Basic Block Diagram of OpAmp. V 1. Out put Stage (Buffer). Level Shifter. Gain Stage (C E Amp.). Input Stage (Diff. Amp.). I / P. V O. An OpAmp can be conveniently divided in to four main blocks An Input Stage or Input Diff. Amp. The Gain Stage The Level Translator An Out put Stage
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V1
Out put Stage (Buffer)
Level Shifter
Gain Stage (C E Amp.)
Input Stage
(Diff. Amp.)
I/P
VO
An OpAmp can be conveniently divided in to four main blocks
An Input Stage or Input Diff. Amp.
The Gain Stage
The Level Translator
An Out put Stage
Note: It can be used to perform various mathematical operations such as Addition, Subtraction, Integration, Differentiation, log etc.
V2
OpAmp IC
An ideal op amp has the following characteristics:
+VS
_
i()
Inverting
RO
A
vid
Output
Ri
vO = AdVid
Noninverting
i(+)
+
VS

Operational Amplifier ModelV1
Rout
Vout
Rin
Av(V1 V2)
V2
These Opamp circuits are commonly used:
Notice the output formula is similar to Inverting Amplifier, but they are not the same.
Because the opamp has a high input impedance the multiple inputs are treated as separate inputs.
Inverting Amplifier: Input and Output Resistances
Rout is found by applying a test current (or voltage) source to the amplifier output and determining the voltage (or current) after turning off all independent sources. Hence, vs= 0
But i1=i2
Since v = 0, i1=0. Therefore vo= 0 irrespective of the value of io.
Differential Amplifier Using Op Amp
I/P Current to op amp is zero
The UnityGain Amplifier or “Buffer”
Closedloop voltage gain
Used as a "line driver" that transforms a high input impedance (resistance) to a low output impedance. Can provide substantial current gain.
OpAmp Integrator Cont…
Since the inverting input is at virtual ground
Applying KCL at the inverting input
i1+i2 = 0
OpAmp Differentiator Cont…
Since the inverting input is at virtual ground
Applying KCL at the inverting input
i1+i2 = 0
Differentiators are avoided in practice as they amplify noise
NOTE
Combines 2 noninverting amplifiers with the difference amplifier to provide higher gain and higher input resistance.
Gain can be varied by varying single resistor R1
Ideal input resistance is infinite because input current to both op amps is zero. The CMRR is determined only by Op Amp 3.
Finite Openloop Gain and Gain Error
This is the “ideal” voltage gain of the amplifier. If Ab is not >>1, there will be “Gain Error”.
is called the feedback factor.
GE = (ideal gain)  (actual gain)
For the noninverting amplifier,
Output Voltage and Current Limits
Practical op amps have limited output voltage and current ranges.
Voltage: Usually limited to a few volts less than power supply span.
Current: Limited by additional circuits (to limit power dissipation or protect against accidental short circuits).
The current limit is frequently specified in terms of the minimum load resistance that the amplifier can drive with a given output voltage swing. Eg:
For the inverting amplifier,