Ipg Iiitm Op Amp

8/3/2019 Ipg Iiitm Op Amp

1/42

1

Basic Electrical Engineering

Operational Amplifier


2/42

Operational Amplifiers

An operational amplifier (op-amp) is a DC-coupledhigh-gain electronic voltage amplifier with a differential

inputs and a single-ended output.

An op-amp produces an output voltage that is typicallyhundreds of thousands times larger than the voltage

difference between its input terminals.

They had their origins in analog computers where they

were used in many linear, non-linear and frequency-

dependent electrical and electronics circuits.


3/42

Background

Originally invented in early 1940s using vacuum tubetechnology

Initial purpose was to execute math operations in

analog electronic calculating machines

Small in size with invention of transistor Now made on integrated circuit (IC)

Only most demanding applications use discrete

components

Huge variety of applications, in electrical andelectronics ckts, low cost, and ease of mass production

make them extremely popular


4/42

Op-amp Circuit notation

The circuit symbol for an op-amp :

V+: non-inverting input

V-: inverting input

Vout: output

Vs+ or Vcc+: positive power supply

Vs- or Vcc-: : negative power supply
http://en.wikipedia.org/wiki/File:Op-amp_symbol.svg


5/42

Op-amp: Operation

The amplifier's differential inputs consist of a V+

input and

a V- input, and ideally the op-amp amplifies only the

difference in voltage between the two, which is called

the differential input voltage. The output voltage of the

op-amp is given by the equation

Vout = (V+ - V-) AOL

AOL is the open loop gain of the amplifier.

The magnitude ofAOL

is typically very large for Integrated

Circuit (IC) op-amps and therefore even a quite small

difference between and drives the amplifier output

nearly to the supply voltage. This is called saturation of

the amplifier.
http://en.wikipedia.org/wiki/File:Op-amp_open-loop_1.svg


6/42

Input offset voltageVoltage required across the op-amp's input terminals to

drive the output voltage to zero, is related to themismatches in input bias current.

In the perfect amplifier, there would be no input offset

voltage. However, it exists in actual op-amps because

of imperfections in the differential amplifier:Input offset voltage creates two problems:

1. due to the amplifier's high voltage gain, it virtually

assures that the amplifier output will go into

saturation if it is operated without negative feedback.2. In a closed loop, negative feedback configuration, the

input offset voltage is amplified along with the signal.


7/42

Common-mode gain

A perfect operational amplifier amplifies only the voltage

difference between its two inputs, completely rejectingall voltages that are common to both.

However, the differential input stage of an operational

amplifier is never perfect, leading to the amplification

of these identical voltages to some degree. Thestandard measure of this defect is called the common-

mode rejection ratio (denoted CMRR). Minimization of

common mode gain is usually important in non-

inverting amplifiers that operate at high amplification.
http://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratiohttp://en.wikipedia.org/wiki/Common-mode_rejection_ratio


8/42

Positive feedback applications

which takes a fraction of the output signal back to thenon-inverting input.

Application: Comparator with hysteresis, the Schmitt

trigger.

Some circuits may use Positive feedback and Negativefeedback around the same amplifier, for example

Triangle wave oscillators and active filters.
http://en.wikipedia.org/wiki/Triangle_wavehttp://en.wikipedia.org/wiki/Oscillatorshttp://en.wikipedia.org/wiki/Active_filtershttp://en.wikipedia.org/wiki/Active_filtershttp://en.wikipedia.org/wiki/Active_filtershttp://en.wikipedia.org/wiki/Active_filtershttp://en.wikipedia.org/wiki/Oscillatorshttp://en.wikipedia.org/wiki/Triangle_wavehttp://en.wikipedia.org/wiki/Triangle_wavehttp://en.wikipedia.org/wiki/Triangle_wave


9/42

Amplifiers

Differential Amplifier

Amplifies difference

between inputs

Single-ended Amplifier

Operational Amplifier: has a very high gain and widespreadapplications not limited to linear amplification system

but digital logic system as well.


10/42

Introduction

Operational Amplifiers are represented bothschematically and realistically below:

Active component!


11/42

introduction

IntroductionThe operational amplifier or op-amp is a circuit of

components integrated into one chip.

A typical op-amp is powered by two dc voltages and hasan 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


12/42

introduction

Op-amp Pins

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)


13/42

Sensor signals are often too weak or too noisy

Op-amps ideally increase the signal amplitude without

affecting its other properties

Why are they useful?


14/42

Ideal Op Amp

Zin is infinite

Zout is zero

Amplification (Gain) Vout / Vin =

Unlimited bandwidth

Vout = 0 when Voltage inputs = 0


15/42

introduction

Practical Operational AmplifiersAn 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.


