8/3/2019 Ipg Iiitm Op Amp
1/42
1
Basic Electrical Engineering
Operational Amplifier
8/3/2019 Ipg Iiitm Op Amp
2/42
Operational Amplifiers
An operational amplifier (op-amp) is a DC-coupledhigh-gain electronic voltage amplifier with a differential
inputs and a single-ended output.
An op-amp produces an output voltage that is typicallyhundreds of thousands times larger than the voltage
difference between its input terminals.
They had their origins in analog computers where they
were used in many linear, non-linear and frequency-
dependent electrical and electronics circuits.
8/3/2019 Ipg Iiitm Op Amp
3/42
Background
Originally invented in early 1940s using vacuum tubetechnology
Initial purpose was to execute math operations in
analog electronic calculating machines
Small in size with invention of transistor Now made on integrated circuit (IC)
Only most demanding applications use discrete
components
Huge variety of applications, in electrical andelectronics ckts, low cost, and ease of mass production
make them extremely popular
8/3/2019 Ipg Iiitm Op Amp
4/42
Op-amp Circuit notation
The circuit symbol for an op-amp :
V+: non-inverting input
V-: inverting input
Vout: output
Vs+ or Vcc+: positive power supply
Vs- or Vcc-: : negative power supply
http://en.wikipedia.org/wiki/File:Op-amp_symbol.svg8/3/2019 Ipg Iiitm Op Amp
5/42
Op-amp: Operation
The amplifier's differential inputs consist of a V+
input and
a V- input, and ideally the op-amp amplifies only the
difference in voltage between the two, which is called
the differential input voltage. The output voltage of the
op-amp is given by the equation
Vout = (V+ - V-) AOL
AOL is the open loop gain of the amplifier.
The magnitude ofAOL
is typically very large for Integrated
Circuit (IC) op-amps and therefore even a quite small
difference between and drives the amplifier output
nearly to the supply voltage. This is called saturation of
the amplifier.
http://en.wikipedia.org/wiki/File:Op-amp_open-loop_1.svg8/3/2019 Ipg Iiitm Op Amp
6/42
Input offset voltageVoltage required across the op-amp's input terminals to
drive the output voltage to zero, is related to themismatches in input bias current.
In the perfect amplifier, there would be no input offset
voltage. However, it exists in actual op-amps because
of imperfections in the differential amplifier:Input offset voltage creates two problems:
1. due to the amplifier's high voltage gain, it virtually
assures that the amplifier output will go into
saturation if it is operated without negative feedback.2. In a closed loop, negative feedback configuration, the
input offset voltage is amplified along with the signal.
8/3/2019 Ipg Iiitm Op Amp
7/42
Common-mode gain
A perfect operational amplifier amplifies only the voltage
difference between its two inputs, completely rejectingall voltages that are common to both.
However, the differential input stage of an operational
amplifier is never perfect, leading to the amplification
of these identical voltages to some degree. Thestandard measure of this defect is called the common-
mode rejection ratio (denoted CMRR). Minimization of
common mode gain is usually important in non-
inverting amplifiers that operate at high amplification.
http://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratio8/3/2019 Ipg Iiitm Op Amp
8/42
Positive feedback applications
which takes a fraction of the output signal back to thenon-inverting input.
Application: Comparator with hysteresis, the Schmitt
trigger.
Some circuits may use Positive feedback and Negativefeedback around the same amplifier, for example
Triangle wave oscillators and active filters.
http://en.wikipedia.org/wiki/Triangle_wavehttp://en.wikipedia.org/wiki/Oscillatorshttp://en.wikipedia.org/wiki/Active_filtershttp://en.wikipedia.org/wiki/Active_filtershttp://en.wikipedia.org/wiki/Active_filtershttp://en.wikipedia.org/wiki/Active_filtershttp://en.wikipedia.org/wiki/Oscillatorshttp://en.wikipedia.org/wiki/Triangle_wavehttp://en.wikipedia.org/wiki/Triangle_wavehttp://en.wikipedia.org/wiki/Triangle_wave8/3/2019 Ipg Iiitm Op Amp
9/42
Amplifiers
Differential Amplifier
Amplifies difference
between inputs
Single-ended Amplifier
Operational Amplifier: has a very high gain and widespreadapplications not limited to linear amplification system
but digital logic system as well.
