Op-Amp

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

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

Introduction

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.

AND……. 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

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

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

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

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)

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

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

0n

f s

o s

f s

fo s

s

i

i i

v v

R R

Rv v

R

Closed loop Inverting amplifier

0

i i is f n

v vn p

vsi

s Rsvoi

f Rf

“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

Closed loop non-Inverting amplifier

“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

sn p g o

s f

s fo g

s

fo g

s

v v

Rv v v v

R R

R Rv v

R

Rv v

R

Vd

+

Vo

+Vcc=+5V

Vcc= 5V

0

+5V

5V

Distortion

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.

Few applications of op-ampSUMMER OR ADDER CKT

Uses: Add multiple sensors inputs

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

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