Module 3
-
Upload
amelia-davenport -
Category
Documents
-
view
31 -
download
0
description
Transcript of Module 3
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
Figure 1 Op Amp Block Diagram
Inverting Input (- VIN)
+V
-V
Output
Noninverting Input (+ VIN)
Differential Amplifier
Differential Amplifier
Voltage AmplifierVoltage
Amplifier
Output AmplifierOutput
Amplifier
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)
Packaging Types
Figure : Op Amp packages
)b (OPA547FKTWT
DIP SMT package)a (Op Amp 7418-pins DIP package
(c) TO-5 metal can8-Leads package
OP-AMP pins identification
Figure 3 Op Amp pins Identification
1
2
3
4 5
6
7
8+VCC
-VEE
-
+
741
b( Notched Package
1
2
3
4 5
6
7
8+VCC
-VEE
-
+
a( Dot marked Package
What are these pins?
Figure 4 Op Amp pins Description
1
2
3
4 5
6
7
81 .Offset Null
-VEE
8 .N / C
6.Output
741
7+ .VCC
3 .Noninverting Input +VIN
2 .Inverting Input –VIN
5.Offset Null
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
Figure 5 Op Amp Schematic Symbols
-VIN
+
-
+VIN
VOUT
-VIN
+
-
+VIN
VOUT
+VS
-VS
(a) Without power connection (b) With power connection
Most Op Amps require dual power supply with common ground
Positive Supply (+15V) to pin7Negative Supply (-15V) to pin4
Figure 6 Dual Supply Voltages connection
-VIN
+
-
+VIN
VOUT
+VS
-VS
7
4
Common Ground
Some Op Amps work on single supply also
Figure 7 Single Supply Voltages connection
-VIN
+
-
+VIN
VOUT
-VS
7
4
-VIN
+
-
+VIN
VOUT
+VS
7
4
(a) Single Positive Voltage (b) Single Negative Voltage
Advantage of dual power supply
Using dual power supply will let the op amp to output true AC voltage.
0V
+15V
-15V
Output
Figure 8a Op Amp powered from Dual supply
+30V
0V
Output
Figure 8b Op Amp powered from Single supply
30 V30 V
What is dual power supply?
Single Power Supply Single Power Supply
Figure 18 Dual Power Supply
Common +15V–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
Figure Types of Feedback
(a) No Feedback (open loop
comparator circuit)
(b) Negative 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(
+VS
VO
+VIN = –VIN
–VS
+VIN –VIN
+VIN –VIN
0VO
+VIN
+VS
–VS
–VIN
(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.
VOVIN
RFR1
Figure 11 Closed-Loop Noninverting Amplifier Circuit
Where;VO = Output voltage
Vin= Input voltage= VfANI = Noninverting Gain
IN
F
F
ONI
FIN
FINO
R
R 1
V
V A
V R
R R V
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
R-
V
V A
V R
R V
IN
F
F
OI
ININ
FO
Where;VO = Output voltage
VIN = Input voltageAI = Inverting Gain
VO
VIN
RFRIN
Examples of Negative Feedback Applications:
A) Inverting Amplifiers1.Summing Amplifier2.Differentiator3.Integrator B) Non Inverting Amplifiers1. Voltage Follower
Summing Amplifier (Adder) : the inputs are added and the sum is inverted . If all resistors are of equal
value, thenVo = -(V1 + V2+ V3)
Figure 14 Summing Amplifier
V1
VO
V2
V3
0V
R1
R2
R3
RF
Integrator (the input is integrated with respect to time)
Figure 15 Inverting Op-Amp as Integrator
R
C
VIN VO
Differentiator (the input is differentiated with respect to time)
Figure 16 Inverting Op-Amp as Differentiator
C
R
VIN VO
Voltage Follower (Non Inverting)
• It is a non inverting amplifier with gain=1• So the output is the same as input.
VIN
VO
Figure 17 Voltage Follower
Positive Feedback is used in oscillators
• Astable Multivibrator (Relaxation Oscillator)
VO
R2
R3
R1C1
Figure 13 Astable Multivibrator
Offset Null Adjustment (practical)
•
Figure 22 Offset Null adjustment
-VS
N/C
VO
+VS
VIN = 0
A741
1 2 3 4
5678
V
• 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.