
16 January 2022 12

Input and output signals 00 phase shift when the input signal is
applied to the Non-inverting (+) terminal
2
4
7
6
-
741
+
+VCC
-VEE
Vo
3
Non-Inverting
input
input
Non-Inverted Output signal
16 January 2022 13

Ideal
Differential
Amplifier
V
2
V
1
Vd
Vo = V1 – V2
+
+
-
-
Common mode rejection ratio (CMRR)
• Common mode rejection ration (CMRR) is the ability of a
differential amplifier to reject the common mode signal
successfully.
• 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
• Ideally CMRR should be infinite and practically it should be as
high as possible.
16 January 2022 14

Equivalent circuit of an OP-AMP
-
+
+ VCC
-VEE
Output
Inverting input
Non-Inverting input
RL
Ro
AVV
d
+
-
Vo
Ri
-
+
Vd
16 January 2022 15

The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVV
d
+
-
Ri
Vd= 0
Zero differential
Input voltage
8
Ro
0
AV
8
Ri
IB2= 0
IB1= 0
Vo = A V
V D
the open loop gain of an ideal OP-AMP is denoted by Av. It is the
differential voltage gain and its value for an ideal OP-AMP is infinite.
Important characteristics of Op-Amp
1. Infinite voltage gain ( A )
V
8
V D
Other Subj
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16 January 2022 16

The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVV
d
+
-
Ri
Vd= 0
Zero differential
Input voltage
8
Ro
0
AV
8
Ri
IB2= 0
IB1= 0
Vo = A V
V D
there is no loading of the source.
2. Infinite input resistance (Ri 🡺 ∞)
the input resistance Ri of an ideal OP-amp is infinite. Due to this,
the current flowing in each input terminal will be zero. I
due to infinite input resistance, almost any source canB1
drive itB2
and
= 0 I = 0
16 January 2022 17

The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVV
d
+
-
Ri
Vd= 0
Zero differential
Input voltage
8
Ro
0
AV
8
Ri
IB2= 0
IB1= 0
Vo = A V
V D
3. Zero output resistance ( RO = 0 )
the output resistance Ro of an ideal OP-amp is zero. Due to this,
the ideal Op-amp can handle infinite number of other devices.
16 January 2022 18

The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVV
d
+
-
Ri
Vd= 0
Zero differential
Input voltage
8
Ro
0
AV
8
Ri
IB2= 0
Vo = A V
V D
IB1= 0
4. Zero offset voltage
in practical Op-amps a small output voltage is present even though
both the inputs V1 ad V2 are having a zero value.
This voltage is called as the offset voltage.
for ideal Op-amp the offset voltage is zero.
That means output voltage is zero when input voltage is zero.
16 January 2022 19

The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVVD
+
-
Ri
Vd= 0
Zero differential
Input voltage
8
Ro
0
AV
8
Ri
IB2= 0
Vo = A V
V D
IB1= 0
5. Infinite Bandwidth
Bandwidth of an amplifier is the range of frequencies over which all
the signal frequencies are amplified almost equally.
The bandwidth of an ideal Op-amp is infinite. So it can amplify any
frequency from zero to infinite hertz.
Thus the gain of an ideal amplifier is constant from zero to infinite hertz.
16 January 2022 20

The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVVD
+
-
Ri
Vd= 0
Zero differential
Input voltage
8
Ro
0
AV
8
Ri
IB2= 0
Vo = A V
V D
IB1= 0
6. Infinite CMRR
for an Op-amp, the common mode rejection ratio (CMRR) id defined
as the ratio of differential gain to common mode gain.
CMRR is infinite for the ideal Op-amp.
Thus the output voltage corresponding to the common mode noise is zero.
16 January 2022 21

The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVVD
+
-
Ri
Vd= 0
Zero differential
Input voltage
8
Ro
0
AV
8
Ri
IB2= 0
IB1= 0
Vo = A V
V D
7. Infinite slew rate
the slew rate of an ideal Op-amp is infinite so that the output voltage
changes occur simultaneously with the input voltage changes.
16 January 2022 22

The ideal OP-AMP
-
+
Output
V2
V1
Ro
AVVD
+
-
Ri
Vd= 0
Zero differential
Input voltage
8
Ro
0
AV
8
Ri
IB2= 0
IB1= 0
Vo = A V
V D
8. Zero power supply rejection ratio (PSRR).
PSSR is a parameter which specifies the degree of the dependence
of the Op-amp output on the changes in power supply output. For an
ideal Op-amp, PSRR = 0. that means the output voltage does not
Change due to fluctuation in supply voltage
16 January 2022 23