8/3/2019 Ipg Iiitm Op Amp
10/42
Introduction
Operational Amplifiers are represented bothschematically and realistically below:
Active component!
8/3/2019 Ipg Iiitm Op Amp
11/42
introduction
IntroductionThe operational amplifier or op-amp is a circuit of
components integrated into one chip.
A typical op-amp is powered by two dc voltages and hasan 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
8/3/2019 Ipg Iiitm Op Amp
12/42
introduction
Op-amp Pins
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)
8/3/2019 Ipg Iiitm Op Amp
13/42
Sensor signals are often too weak or too noisy
Op-amps ideally increase the signal amplitude without
affecting its other properties
Why are they useful?
8/3/2019 Ipg Iiitm Op Amp
14/42
Ideal Op Amp
Zin is infinite
Zout is zero
Amplification (Gain) Vout / Vin =
Unlimited bandwidth
Vout = 0 when Voltage inputs = 0
8/3/2019 Ipg Iiitm Op Amp
15/42
introduction
Practical Operational AmplifiersAn 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.
8/3/2019 Ipg Iiitm Op Amp
16/42
Ideal Op Amp
Ideal Op-Amp Typical Op-Amp
Input Resistance infinity 106 (bipolar)
109 - 1012 (FET)
Input Current 0 10-12
10-8
AOutput Resistance 0 100 1000
Operational Gain infinity 105 - 109
Common Mode Gain 0 10-5
Bandwidth infinity Attenuates and phases at highfrequencies
Temperature independent Bandwidth and gain
8/3/2019 Ipg Iiitm Op Amp
17/42
introduction
Operational Amplifiers
8/3/2019 Ipg Iiitm Op Amp
18/42
introduction
Operational Amplifiers
Positive Saturationwhere the output
voltage exceeds the
positive power input
Negative Saturation
where the output
voltage would be less
than the negative powerinput
8/3/2019 Ipg Iiitm Op Amp
19/42
introduction
Operational Amplifiers
Linear Region where
the output voltage islinear based on A (gain)
8/3/2019 Ipg Iiitm Op Amp
20/42
application
Type of op-amp
There are 2 types of application in op-amp Linear application
Non-linear application
Linear application is where the op-amp operate in
linear region:
Assumptions in linear application:
Input current, Ii = 0
Input voltage: V+=V-
Feedback at the inverting input
8/3/2019 Ipg Iiitm Op Amp
21/42
application
Non-linear application is where the op-amp operate innon-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-
Types of op-amp
8/3/2019 Ipg Iiitm Op Amp
22/42
application
Applications of op-amp
Comparator Inverter
Audio amplifier
Signal Modulation
Filters
Voltage-Current signal conversion
Mathematical Operations
8/3/2019 Ipg Iiitm Op Amp
23/42
application
Inverting Amplifier
Non-Inverting Amplifier
Summing Amplifier
Unity Follower Difference Amplifier
Integrators
Differentiators
Op-amp Circuit Application
8/3/2019 Ipg Iiitm Op Amp
24/42
application
Design and Analysis ofOp-amp Circuit
8/3/2019 Ipg Iiitm Op Amp
25/42
Chap 0 25
Transfer Function: Ideal Op-amps
Transfer Function = Output / Input
Voltage Amp TF (Gain):
Usually Av 1
Op-amp is preferred because:
Easy to use in circuit designed compared to
discrete Transistor circuits
o
v
i
vA
v
8/3/2019 Ipg Iiitm Op Amp
26/42
Chap 0 26
Ideal Op-amps
Assumptions
Open loop Gain = Infinity
Input Impedance Rd = Infinity
Output Impedance Ro = 0 Bandwidth = Infinity
Infinite Frequency Response
vo=0 when v1 = v2
No Offset Voltage
8/3/2019 Ipg Iiitm Op Amp
27/42
Chap 0 27
Ideal Op-amps (Cont.)
