Module 3
OPERATIONAL AMPLIFIER
Brainstorming Session….
What does an AMPLIFIER do?
• What is an IC?
OP-Amp is an amplifier IC
What can you do with Op amps?
• You can make music louder when they are used in stereo
equipment.
• You can amplify the heartbeat by using them in medical
cardiographs.
• You can use them as comparators in heating systems.
• You can use them for Math operations like summing,
integration etc.
OP-AMP (operational amplifier)
• An OP-AMP is an integrated circuit (IC) used
for amplification of signals.
• It is the most widely used analog IC.
• It is used in control systems, instrumentation,
signal processing etc
Operational Amplifier
• The Operational Amplifier or "op-amp" is an
amplifier with two inputs and one output.
One input is the inverting input and the other
is a non inverting input.
OP-AMP BLOCK DIAGRAM
+V
Inverting Input
(- VIN)
Differential Voltage Output
Amplifier Amplifier Amplifier Output
Noninverting
Input (+ VIN)
-V
Figure 1 Op Amp Block Diagram
OP-AMP HAS 3 –STAGE AMPLIFIER
CIRCUITS
• First Stage : Differential Amplifier -it gives the
OP-AMP high input impedance (resistance)
• Second Stage: Voltage Amplifier – it gives high
gain
• Third Stage : Output Amplifier (Emitter
Follower) – gives low output impedance
(resistance)
OP-AMP CHARACTERISTICS
1. Very high input impedance
2. Very high gain
3. Very low output impedance
OP-AMP is a differential, voltage amplifier with
high gain.
OP-AMP is a differential, voltage amplifier
with high gain. Why????
• Differential Amplifier: Because it amplifies the
difference between 2 voltages
• Voltage Amplifier: Because input and output
are voltages
• High Gain Amplifier: Because the voltage gain
is very high (> 100,000)
The 741 Op-amp
The most common op-amp is the 741 IC.
Packaging Types
(b) OPA547FKTWT (c)
TO-5 metal can
8-Leads package
(a) Op Amp 741 DIP SMT package
8-pins DIP package
Figure : Op Amp packages
OP-AMP pins identification
741
1 8 1 8
+VCC +VCC
2 - 7 2 - 7
3 + 6 3 + 6
-VEE -VEE
4 5 4 5
a) Dot marked Package b) Notched Package
Figure 3 Op Amp pins Identification
What are these pins?
1. Offset
1 8
Null 8. N / C
741
2. Inverting Input –VIN
2 7 7. +VCC
3. Noninverting Input 3 6 6.Output
+VIN
- VEE 4 5
5.Offset Null
Figure 4 Op Amp pins Description
http://www.quia.com/pp/200743.html
What are these pins?
• Pin 1 and Pin 5 : Offset null input, are used to remove the
Offset voltage.
• Pin 2: Inverting input (-VIN), signals at this pin will be inverted
at output Pin 6.
• Pin 3: Non-inverting input (+VIN), signals at pin 3 will be
processed without inversion.
• Pin 4: Negative power supply terminal (-VEE).
• Pin 6: Output (VOUT) of the Op-Amp
• Pin 7: Positive power supply terminal (+VCC)
• Pin 8: No connection (N\C), it is just there to make it a
standard 8-pin
Symbol of OP-AMP
+VS
-VIN -VIN
- -
VOUT VOUT
+VIN +VIN
+ +
-VS
(a) Without power connection (b) With power connection
Figure 5 Op Amp Schematic Symbols
Most Op Amps require dual power supply
with common ground
Positive Supply (+15V) to pin7
Negative Supply (-15V) to pin4
+VS
-VIN
-
7
VOUT
+VIN
+ 4
Common Ground
-VS
Figure 6 Dual Supply Voltages connection
Some Op Amps work on single supply also
+VS
-VIN -VIN
- -
7 VOUT 7 VOUT
+VIN +VIN
4
+
4 +
-VS
(a) Single Positive Voltage (b) Single Negative Voltage
Figure 7 Single Supply Voltages connection
OP-AMP CONFIGURATIONS
(a) No Feedback (b) Negative (c) Positive Feedback
(open loop Feedback
comparator circuit) Figure Types of Feedback
Feedback
• No feedback : Open loop (used in
comparators)
• Negative feedback : Feedback to the inverting
input (Used in amplifiers)
• Positive feedback : Feedback to the non
inverting input (Used in oscillators)
OP AMP as a Comparator (compares 2
voltages and produces a signal to indicate
which is greater)
VO
+VS
+VS
+VIN > –VIN
–VIN
VO
0 +VIN = –VIN
+VIN
+VIN < –VIN
–VS
–VS
(a) Comparator Circuit (b) Comparator Output
Applications of Comparators
• Analog to digital converters (ADC)
• Counters (e.g. count pulses that exceed a
certain voltage level).
• Cross Over Detectors
OP-AMPS WITH NEGATIVE FEEDBACK
The two basic amplifier circuits with negative
feedback are:
• The non-inverting Amplifier.
• The inverting Amplifier
(Note: Negative feedback is used to limit the
gain)
NON-INVERTING AMPLIFIER
• The input signal is applied to the non-inverting input (+VIN).
The output is fed back to the inverting input through resistor
RF.
R + RF
VO = IN VF
R IN R1 RF
V R
A NI = O = 1 + F
VF R IN
Where; VIN VO
VO = Output voltage
Vin= Input voltage= Vf
ANI = Noninverting Gain
Figure 11 Closed-Loop Noninverting Amplifier Circuit
INVERTING AMPLIFIER
• The input signal is applied through a series input resistor RI to
the inverting input. Also, the output is fed back through RF to
the same input. The noninverting input is grounded.
R
VO = − F VIN
R IN RIN RF
V R
A I = O = - F
VF R IN VIN
Where; VO
VO = Output voltage
VIN = Input voltage
AI = Inverting Gain
Examples of Negative Feedback
Applications:
A) Inverting Amplifiers
1.Summing Amplifier
2.Differentiator
3.Integrator
B) Non Inverting Amplifiers
1. Voltage Follower
Summing Amplifier (Adder) : the inputs are added
and the sum is inverted . If all resistors are of equal
value, then
Vo = -(V1 + V2+ V3)
R1 RF
V1
R2
V2
VO
R3
V3
0V
Figure 14 Summing Amplifier
Integrator (the input is integrated with respect
to time)
VIN VO
Figure 15 Inverting Op-Amp as Integrator
Differentiator (the input is differentiated
with respect to time)
VIN VO
Figure 16 Inverting Op-Amp as Differentiator
Voltage Follower (Non Inverting)
• It is a non inverting amplifier with gain=1
• So the output is the same as input.
VO
VIN
Figure 17 Voltage Follower
Positive Feedback is used in oscillators
• Astable Multivibrator (Relaxation Oscillator)
C1 R1
VO
R2
R3
Figure 13 Astable Multivibrator
Offset Null Adjustment (practical)
• VO V
+VS
N/C
8 7 6 5
µA741
1 2 3 4
-VS
VIN = 0
Figure 22 Offset Null adjustment
• offset voltage can be defined as the slight
amount of voltage that appears at the output
when the voltage differential (ΔVIN) between
the input pins is 0 V.
Practical-Summing Amplifier
Results Table
Vo = - (V1 + V2 )
