8/7/2019 ELE B35

1/7

INVERTING MODE OF OP AMPLIFIER

Saurabh Pandey , Roll.no-C4911B35, section-C4911 Lovely Professional University,Phagwara(Punjab) India

Abstract -In this term paper of electrical engineering of

topic inverting mode of op amplifier .I have studied

about the all inverting mode of op amplifier . Types of op

amplifier, its history how op amplifier are first formed ,

its concept of inverting mode of op amplifier where the

inverting mode of op amplifier are used .i have also

studied about limitation of inverting mode of op amplifier

The op amp is one of the basic building blocks of linear

design. In its classic form it consists of two input terminals,

one of which inverts the phase of the signal, the other

preserves the phase, and an output terminal.

I. INTRODUCTION

he op amp is one of the basic building

blocks of linear design. In its classic form

it consists of two input terminals, one ofwhich inverts the phase of the signal, the other

preserves the phase, and an output terminal. The

standard symbol for the op amp is given in Figure 1.

This ignores the power supply terminals, which are

obviously required for operation.

T

I. Figure : Standard Op Amp Symbol

The name op amp is the standard abbreviation for

operational amplifier. This name comes from theearly days of amplifier design, when the op amp

was used in analog computers. (Yes, the firs

computers were analog in nature, rather than

digital). When the basic amplifier was used with a

few external components, various mathematica

operations could be performed, such as addition

integration, etc. One of the primary uses of analog

computers was during World War II, when they

were used for plotting ballistic trajectories.

8/7/2019 ELE B35

2/7

II. IDEAL VOLTAGE FEEDBACK

(VFB) MODEL

The classic model of the ideal voltage feedback

(VFB) op amp has the following

characteristics:

I. Infinite input impedance

II. Infinite bandwidth

III. Infinite voltage gain

IV. Zero output impedance

V. Zero power consumption

This is referred to as the voltage feedback

(VFB) model. This type of op amp comprises

nearly all op amps below 10 MHz bandwidth

and on the order of 90% of those with higher

bandwidths.

I. The attributes of an ideal VFB op amp

are summarized in Figure 2.

IDEAL OP AMP ATTRIBUTES

I. Infinite Differential Gain

II. 2. Zero Common Mode Gain

III. 3. Zero Bias Current

IV. 4. Infinite Bandwidth

V. OP AMP INPUT ATTRIBUTES

I. Infinite Impedance

II. Zero Bias CurrentIII. Respond to Differential Voltages

IV. Do Not Respond to Common Mode

Voltages

OP AMP OUTPUT ATTRIBUTES

I. Zero Impedance

II. BASIC OPERATION

The basic operation of the ideal op amp can be

easily summarized. First, we assume that there is a

portion of the output that is fed back to the inverting

terminal to establish the fixed gain for the amplifier

This is negative feedback. Any differential voltage

across the input terminals of the op amp is

multiplied by the amplifiers open loop gain which

is infinite for the ideal op amp. If the magnitude of

this differential voltage is more positive on the

inverting () terminal than on the non-inverting (+)

terminal, the output will swing negative. If the

magnitude of the differential voltage is more

positive on the non-inverting (+) terminal than on

the inverting () terminal, the output voltage will

swing positive. The infinite open loop gain of theamplifier will attempt to force the differential input

voltage to zero. As long as the inputs and output

stays in the operational range of the amplifier, it

will keep the differential input voltage at zero, and

the output will be the input voltage multiplied by

the gain determined by the feedback network

8/7/2019 ELE B35

3/7

I. OPERATIONAL AMPLIFIERS

An operational amplifier, or op-amp, is a very

high gain differential amplifier with

high input impedance and low output impedance.

Typical uses of the operational amplifier are to provide voltage amplitude changes (amplitude

and polarity), oscillators,

filter circuits, and many types of instrumentation

circuits. An op-amp contains a number

of differential amplifier stages to achieve a very

high voltage gain.

The earliest operational amplifier, or op-amp, was

invented in 1948 by George Philbrick. It was labeled

the uA-709, and was in vacuum tube form. The

original intent of the op-amp was to perform

mathematical operations in analog computers. The

op-amp is one of the most powerful integrated

circuits devices on the market because its circuit

transfer function (Vout/Vin) is entirely controlled by

the feedback network between output and input

II. Equivalent circuit of operational

amplifier

An Operational amplifier ("op-amp") is a DC-

coupled high-gain electronic voltage amplifier with

a differential input and, usually, a single-ended

output. An op-amp produces an output voltage that

is typically hundreds of thousands times larger than

the voltage difference between its input terminals

Initially, the cost of an op-amp was considerably

high. Averaging nearly 110 dollars, but hasdropped drastically in price since then. Most of

todays general-purpose op-amps cost only a few

dollars.

III. INVERTING AMPLIFIER

8/7/2019 ELE B35

4/7

The most widely used constant-gain amplifier

circuit is the inverting amplifier.. The output is

obtained by multiplying the input by a fixed or

constant gain, set by the input resistor (R1) and

feedback resistor (Rf)this output also being

inverted from the input.

