Opamp Intro

8/3/2019 Opamp Intro

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introduction

Chapter 5:

Operational Amplifiers


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introduction

Introduction

The operational amplifier or op-amp is a circuit ofcomponents integrated into one chip.

A typical op-amp is powered by two dc voltagesand has an inverting(-) and a non-inverting input(+) and an output.

An op amp is an electronic device which provides

a voltage output based on the voltage input


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introduction

Basic op-amp

Op-amp has two inputs that connect to two terminalsand one output


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introduction


Five important pins

2 The inverting input

3 The non-inverting input

6 The output

4 The negative power supply V- (-Vcc)

7 The positive power supply V+ (+Vcc)


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introduction


The output of the op amp is given by the followingequation:

Vd = E1 E2and Vo = AVOL(Vd)

AVOL is called the open-loop voltage gain because itis the gain of the op amp without any external feedbackfrom output to input


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introduction


Positive Saturationwhere the outputvoltage exceeds thepositive power input


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introduction


Linear Regionwhere the outputvoltage is linearbased on A (gain)


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introduction



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introduction

What do they really look like?


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introduction

IC Circuit


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introduction



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introduction


An ideal op-amp has infinite gain and bandwidth,

we know this is impossible.However, op-amps do have:

very high gain

very high input impedance(Zin= )

very low output impedance (Zout = 0)

wide bandwidth.


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application

Application in op-amp

There are 2 types of application in op-amp

Linear application

Non-linear application

Linear application is where the op-amp operatein linear region:

Assumptions in linear application:

Input current, Ii = 0

Input voltage: V+=V-

Feedback at the inverting input


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application

Non-linear application is where the op-ampoperate in non-linear region

By comparing these two input voltages:positive input voltages, V+ and negative input

voltage, V- where:

VO = VCC if V+ > V-

VO = -VEE if V+ < V-


Application in op-amp


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application

Applications of op-amp

Comparator

Inverter

Audio amplifier

Difference Amplifier Filter

Summing Amplifier


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application

Inverting Amplifier

Non-Inverting Amplifier

Summing Amplifier

Unity Follower Difference Amplifier

Integrators

Differentiators

Op-amp Circuit Application


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application:inverting amplifier

Application: Inverting amplifier

Provide a constant gain multiplier

Input signal is connected to the inverting input of the op-

amp. Therefore, the output signal is 180 degree out ofphase from the input signal

Rf is the feed-back resistor to control the voltage gain ofthe op-amp


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Summary of op-amp behavior

Vo = A(V+ - V)

Vo/A = V+ - V

Let A infinity

then,

V+ - V 0


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V+ = V

I+ = I = 0

Seems strange, but the input terminals to anop-amp act as a short and open at the same time

Summary of op-amp behavior


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To analyze an op-amp circuit for linearoperation

Write node equations at + and - terminals

(Ii=I+ = I-= 0)

Set V+ = V-

Solve for Vo


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Analysis of inverting amplifier

I1

If

Ii

V = 0Ii= 0

I1= If Ii

Vs

V

R1

=

V

Vo

Rf

V

= V = 0

Vo

Vs

=-R

f

R1

Vo=-

Rf

R1

Vs


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application:non-inverting amplifier

Application:Non-inverting amplifier


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Non-inverting configuration

Vi= V = V

use KCL :

I1= I

iI2

while Ii= 0

;

so :0 V

R1

=

V Vo

R2

insert V

= Vi ;

0 Vi

R1

=

Vi V

o

R2

Vo= V

i1

R2

R1

Vi

I1

I2

Ii


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application:summing amplifier

Application: Summing amplifier

Virtual-ground equivalent circuit.


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Summing Amplifier

V1

V2

V3

R1

R2

R3

Rf

This circuit is calle

a weighted summer

V = V

= 0

use KCL :

IR1 IR2 IR3= Ii IRf

while Ii= 0 ;

so:V

1 V

R1

V2 V

R2

V3 V

R3

=

V

Vo

Rf

insert V

= 0 ;

V1

R1

V2

R2

V3

R3

=

Vo

Rf

Vo= R

f

V1

R1

V2

R2

V3

R3


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application:unity-follower

Application: Unity Follower

VO=

V1


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application:difference amplifier

Application:Difference amplifier

VO

=

R4

R2

V1

V2

R1= R

2

R3= R

4

A li i


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application:instrumentation amplifier

Application:Instrumentation Amplifier

R2

Buffer

R2

R1

R1

RA

RB

RA

Difference amplifier

VO=

R2

R1

12R A

RB

V2

V1

R2


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application:integrator

Application:Integrator

Feedback component = capacitor : Integrator

I IC

I= Ii ICv i t

R

= 0 Cdv0 t

dtv o t =

1

RC vi t dt

Capaci tan ce impedance :

XC=1

jC=

1

sC


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application:differentiator

Application:Differentiation

IC= IR

Cdv i t

dt

=

V vo t

R

v o t = RCdv i t

dt


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exercise

Exercise 1

Find VO?


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exercise

Exercise 2

Find V2 and V3?


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exercise

Exercise 3

Find VO?


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exercise

Exercise 4

Find VO?


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non-linear application

Non-linear application is where the op-ampoperate in non-linear region

By comparing these two input voltages:positive input voltages, V+ and negative input

voltage, V- where:VO = VCC if V

+ > V-

VO = -VCC if V+ < V-


Recall: Non-linear application in op-amp

Non linear application:


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non-linear application:comparator

Non-linear application:Comparator

Non-linear application:


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non-linear application:comparator

Non-linear application:Comparator

Vo(V)

10

-5

t

VS(V)

t

Compare V+ and V-

V+=0V-=VS

When:VS>0,V

+>V- so Vo=10VVS


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non-linear application:schmitt trigger

Non-linear applicationSchmitt Trigger

-

+

V =R 1

R1 R fVO

Positive Feedback

Non-linear application


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non-linear application:schmitt trigger

V =R1

R1

RfV

O

assume R1= R f and VCC= VEE= 15 V

with initial state Vo= 15 V and

VS=

V=

10 sin t V

V =1

215 = 7 . 5 V

Non linear applicationSchmitt Trigger

Vo(V)

15

-15

t

VS(V)

t

7.5

-7.5

Vo(V)

VS(V)-7.5 7.5-10 10

15

-15

(a) Transfer Characteristic of Schmitt Trigger

(c) Output Voltage of Schmitt Trigger

(b) Input Voltage of Schmitt Trigger

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Opamp Intro