• Introduction• What is op-amp• Circuit symbol• Operational Amplifiers symbol• Pin Diagram• Important terms and equation• Ideal op-amp• Characteristics of op-amp • Ideal op-amp vs Real op-amp• Open Loop op-amp• Closed Loop op-amp• Applications of op-amp• Advantages & disadvantages

CONTENT

INTRODUCTION

The term “operational amplifier” denotes aspecial type of amplifier that, by proper selectionof its external components, could be configuredfor a variety of operations.

HISTORY First developed by John R. Ragazzine in 1947with vacuum tube.In 1960 at FAIRCHILD SEMICONDUCTORCORPORATION, Robert J. Widlar fabricated op-amp with the help of IC fabrication technology. In 1968 FAIRCHILD introduced the op-ampthat became become the industry standard.

An operational amplifier (op-amp) is a DC-coupled high-gain electronic voltage amplifier Direct- coupled high gain amplifier usually consisting of one or more differential amplifiersOutput stage is generally a push-pull or push-pullcomplementary-symmetry pair.

Op amps are differential amplifiers, and their output voltage is proportional to the difference of the two input voltages. The op amp's schematic symbol is shown in the above figure

Figure shows the symbol of op-amp & the power supply connections tomake it work. The input terminal identified by the ‘-’ and “+” symbols aredesignated inverting & non-inverting. Their voltage w.r.t ground aredenoted as VN & VP and output voltage as VO. Op-amp do not have a zerovolt ground terminal. Ground reference is established externally by thepower supply common.

Fig.. Ckt symbol for general purpose op-amp

Operational Amplifiers picture

Figure: The Philbrick Operational Amplifier.

Figure : What an Op-Amp

looks like in today's world

Op-amp pin diagram

There are 8 pins in a common Op-Amp,like the 741 which is used in manyinstructional courses.

Pin 1: Offset nullPin 2: Inverting input terminalPin 3: Non-inverting input

terminalPin 4: –VCC (negative voltage

supply)Pin 5: Offset nullPin 6: Output voltagePin 7: +VCC (positive voltage

supply)Pin 8: No Connection

Figure : Pin connection, LM741.

Vd

VN

Vp

V0

a = gain of amplifiers.Vd= difference between thevoltage.V0= gain of voltage.The equation :

V0 = a (VP -VN)

Electrical parameter :

•Input bias current(Ib): average of current that flows into theinverting and non-inverting input terminal of op-amp.•I/p and o/p impedance: It is the resistance offered by the inputsand the output terminals to varying voltages. The quantity isexpressed in Ohms.•Open Loop Gain: It is the overall voltage gain or the amplification.•Input offset voltage : It is a voltage that must be applied betweenthe two terminal of an op-amp to null the o/p.•Input offset current (Ii): The algebraic different between the currentin to the inverting and Non-inverting terminal.

Important terms and equation

Non -ideal op-amp

1. This is opposite to the ideal op-amp only the positive and Negative terminal have changed their position.

2. There is a single external input signal V1=V+ that is applied to the +Ve pin of op-amp.

3. A signal is also made to appear at the -Ve input terminal, But this is derived from resistors R1 and R2.

V1=V+

CHARACTERISTICS OF IDEAL OP-AMP

Infinite input impedance

Zero output impedance

Infinite voltage gain at low frequency

Infinite bandwidth

Infinite Common-mode rejection ratio

Infinite Power supply rejection ratio.

Characteristics of non ideal op-amp

Finite open-loop gain that causes gain error

Finite input impedance

Non zero output impedance

Finite CMRR

Common-mode input resistance

Finite bandwidth

Finite power supply rejection ratio.

Ideal Op-Amp V/s Real Op-Amp

Ideal op-amps

Infinite open-loop gain

Infinite bandwidth

Infinite slew rate

Infinite input impedanceand 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

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

f

o 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 Rs

voi

f Rf

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

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 f

o g

s

f

o g

s

v v

Rv v v v

R R

R Rv v

R

Rv v

R

APPLICATIONS

A to D Converters

Power source

Zero Crossing Detector (ZCD)

ADVANTAGES OF AN OP-AMP

1.OP-AMP is an universal amplifier2.Voltage comparators.3.Precision rectifiers.4.Analog to digital convertors.

DISADVANTAGES OF AN OP-AMP

• Most OP-AMP are Designed to for lowerpower operation.

• For high output desire then the OP-AMPspecifically designed for that purpose must beseen.

• Most commercial OP-AMP shuts off when theload resistance is below the specific level.