Plus input terminal is grounded whereas the

external input signal Vin is applied to the inverting

or minus input terminal through resistance R1. A

feedback resistor Rf is connected from the output to

the inverting input terminal of the op-amp.

This arrangement provides a negative feedback

because any increase in output signal into the

inverting input, causing a decrease in the output

signal.

IV. Inverting mode of op-amps in ideal mode

In an inverting amplifier, the output voltage

changes in an opposite direction to the inputvoltage.

As for the non-inverting amplifier, we star

with the gain equation of the op-amp:

This time, V is a function of both Vout and Vin

due to the voltage divider formed by Rf andRin

Again, the op-amp input does not apply an

appreciable load, so:

Substituting this into the gain equation and

solving forVout:

IfAOL is very large, this simplifies to

8/7/2019 ELE B35

5/7

.

A resistor is often inserted between the non-

inverting input and ground (so both inputs

"see" similar resistances), reducing the input

offset voltage due to different voltage drops

due to bias current, and may reduce distortion

in some op-amps.

A DC-blocking capacitor may be inserted in

series with the input resistor when a frequency

response down to DC is not needed and any

DC voltage on the input is unwanted. That is,the capacitive component of the input

impedance inserts a DC zero and a low-

frequency pole that gives the circuit a band

pass or high-pass characteristics.

A GRAPH OF INVERTING AMPLIFIER

V in

Vou

A

8/7/2019 ELE B35

6/7

negative)power supply. Since the op amp will force

the differential voltage across the inputs to zero, theinverting input will also appear to be ground. In

fact, this node is often referred to as a virtual

ground.

If there is a voltage(VIN) applied to the input

resistor, It will set up a current(I1) through theresistor (RG) so that

Since the input impedence of the ideal op amp is

infinite, no current will flow into the invertinginput. Therefore, this same current(I1) must flow

through the feedback resistor(RF). Since the

amplifier will force the inverting terminal toground, the output will assume a votage(VOUT) such

that:

Doing some simple arithmetic then come to theconclusion that:

VII. APPLICATIONS

audio- and video-frequency pre-

amplifiers and buffers

voltage comparators

differential amplifiers

differentiators and integrators

filters

precision rectifiers

precision peak detectors

voltage and current regulators analog calculators

analog-to-digital converters

digital-to-analog converter

voltage clamps

oscillators and waveform generators

DC Millivoltmeter

AC Millivoltmeter

Display Driver

All of the op-amp configurations have one

thing in common: there exists a path from the

output of the op-amp back to its inverting

input. When the output is not railed to a

supply voltage, negative feedback ensures

that the op-amp operates in the linear region

(as opposed to the saturation region, where

the output voltage is saturated at one of the

supply

voltages).Amplification,addition/subtraction,

and integration/differentiation are all linear

operations. Note that both AC signals and

8/7/2019 ELE B35

7/7

DC offsets are included in these operations,

unless we add a capacitor in series with the

input signal(s) to block the DC component

VIII. CONCLUSION

In this term paper I have described aboutinverting mode of operational amplifier .We

have learned about the various types o

operational amplifier its uses its application

and its limitations .And many more

information regarding inverting mode o

operational amplifier

IX. REFERENCES

Foundations of Analog and Digital Electronic Circuits

By Anant Agarwal and Jefrey H. Lang

1. Electronic Devices and Circuits

By J.B.Gupta

2. Electronic Devices and Circuit Theory

By Boylestad and Nashelsky

3. http://en.wikipedia.org/wiki/Operational_amplifier

4. http://en.wikipedia.org/wiki/Operational_amplifier_applica

ions

5. http://www.electronics-radio.com/articles/analogue_circuits/operational-amplifier-

op-amp/inverting-amplifier.php

http://en.wikipedia.org/wiki/Operational_amplifierhttp://en.wikipedia.org/wiki/Operational_amplifier_applicationshttp://en.wikipedia.org/wiki/Operational_amplifier_applicationshttp://www.electronics-radio.com/articles/analogue_circuits/operational-amplifier-op-amp/inverting-amplifier.phphttp://www.electronics-radio.com/articles/analogue_circuits/operational-amplifier-op-amp/inverting-amplifier.phphttp://www.electronics-radio.com/articles/analogue_circuits/operational-amplifier-op-amp/inverting-amplifier.phphttp://en.wikipedia.org/wiki/Operational_amplifierhttp://en.wikipedia.org/wiki/Operational_amplifier_applicationshttp://en.wikipedia.org/wiki/Operational_amplifier_applicationshttp://www.electronics-radio.com/articles/analogue_circuits/operational-amplifier-op-amp/inverting-amplifier.phphttp://www.electronics-radio.com/articles/analogue_circuits/operational-amplifier-op-amp/inverting-amplifier.phphttp://www.electronics-radio.com/articles/analogue_circuits/operational-amplifier-op-amp/inverting-amplifier.php