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Operational Amplifiers Introduction & History Basic Structure & ckt of Op-Amp Types of Operational Amplifier Comparison between Ideal & Practical
Operational Amplifier Inverting and Non-Inverting OP-amp Other Useful Circuits Op-amp based Daily life Devices with
their circuit diagram.
Operational AmplifierAn active circuit element designed to perform
mathematical operations like addition, subtraction, multiplication, division, differentiation and integration. known as OP-amp.
_
+
Key Points:-Operational amplifiers are among the most widely used building blocks in electronic circuitsAn ideal operational amplifier would have infinite voltage gain, infinite input resistance and zero output resistanceDesigners often make use of cookbook circuitsReal op-amps have several non-ideal characteristics However, if we choose components appropriately this should not affect the operation of our circuitsFeedback allows us to increase bandwidth by trading gain against bandwidthFeedback also allows us to alter other circuit characteristics
HistoryOperational Amplifier is invented
by Karl D. Swartzel Jr. 1941-First Production 1952 -Philbrick Operational
Amplifiers (marketed by George A. Philbrick) were constructed with vacuum tubes
1965-Philbrick Op-amp Used in analog computers.
vacuum tube operational amplifiers were still in use and cost in the range of $75.
Some reports say that Loebe Julie actually
developed the operational amplifier circuitry.
• i(+), i(-) : Currents into the amplifier on the inverting and noninverting lines respectively
• vid : The input voltage from inverting to non-inverting inputs
• +VS , -VS : DC source voltages, usually +15V and –15V• Ri : The input resistance, ideally infinity• A : The gain of the amplifier. Ideally very high, in the
1x1010 range.• RO: The output resistance, ideally zero• vO: The output voltage; vO = AOLvid where AOL is the
open-loop voltage gain
The Operational Amplifier+VS
-VS
vid
Inverting
Noninverting
Output
+
_i(-)
i(+)
vO = Advid
ROARi
Basic Structure of OP-Amp
Input Stage
Intermediate Stage
Level Shifting Stage
Output
Stageinput Outpu
t
Dual input Balanced
output Differential Amplifier
Dual Input unbalanced output
Differential Amplifier
Emitter follower
using constant current Source
Push-pull
Amplifier
Complete circuit of an OP-amp
Types of OP-am
pon the basis of purpose &
Application
General purpose op-amp
Special purpose op-amp
General purpose operational Amplifiers may be used for variety of applications such as
Adding signals Subtracting signals integrating signalsExample:- µA 741 & 351
Special purpose operational Amplifier are used only for specific application such as
Audio Power Application High voltage Application Low Noise ApplicationExample:- LM380 & 1641
The Four Amplifier Types
Description Gain Symbol
Transfer Function
Voltage Amplifieror
Voltage Controlled Voltage Source (VCVS)
Av vo/vin
Current Amplifieror
Current Controlled Current Source (ICIS)
Ai io/iin
Transconductance Amplifieror
Voltage Controlled Current Source (VCIS)
gm(siemens) io/vin
Transresistance Amplifieror
Current Controlled Voltage Source (ICVS)
rm(ohms) vo/iin
IC Product• A single package will often contain several op-amps [DIP 741] [Dual op-amp 1458 device]
Ref:080114HKN Operational Amplifier
Ideal Vs Practical Op-AmpIdeal Practical