16 January 2022 24
Important characteristics of OP-AMP IC 741
Sr. No. Characteristics Value for IC 741 Ideal value
1 Input resistance Ri 2 MΩ
8
2 Output resistance Ro 75 Ω 0
3 Voltage gain Av 2 X 105
8
4 Bandwidth BW 1 MHz
8
5 CMRR 90 dB
8
6 Slew rate S 0.5 V/μS
8
7 Input offset voltage 2 mV 0
8 PSRR 150 μV/V 0
9 Input bias current 50 nA 0
10 Input offset current 6 nA 0

Open loop configuration of OP-AMP
Vd
Vo = Av Vd
+
-
-
p
-Op
a
+ m
V1 +
V2
0
b
a
+V(SAT)
-V(SAT)
• The meaning of open loop operation is that there is
absolutely no feedback present from the output to input.
Vo = Av Vd
Vd
16 January 2022 25

Open loop configuration of OP-AMP
16 January 2022 26

16 January 2022 27
Why Op-amp not used as an amplifier in the open
loop configuration ?
• Due to very large open loop gain, distortion is
introduced in the amplified output signal.
• The open loop gain does not remain constant, it
varies with change in temperature and power
supply.
• The bandwidth of an Op amp in open loop mode is
very very small – almost zero
• For this reason the Op-amp is not used in practice
as an amplifier.
• However the Op-amp in open loop configuration
is used in application such as comparator.

16 January 2022 28
Close loop configuration of OP-AMP
• In the closed loop configuration some kind of
“feedback” is introduced in the circuit.
• A part of output is returned back or fed back to the
input.
• Types of feedback
□Positive feedback or Regenerative feedback
□Negative feedback or Degenerative feedback.

Positive feedback or regenerative feedback
• If the feedback signal and the original input signal
are in phase with each other then it is called as the
positive feedback.
• Positive feedback is used in the application such as
“Oscillators” and Schmitt triggers or regenerative
comparators.
16 January 2022 29

Negative feedback or Degenerative feedback
• If the signal is fed back to the input and the original
input signal are 1800 out of phase, then it is called as
the negative feedback.
• In the application of Op-amp as an amplifier, the
negative feedback is used.
16 January 2022 30

Negative feedback or Degenerative feedback
• In the amplifier circuits using Op-amp, a feedback resistor RF is
connected between the output and inverting terminal as
shown in figure to introduced a negative feedback.
2 O
• As the voltages V and V are 1800 out of phase, a fraction of
0
output voltage fed back to the input via RF will be 180 out of
phase with the input.
2
3
6
-
OP-
AM
+P
V2
V1
input
Output
RF
Feedback resistor
16 January 2022 31
Vo

16 January 2022 32
Advantages of Negative feedback
• Negative feedback is used in the amplifier circuits as they
provide the following improvements in the operation of an
amplifier:
• It stabilizes the gain.
• Reduces the distortion.
• Increases the bandwidth.
• Changes the values of input and output resistances.
• Reduces the effects of variation in temperature and supply
voltage on the output of the Op-amp.

Virtual short
-
+
Output
V2
V1
Ri
Vd
Ri
8
I = 0
Vo = AVVD
+VCC
-VEE
The input impedance Ri of an Op-amp is ideally infinite.
Hence current “I” flowing from one input terminal to the other will
be zero. Thus the voltage drop across Ri will be zero and both the
input terminals will be at same potential, in other words they are
virtually shorteOdth
teorS
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16 January 2022 33

-
OP-
AM
+P
S
V1
RF
Vo
R1
V +
-
V2
Vd
IB2 = 0
+ -
-
+
V
A =
8
input
16 January 2022 34
t
t
0
VS
VO
0
Expression for the closed loop voltage gain (AVF)
AVF = - RF / R1
The negative sign indicates that there is a phase shift of 1800
Between the input and output voltages.
I
The Inverting Amplifier

-
OP-
AM
+P
VS
V1
RF
Vo
R1
+
-
V2
2
I = 0
-
- +
+
V
A =
8
input
t
t
0
VS
VO
0
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 )
16 January 2022 35
The Non-Inverting Amplifier

The Voltage follower (unity gain buffer)
-
OP-
AM
+P
VS
V1
F
Vo
+
-
V
+ R =
-
0
-
+
V
A =
8
2
I2 = 0
I1 = 0
When R1 is infinite and RF = 0 the non-inverting amplifier
gets converted into a voltage follower or unity gain.
16 January 2022 36
R1 =
8

16 January 2022 37
Conclusion
Car,
•Read the Instruction Manuals of equipment i.e.
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
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 !
well

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