Post on 06-Apr-2018
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introduction
Chapter 5:
Operational Amplifiers
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introduction
Introduction
The operational amplifier or op-amp is a circuit ofcomponents integrated into one chip.
A typical op-amp is powered by two dc voltagesand has an inverting(-) and a non-inverting input(+) and an output.
An op amp is an electronic device which provides
a voltage output based on the voltage input
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introduction
Basic op-amp
Op-amp has two inputs that connect to two terminalsand one output
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introduction
Operational Amplifiers
Five important pins
2 The inverting input
3 The non-inverting input
6 The output
4 The negative power supply V- (-Vcc)
7 The positive power supply V+ (+Vcc)
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introduction
Operational Amplifiers
The output of the op amp is given by the followingequation:
Vd = E1 E2and Vo = AVOL(Vd)
AVOL is called the open-loop voltage gain because itis the gain of the op amp without any external feedbackfrom output to input
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introduction
Operational Amplifiers
Positive Saturationwhere the outputvoltage exceeds thepositive power input
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introduction
Operational Amplifiers
Linear Regionwhere the outputvoltage is linearbased on A (gain)
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introduction
Operational Amplifiers
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introduction
What do they really look like?
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introduction
IC Circuit
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introduction
Operational Amplifiers
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introduction
Operational Amplifiers
An ideal op-amp has infinite gain and bandwidth,
we know this is impossible.However, op-amps do have:
very high gain
very high input impedance(Zin= )
very low output impedance (Zout = 0)
wide bandwidth.
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application
Application in op-amp
There are 2 types of application in op-amp
Linear application
Non-linear application
Linear application is where the op-amp operatein linear region:
Assumptions in linear application:
Input current, Ii = 0
Input voltage: V+=V-
Feedback at the inverting input
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application
Non-linear application is where the op-ampoperate in non-linear region
By comparing these two input voltages:positive input voltages, V+ and negative input
voltage, V- where:
VO = VCC if V+ > V-
VO = -VEE if V+ < V-
Input current, Ii = 0
Application in op-amp
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application
Applications of op-amp
Comparator
Inverter
Audio amplifier
Difference Amplifier Filter
Summing Amplifier
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application
Inverting Amplifier
Non-Inverting Amplifier
Summing Amplifier
Unity Follower Difference Amplifier
Integrators
Differentiators
Op-amp Circuit Application
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application:inverting amplifier
Application: Inverting amplifier
Provide a constant gain multiplier
Input signal is connected to the inverting input of the op-
amp. Therefore, the output signal is 180 degree out ofphase from the input signal
Rf is the feed-back resistor to control the voltage gain ofthe op-amp
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application:inverting amplifier
Summary of op-amp behavior
Vo = A(V+ - V)
Vo/A = V+ - V
Let A infinity
then,
V+ - V 0
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application:inverting amplifier
V+ = V
I+ = I = 0
Seems strange, but the input terminals to anop-amp act as a short and open at the same time
Summary of op-amp behavior
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application:inverting amplifier
To analyze an op-amp circuit for linearoperation
Write node equations at + and - terminals
(Ii=I+ = I-= 0)
Set V+ = V-
Solve for Vo
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application:inverting amplifier
Analysis of inverting amplifier
I1
If
Ii
V = 0Ii= 0
I1= If Ii
Vs
V
R1
=
V
Vo
Rf
V
= V = 0
Vo
Vs
=-R
f
R1
Vo=-
Rf
R1
Vs
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application:non-inverting amplifier
Application:Non-inverting amplifier
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Non-inverting configuration
Vi= V = V
use KCL :
I1= I
iI2
while Ii= 0
;
so :0 V
R1
=
V Vo
R2
insert V
= Vi ;
0 Vi
R1
=
Vi V
o
R2
Vo= V
i1
R2
R1
Vi
I1
I2
Ii
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application:summing amplifier
Application: Summing amplifier
Virtual-ground equivalent circuit.
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Summing Amplifier
V1
V2
V3
R1
R2
R3
Rf
This circuit is calle
a weighted summer
V = V
= 0
use KCL :
IR1 IR2 IR3= Ii IRf
while Ii= 0 ;
so:V
1 V
R1
V2 V
R2
V3 V
R3
=
V
Vo
Rf
insert V
= 0 ;
V1
R1
V2
R2
V3
R3
=
Vo
Rf
Vo= R
f
V1
R1
V2
R2
V3
R3
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application:unity-follower
Application: Unity Follower
VO=
V1
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application:difference amplifier
Application:Difference amplifier
VO
=
R4
R2
V1
V2
R1= R
2
R3= R
4
A li i
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application:instrumentation amplifier
Application:Instrumentation Amplifier
R2
Buffer
R2
R1
R1
RA
RB
RA
Difference amplifier
VO=
R2
R1
12R A
RB
V2
V1
R2
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application:integrator
Application:Integrator
Feedback component = capacitor : Integrator
I IC
I= Ii ICv i t
R
= 0 Cdv0 t
dtv o t =
1
RC vi t dt
Capaci tan ce impedance :
XC=1
jC=
1
sC
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application:differentiator
Application:Differentiation
IC= IR
Cdv i t
dt
=
V vo t
R
v o t = RCdv i t
dt
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exercise
Exercise 1
Find VO?
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exercise
Exercise 2
Find V2 and V3?
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exercise
Exercise 3
Find VO?
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exercise
Exercise 4
Find VO?
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non-linear application
Non-linear application is where the op-ampoperate in non-linear region
By comparing these two input voltages:positive input voltages, V+ and negative input
voltage, V- where:VO = VCC if V
+ > V-
VO = -VCC if V+ < V-
Input current, Ii = 0
Recall: Non-linear application in op-amp
Non linear application:
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non-linear application:comparator
Non-linear application:Comparator
Non-linear application:
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non-linear application:comparator
Non-linear application:Comparator
Vo(V)
10
-5
t
VS(V)
t
Compare V+ and V-
V+=0V-=VS
When:VS>0,V
+>V- so Vo=10VVS
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non-linear application:schmitt trigger
Non-linear applicationSchmitt Trigger
-
+
V =R 1
R1 R fVO
Positive Feedback
Non-linear application
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non-linear application:schmitt trigger
V =R1
R1
RfV
O
assume R1= R f and VCC= VEE= 15 V
with initial state Vo= 15 V and
VS=
V=
10 sin t V
V =1
215 = 7 . 5 V
Non linear applicationSchmitt Trigger
Vo(V)
15
-15
t
VS(V)
t
7.5
-7.5
Vo(V)
VS(V)-7.5 7.5-10 10
15
-15
(a) Transfer Characteristic of Schmitt Trigger
(c) Output Voltage of Schmitt Trigger
(b) Input Voltage of Schmitt Trigger