introduction to operational amplifiers this slides helps u to know...what is op-amp...how it works...what are its uses...etc

1. Op-Amp

2. Contents
 Introduction
 Schematic And Realistic View
 Equivalent circuit of an op-amp
 Op-amp characteristics
 Ideal Op-Amp V/s Real Op-Amp
 Open loop Op-Amp
 Close loop Op-Amp
 Closed loop Inverting amplifier
 Closed loop non-Inverting amplifier
 Distortion
 Few applications of op-amp

3.  Full form of Op-Amp is “Operational amplifier”
 Op-Amp is called so, as previously they were used for
mathematical operations in analog computers.
 It is “Direct coupled high gain voltage amplifier”
 It uses differential amplifier which amplifies
difference between inputs

4. Op-Amp is….
 Solid state device capable of sensing and
amplifying the dc and ac input signals.
 Inexpensive, take up less space and
consume less power.
 Used in the field of communication,
computers, power and signal sources,
displays and measuring system.

5.  It Was introduced in 1940s.
 The most popular op-amp is 741 IC.
 IC version of op-amp make use of transistors,
with result in simple circuit designing.
 Modern op-amp works on lower voltage.
 Op Amps ideally increase the signal amplitude
without affecting its other properties

6. SCHEMATIC AND REALISTIC VIEW
» Pins (1,5) are control pin used to
eliminate the effects of internal
component voltages on the output of the
device

7. Equivalent circuit of an op-amp
From figure..
• Vin = (V+ - V-)
• G= Gain (Vout /Vin)
• Vout = G. Vin
• Rout must be low
• Rin must be high

8. Op-amp characteristics
Input offset voltage – Voltage which if applied to input
terminals, would reduce op-amp output voltage to zero.
Slew rate – Maximum rate at which output of op-amp can
change. It should be high.(volts/microseconds)
Open loop gain – Gain without feedback
CMRR(Common mode rejection ratio)-Ratio of
differential gain to common mode gain.
i.e.,
CMRR= Aid/ Acm

9. Ideal Op-Amp V/s Real Op-Amp
Ideal op-amps
 Infinite open-loop gain
 Infinite bandwidth
 Infinite slew rate
 Infinite input impedance
and so zero input current
 Zero input offset voltage
 Zero output impedance
 Zero noise
 Infinite Common-mode
rejection ratio (CMRR)
Real op-amps
 Finite open-loop gain
 Finite bandwidth
 Finite slew rate
 Finite input impedance and
so a little input current
 Small input offset voltage
 Small output impedance
 Small noise
 Finite Common-mode
rejection ratio (CMRR)

10. Open loop Op-Amp
(Op-amp without negative feedback)
+

Vo
~ Vi
+

Vo
~
Vi
• + terminal : Source
• – terminal : Ground
• 0o phase change
• + terminal : Ground
• – terminal : Source
• 180o phase change
Non-Inverting amplifier
Inverting amplifier
Gain is very high so unstable

11. Closed loop Op-Amp
(Op-amp with negative feedback)
Negative feedback weaken the input signal.
It reduces gain thus stability increases.
Reduction in nonlinear distortion.
Reduces effect of input offset voltage
Increase bandwidth

12. 0n
f s
o s
f s
f
o s
s
i
i i
v v
R R
R
v v
R

 
 
 
0
i i i
s f n
v v
n p
v
si
s R
s
v
oi
f R
f
 
 


“Virtual”
ground
This is closed
loop gain(Af)
and negative
sign shows
the inverted
o/p w.r.t i/p
Mag. Of o/p can be controlled by Rf
and RS

13. “Virtual”
ground
Closed loop
gain(Af) and
no phase
shift and gain
is always >1
Mag. Of o/p can be controlled by Rf
and RS
1

  



 
  
 
p g
s
n p g o
s f
s f
o g
s
f
o g
s
v v
R
v v v v
R R
R R
v v
R
R
v v
R

14. Vd
+

Vo
+Vcc=+5V
Vcc=5V
0
+5V
5V
The output voltage never excess the DC voltage
supply of the Op-Amp
When the output voltage is equal to or greater
than the supply voltage are referred to as
saturation of the amplifier which results in
distortion due to non-linear behavior.

15. Few applications of op-amp
Uses: Add multiple sensors inputs

16. COMPARATORS
Compares two Voltage and switches its output to indicate
which is larger.
Op-Amp operating in open-loop configuration (without
negative feedback) may be used as comparator.
Where Vs+ and Vs- are nominally the positive and negative
supply voltages

17. OP-AMP INTEGRATOR
Performs the mathematical operation of integration with
respect to time; that is, its output voltage is proportional to the
input voltage over time