Open Loop gain A 105
Bandwidth BW 10-100HzInput Impedance Zin
>1M
Output Impedance Zout
0 10-100
Output Voltage Vout Depends only on Vd = (V+V)Differential mode signal
Depends slightly on average input Vc = (V++V)/2 Common-Mode signal
CMRR 10-100dB
+
~AVin
Vin VoutZout=0
Ideal op-amp
+
AVinVin Vout
Zout~
Zin
Practical op-amp
An Ideal Operational Amplifier An ideal op-amp would be an ideal voltage amplifier and
would have: Av = , Ri = and Ro = 0
Equivalent circuit of an ideal op-amp
Basic Operational Amplifier Circuits
Inverting and non-inverting amplifiers
A non-inverting amplifierAnalysis
Since the gain is assumed infinite, if Vo is finitethen the input voltage must be zero. Hence
Since the input resistance of the op-amp is
and hence, since V– = V+ = Vi
and 21
2RR
RVV o
21
2RR
RVV oi
2
21RRR
VVGi
o
iVVV
An inverting amplifierAnalysis
Since the gain is assumed infinite, if Vo is finite the input voltage must be zero. Hence
Since the input resistance of the op-amp is
its input current must be zero, and hence
Now
0 VV
21 II
1111
0RV
RV
RVVI ooo
2222
0RV
RV
RVVI iii
Analysis (continued)Therefore, since I1 = -I2
or, rearranging
Here V– is held at zero volts by the operation of the circuit, hence the circuit is known as a virtual earth circuit
21 RV
RV io
2
1RR
VVGi
o
Some of the Daily Life Devices Where Op-Amp is used:-
Op-Amps have many applications and can be used when a signal needs to be modified, amplified or compared.
In the Next few Slides Some of the Op-amp based Devices with there circuit Diagram is shown .
+-
1
2
3
4 5
6
7
8
GND Out
+ V
Gain
- IN Bypass
+ IN
+Gain
Maximum RatingsSupply Voltage ±15 VPower Dissipation 660 mWInput Voltage ±.4 VOperating Temperature 0°C to 70°C
CharacteristicsInput Resistance 50 kΩCMMR 70 to 90 dBBandwidth 300 kHzTotal Harmonic Distortion 0.2%
+-
+-
+-
+-
In
R1
R1
R1
R1
R1
R1
R1
R1
R2+V
-V+V + - + -
LED
LED
LED
LED
R1
R1
R1 R1
R1
+
-
Source 1
Source 2
Source 3Out
Operational Amplifier
+
vi
Ra
vov-
v+
Rf
+
vi
Ra
vov-
v+
Rf
R2R1
+
vi vov-
v+
Rf
+
vivov-
v+
Rf
R2R1
Noninverting amplifier
Noninverting input with voltage divider
ia
fo v
RRR
RR
v ))(1(21
2
Voltage follower
io vv
ia
fo v
RR
v )1(
Less than unity gain
io vRR
Rv21
2
In addition to simple amplifiers op-amps can also be used in a range of other circuits.1. Unity gain buffer amplifier2. Current to voltage converter3. Differential amplifier (or subtractor)4. Inverting summing amplifier. etc
Extra But Important Open-Loop Op Amp Characteristics
Device LM741C LF351 OP-07 LH0003 AD549K
Technology BJT BiFET BJT Hybrid BJT BiFET
AOL(typ) 200 k 100 k 400 k 40 k 100 k
Rin 2 M 1012 8 M 100 k 1013 || 1 pF
Ro 50 30 60 50 ~100
SR 0.5 V/s 13 V/s 0.3 V/s 70 V/s 3 V/s
CMRR 90 dB 100 dB 110 dB 90 dB 90 dB
Sources:- Dailey, Denton. Electronic Devices and Circuits, Discrete
and Integrated. Prentice Hall, New Jersey: 2001. (pp 456-509)
1Table 12.1: Selected Op Amps and Their Open Loop Characteristics, pg 457
Liou, J.J. and Yuan, J.S. Semiconductor Device Physics and Simulation. Plenum Press, New York: 1998.
Web Sources www.infoplease.com/ce6/sci/A0803814.html http://www.infoplease.com/ce6/sci/A0836717.html http://people.msoe.edu/~saadat/PSpice230Part3.htm http://en.m.wikipedia.org/wiki/operational_amplifier? http://www.electronics-tutorials.ws/opamp/ http://www.ti.com
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