16/42

Ideal Op Amp

Ideal Op-Amp Typical Op-Amp

Input Resistance infinity 106 (bipolar)

109 - 1012 (FET)

Input Current 0 10-12

10-8

AOutput Resistance 0 100 1000

Operational Gain infinity 105 - 109

Common Mode Gain 0 10-5

Bandwidth infinity Attenuates and phases at highfrequencies

Temperature independent Bandwidth and gain


17/42

introduction



18/42

introduction


Positive Saturationwhere the output

voltage exceeds the

positive power input

Negative Saturation

where the output

voltage would be less

than the negative powerinput


19/42

introduction


Linear Region where

the output voltage islinear based on A (gain)


20/42

application

Type of op-amp

There are 2 types of application in op-amp Linear application

Non-linear application

Linear application is where the op-amp operate in

linear region:

Assumptions in linear application:

Input current, Ii = 0

Input voltage: V+=V-

Feedback at the inverting input


21/42

application

Non-linear application is where the op-amp operate innon-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-

Types of op-amp


22/42

application

Applications of op-amp

Comparator Inverter

Audio amplifier

Signal Modulation

Filters

Voltage-Current signal conversion

Mathematical Operations


23/42

application

Inverting Amplifier

Non-Inverting Amplifier

Summing Amplifier

Unity Follower Difference Amplifier

Integrators

Differentiators

Op-amp Circuit Application


24/42

application

Design and Analysis ofOp-amp Circuit


25/42

Chap 0 25

Transfer Function: Ideal Op-amps

Transfer Function = Output / Input

Voltage Amp TF (Gain):

Usually Av 1

Op-amp is preferred because:

Easy to use in circuit designed compared to

discrete Transistor circuits

o

v

i

vA

v


26/42

Chap 0 26

Ideal Op-amps

Assumptions

Open loop Gain = Infinity

Input Impedance Rd = Infinity

Output Impedance Ro = 0 Bandwidth = Infinity

Infinite Frequency Response

vo=0 when v1 = v2

No Offset Voltage


27/42

Chap 0 27

Ideal Op-amps (Cont.)

Notev0 = A(v2 v1)

If v0 = , A = (Typically 100,000)

Then v2 v1 = 0 v2 = v1

Since v2 = v1 and Rd = We can neglect the current in Rd

Rule 1

When the Op-amp is in linear range the two inputs are

at the same voltage

Rule 2

No Current flows into either terminal of the Op-amp


28/42

application:inverting amplifier

Application: Inverting amplifier

Provide a constant gain multiplier

Input signal is connected to the inverting inputof the op-amp. Therefore, the output signal is180 degree out of phase from the input signal

Rf is the feed-back resistor to control thevoltage gain of the op-amp


29/42

29

Inverting Amplifier

From Rule 1

v- = v+ = 0

From Rule 2 & KCL

ii + if= 0 ii = -ifFrom Ohms law

ii = vi / Ri , , if= vo / Rfvi / Ri = - vo / Rfvo / vi = -Rf/ Ri

Inverting Amp Gain

-Rf/ Ri

Inverting Amp with Gain= - Rf/ Ri

Virtual Ground


30/42

Non-inverting configuration

1

2

21

21

21

1

0

;

0:

;0

:

R

RVV

R

VV

R

V

VVinsert

R

VV

R

Vso

Iwhile

III

KCLuse

VVV

io

oii

i

o

i

i

i

Vi

I1

I2

Ii


31/42

application:inverting amplifier

Summary of op-amp behavior

Vo = A(V+ - V )

Vo/A = V+ - V

Let A infinity

then,

V+

- V 0


32/42

application:summing amplifier

Application: Summing amplifier

Virtual-ground equivalent circuit.


33/42

Summing Amplifier

V1

V2

V3

R1

R2

R3

Rf

This circuit is called

a weighted summer

3

3

2

2

1

1

3

3

2

2

1

1

3

3

2

2

1

1

321

;0

:

;0

:

0

R

V

R

V

R

VRV

R

V

R

V

R

V

R

V

Vinsert

R

VV

R

VV

R

VV

R

VVso

Iwhile

IIIII

KCLuse

VV

fo

f

o

f

o

i

RfiRRR


34/42

application:difference amplifier

Application: Difference amplifier

)( 212

4 VVR

R

VO

43

21

RR

RR


35/42

application:integrator

Application: Integrator

Feedback component = capacitor :

Integrator

I IC

dttvRC

tv

dt

tdvC

R

tv

III

io

i

Ci

)(1

)(

)(0

)(0

sC

1

Cj

1X

:impedancecetanCapaci

C


36/42

application:differentiator

Application: Differentiation

dt

tdvRCtv

R

tvV

dt

tdv

C

II

io

oi

RC

)()(

)()(


37/42

Chap 0 37

Unity-Gain Amplifier

Gain of Unity-Gain

Op-amp is 1 Vo = Vi

Applications

Buffer amplifier

Isolate one circuit from

the loading effects of a

following stage

Impedance converter

Data conversion System

(ADC or DAC) whereconstant impedance or

high impedance is

required


38/42

non-linear application

Non-linear application is where the op-amp operate 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-

Input current, Ii = 0

Recall: Non-linear application in op-amp


39/42

non-linear application:comparator

Non-linear application: Comparator


40/42

non-linear application:comparator

Non-linear application: Comparator

Vo(V)

10

-5

t

VS(V)

t

Compare V+ and V-

V+=0

V-

=VS

When:VS>0,V

+>V- so Vo=10VVS


41/42

non-linear application:schmitt trigger


Schmitt Trigger

-

+

O

fVRR

RV

1

1

Positive Feedback


42/42

VV

VtVVandVVstateinitialwith

VVVandRRassume

VRR

RV

S

o

EECCf

O

f

5.7)15(2

1

sin1015

151

1

1


Schmitt 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

Ipg Iiitm Op Amp

Documents

Transcript of Ipg Iiitm Op Amp