Operational Amplifiers

introduction

Operational Amplifiers

introduction

Introduction The 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 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

introduction

Basic op-amp

Op-amp has two inputs that connect to two terminals and one output

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)

introduction


The output of the op amp is given by the following equation:

Vd = E1 – E2

and Vo = AVOL(Vd)

AVOL is called the open-loop voltage gain because it is the gain of the op amp without any external feedback from output to input

introduction


• Positive Saturation – where the output voltage exceeds the positive power input

introduction


• Linear Region – where the output voltage is linear based on A (gain)

introduction


• Negative Saturation – where the output voltage would be less than the negative power input

introduction


introduction

What do they really look like?

introduction

IC Circuit

introduction


introduction

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.

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 operate in linear region: Assumptions in linear application:

Input current, Ii = 0 Input voltage: V+=V-

Feedback at the inverting input

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 = -VEE if V+ < V-

Input current, Ii = 0

Application in op-amp

application

Applications of op-amp

Comparator Inverter Audio amplifier Difference Amplifier Filter Summing Amplifier

application

Inverting Amplifier Non-Inverting Amplifier Summing Amplifier Unity Follower Difference Amplifier Integrators Differentiators

Op-amp Circuit Application

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 of phase from the input signal

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


Summary of op-amp behavior

Vo = A(V+ - V−)

Vo/A = V+ - V−

Let A infinity

then,

V+ - V− 0


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


To analyze an op-amp circuit for linear operation

•Write node equations at + and - terminals

(Ii=I+ = I- = 0)

•Set V+ = V-

•Solve for Vo


Analysis of inverting amplifier

I1

If

Ii

€

V + = 0 Ii = 0

I1 = I f + Ii

Vs −V−

R1

= V − −Vo

Rf

V− =V + = 0

Vo

Vs

= −Rf

R1

Vo = −Rf

R1

Vs

application:non-inverting amplifier

Application:Non-inverting amplifier

Non-inverting configuration

+=

−=−=

−=−

=+=

==

−

−−

−+

1

2

21

21

21

1

0;

0:

;0

:

R

RVV

R

VV

R

VVVinsert

R

VV

R

Vso

Iwhile

III

KCLuse

VVV

io

oiii

o

i

i

i

Vi

I1

I2

Ii

application:summing amplifier

Application: Summing amplifier

Virtual-ground equivalent circuit.

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

VVinsert

R

VV

R

VV

R

VV

R

VVso

Iwhile

IIIII

KCLuse

VV

fo

f

o

f

o

i

RfiRRR

application:unity-follower

Application: Unity Follower

1VVO =

application:difference amplifier

Application: Difference amplifier

)( 212

4 VVR

RVO −=

43

21

RR

RR

==

application:instrumentation amplifier

Application: Instrumentation Amplifier

2RBuffer

2R

1R

1R

AR

BR

AR

Difference amplifier

( )121

2 21 VV

R

R

R

RV

B

AO −

+=

2R

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 =ω

=

application:differentiator

Application: Differentiation

dt

tdvRCtv

R

tvV

dt

tdvC

II

io

oi

RC

)()(

)()(

−=

−=

=−

exercise

Exercise 1

Find VO?

exercise

Exercise 2

Find V2 and V3?

exercise

Exercise 3

Find VO?

exercise

Exercise 4

Find VO?

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

non-linear application:comparator

Non-linear application: Comparator

Operational Amplifiers

Engineering

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