Transcript Unit Three - geetaselectronics

Module 3
OPERATIONAL AMPLIFIER
Brainstorming Session….
What does an AMPLIFIER do?
• What is an IC?
Integrated Circuits
Inside 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
Amplifier
Voltage
Amplifier
Output
Amplifier
Noninverting
Input (+ VIN)
-V
Figure 1 Op Amp Block Diagram
Output
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
(a) Op Amp 741
DIP SMT package
8-pins DIP package
Figure : Op Amp packages
(c)
TO-5 metal can
8-Leads package
OP-AMP pins identification
1
2
3
4
+VCC
-
+
-VEE
8
1
7
2
6
3
5
4
a) Dot marked Package
741
+VCC
-
7
6
+
-VEE
b) Notched Package
Figure 3 Op Amp pins Identification
8
5
What are these pins?
1. Offset
Null
1
8
8. N / C
2
7
7. +VCC
3. Noninverting Input
+VIN
3
6
6.Output
VEE
4
5
2. Inverting Input –VIN
-
741
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
+VIN
+VIN
+
VOUT
7
+
4
4
-VS
(a) Single Positive Voltage
(b) Single Negative Voltage
Figure 7 Single Supply Voltages connection
Advantage of dual power supply
Using dual power supply will let the op amp to
output true AC voltage.
+15V
Output
0V
Output
30 V
-15V
Figure 8a Op Amp powered from Dual supply
+30V
30 V
0V
Figure 8b Op Amp powered from Single supply
What is dual power supply?
Single Power Supply
–15V
Single Power Supply
Common
Figure 18 Dual Power Supply
+15V
How can you make a dual power supply
using two 9V batteries?
What is the voltage between + of first battery
and – of second battery?
OP-AMP CONFIGURATIONS
(a) No Feedback
(open loop
comparator circuit)
(b) Negative
Feedback
Figure Types of Feedback
(c) Positive 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
(a) Comparator Circuit
–VS
(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 IN  R F 
 VF
VO  
 R IN 
V
R
A NI  O  1  F
VF
R IN
Where;
VO = Output voltage
Vin= Input voltage= Vf
ANI = Noninverting Gain
R1
RF
VIN
Figure 11 Closed-Loop Noninverting Amplifier Circuit
VO
Problem:
• Calculate the gain of a non inverting amplifier
if Rin=3K and Rf=30K. If Vin=4mV, calculate the
output voltage.
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 
AI 
R 
VO
 -  F 
VF
 R IN 
Where;
VO = Output voltage
VIN = Input voltage
AI = Inverting Gain
RIN
RF
VIN
VO
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)
C
R
VIN
VO
Figure 15 Inverting Op-Amp as Integrator
Differentiator (the input is differentiated
with respect to time)
R
C
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)
R1
C1
VO
R2
R3
Figure 13 Astable Multivibrator
Offset Null Adjustment (practical)
•
VO
V
+VS
N/C
8
7
6
5
3
4
A741
1
2
-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 )