Notev0 = A(v2 v1)
If v0 = , A = (Typically 100,000)
Then v2 v1 = 0 v2 = v1
Since v2 = v1 and Rd = We can neglect the current in Rd
Rule 1
When the Op-amp is in linear range the two inputs are
at the same voltage
Rule 2
No Current flows into either terminal of the Op-amp
8/3/2019 Ipg Iiitm Op Amp
28/42
application:inverting amplifier
Application: Inverting amplifier
Provide a constant gain multiplier
Input signal is connected to the inverting inputof the op-amp. Therefore, the output signal is180 degree out of phase from the input signal
Rf is the feed-back resistor to control thevoltage gain of the op-amp
8/3/2019 Ipg Iiitm Op Amp
29/42
29
Inverting Amplifier
From Rule 1
v- = v+ = 0
From Rule 2 & KCL
ii + if= 0 ii = -ifFrom Ohms law
ii = vi / Ri , , if= vo / Rfvi / Ri = - vo / Rfvo / vi = -Rf/ Ri
Inverting Amp Gain
-Rf/ Ri
Inverting Amp with Gain= - Rf/ Ri
Virtual Ground
8/3/2019 Ipg Iiitm Op Amp
30/42
Non-inverting configuration
1
2
21
21
21
1
0
;
0:
;0
:
R
RVV
R
VV
R
V
VVinsert
R
VV
R
Vso
Iwhile
III
KCLuse
VVV
io
oii
i
o
i
i
i
Vi
I1
I2
Ii
8/3/2019 Ipg Iiitm Op Amp
31/42
application:inverting amplifier
Summary of op-amp behavior
Vo = A(V+ - V )
Vo/A = V+ - V
Let A infinity
then,
V+
- V 0
8/3/2019 Ipg Iiitm Op Amp
32/42
application:summing amplifier
Application: Summing amplifier
Virtual-ground equivalent circuit.
8/3/2019 Ipg Iiitm Op Amp
33/42
Summing Amplifier
V1
V2
V3
R1
R2
R3
Rf
This circuit is called
a weighted summer
3
3
2
2
1
1
3
3
2
2
1
1
3
3
2
2
1
1
321
;0
:
;0
:
0
R
V
R
V
R
VRV
R
V
R
V
R
V
R
V
Vinsert
R
VV
R
VV
R
VV
R
VVso
Iwhile
IIIII
KCLuse
VV
fo
f
o
f
o
i
RfiRRR
8/3/2019 Ipg Iiitm Op Amp
34/42
application:difference amplifier
Application: Difference amplifier
)( 212
4 VVR
R
VO
43
21
RR
RR
8/3/2019 Ipg Iiitm Op Amp
35/42
application:integrator
Application: Integrator
Feedback component = capacitor :
Integrator
I IC
dttvRC
tv
dt
tdvC
R
tv
III
io
i
Ci
)(1
)(
)(0
)(0
sC
1
Cj
1X
:impedancecetanCapaci
C
8/3/2019 Ipg Iiitm Op Amp
36/42
application:differentiator
Application: Differentiation
dt
tdvRCtv
R
tvV
dt
tdv
C
II
io
oi
RC
)()(
)()(
8/3/2019 Ipg Iiitm Op Amp
37/42
Chap 0 37
Unity-Gain Amplifier
Gain of Unity-Gain
Op-amp is 1 Vo = Vi
Applications
Buffer amplifier
Isolate one circuit from
the loading effects of a
following stage
Impedance converter
Data conversion System
(ADC or DAC) whereconstant impedance or
high impedance is
required
8/3/2019 Ipg Iiitm Op Amp
38/42
non-linear application
Non-linear application is where the op-amp operate 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
8/3/2019 Ipg Iiitm Op Amp
39/42
non-linear application:comparator
Non-linear application: Comparator
8/3/2019 Ipg Iiitm Op Amp
40/42
non-linear application:comparator
Non-linear application: Comparator
Vo(V)
10
-5
t
VS(V)
t
Compare V+ and V-
V+=0
V-
=VS
When:VS>0,V
+>V- so Vo=10VVS
8/3/2019 Ipg Iiitm Op Amp
41/42
non-linear application:schmitt trigger
Non-linear application
Schmitt Trigger
-
+
O
fVRR
RV
1
1
Positive Feedback
8/3/2019 Ipg Iiitm Op Amp
42/42
VV
VtVVandVVstateinitialwith
VVVandRRassume
VRR
RV
S
o
EECCf
O
f
5.7)15(2
1
sin1015
151
1
1
Non-linear application
Schmitt 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