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UNIT-2 DESCRIPTIVE QUESTIONS

1. Write short notes on inverting am!i"ier#$OR% Derive the e&ression "or '!ose( !oo

gain o" an inverting am!i"ier.

An amplifier which provides a phase shift of 180obetween input and output is called

inverting amplifier.

The output voltage is feedback to inverting input terminal through Rf-R1network, where

Rfis the feedback resistor

nput signal !"i# is applied to the inverting terminal through R1. The non- inverting

terminal is grounded.

)N)*+SIS,

$ence negative sign indicates phase shift of 180o.

%ffective input impedance is R1.

R1should be large to avoid loading effect.

&suall' load resistor, R(is connected to prevent the reduction in gain.

The load current is given as

() "0* R(

f Rf+R1, the gain is greater than 1.

f RfR1, the gain is less than 1.

f Rf) R1, the gain is unit'.

f ) !ome constant#, the circuit is called S'a!e Changer.

f )1, it is called Phase Inverter.

/ias current compensation is provided with Rcomp) !R1 Rf# resistor.

2. Derive the e&ression "or '!ose( !oo gain o" non-inverting am!i"ier. $OR% Write

short notes on non-inverting am!i"ier.

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t the signal is applied to non-inverting terminal and feedback is as shown in circuit, the

circuit amplifier without inverting the signal.t is a negative feedback s'stem since the output is

feedback to inverting terminal. 2ifferential input, " dat i*p terminal of op-amp is 3ero, so at

node 4a5 the voltage is "i. 6ow Rfand R1form a potential divider.

The gain can be ad7usted to unit' or more b' proper selection of Rfand R1. The inputresistance of non-inverting amplifier is etremel' large !Ri# as the op-amp draws negligible

current from signal sourc.

. E&!ain Vo!tage "o!!oer.

n non-inverting amplifier, if Rf) 0 and Ri) 9 , we get a modified circuit called voltage

follower. The output voltage is e:ual to input voltage, both in phase and magnitude. $ere the

output voltage follows the i*p voltage hence the name. The main use of this unit' gain circuit

lies in the fact that its input impedance is ver' high !in order of ; AT?6@

"oltage follower is used as buffer for impedance matching, i.e., to connect high

impedance source to a low impedance load.

/.Write short notes on s0mming am!i"ier $or% With the he! o" 't. Diagram sho

that O-am 'an e 0se( as $i% Inverting a((er $ii% non-inverting a((er.

6?T%@ f it is asked as 7ust summing amplifier 'ou can write an' one either inverting

or non-inverting.B

!i#. 6"%RT6C A22%R !or# 6"%RT6C &;;6C A;=(D%R@

The above circuit is a inverting adder with three input voltages !"1,"E F "G#, three input

resistors !R1, RE F RG# and feedback resistor Rf.Assuming ideal ?p-Amp, A0( ) 9 and Ri ) 9

ince input bias current is 3ero there is no voltage drop across Rcomp. $ence the non-inverting

terminal is at virtual ground. o voltage at node 4A5 is also 3ero. 6odal e:uation b' >( at 4A5

is Thus the output is an inverted, weighted sum of inputs.>onsidering R1) RE) RG) Rf ine:uation !E# we get,

"0) - !"1H "EH "G# ---------------- !A#

The output is inverted sum of the inputs. $ence the circuit is called inverting summingamplifier.

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!ii# 6?6 I 6"%RT6C A22%R !or# &;;6C A;=(D%R@

A summer or adder that produces non-inverted sum is called non-inverting summing amplifier.

(et the voltage at node at be "A.$ence voltage at inverting terminal is also "A. since "d ) 0.The

nodal e:uation b' >( at 4A5 given, as, The ?p-amp and two resistors Rfand R form a non-

inverting amplifier, with which shows output is a non-weighted sum of inputs.

(et R1 ) R1 ) RE ) RG ) R ) Rf *E , then e:uation !A# becomes

3. Write short notes on S0tra'tor $or% Di""eren'e am!i"ier.

A basic differential amplifier can be used as a ubtractor b' considering Rf) R1)R. >onsider

all the resistor values as e:ual value then the o*p voltage can be derived using superpositionprinciples.The output "01due to input voltage "1above is found b' making "E) 0. 6ow the

circuit becomes a non-inverting amplifier having input voltage " 1*E at positive terminal and

output become, imilarl' output "0Edue to "Ealone !"1is grounded # can be given b' an

inverting amplifier

"0E ) - "E

4. Write short notes on V-I 'onverter. $or% 5)ri! 266/7

Thus the load current is proportional to input voltage and the circuit acts as a voltage to current

converter. f the load is a capacitor, it charges and discharges at a constant rate. uch convertersare used to generate awtooth or triangular waveforms.The proportionalit' constant is generall'

1*R1. $ence the circuit is called Transconductance amplifier.

t is also called voltage controlled current source. !">>#.The load current, ( ) "i*R1is same

for all t'pes of loads.(oad can be linear !e.g Resistor#, or non-linear !e.g (%2# or it can havetime dependent.6o matter what the load is, the ?p-amp will draw the current iwhose

magnitude depends onl' "i and R.Dor this ciruit, Rf) R1 ) R, $ence the load current depends

on input voltage "iand resistor R.

8. E&!ain the oeration o" an Instr0mentation am!i"ier.5)r. 2669 26637 $or% Dra a

s:stem hose gain 'an e a(;0ste( : a varia!e resistan'e an( e&!ain in (etai!.

nstrumentation amplifier is a circuit which amplifies the low level output signal of a transducer

to drive the indicator or a displa' s'stem. The above circuit is a basic instrumentation amplifier.The output voltage, "0is given b' The source "1sees an i*p impedance of RGHRJ!101k

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K &sed in numerous industrial and process control applications like precise measurement and

control of temperature, pressure, humidit', light intensit' water flow etc.,

1# decreases with increase in fre:uenc', thereb' making the

circuit sensitive to high fre:uenc' noise.

Also, at high fre:uencies, the ckt. becomes unstable and enters into oscillation.

)PP*IC)TIONS,

L n wavaeshaping circuits todetecthigh fre:uenc' components in input signal.

L As Rate of change detector in D; ;odualtor.

16. E&!ain the oeration o" an Integrator 'ir'0it $or% Write short notes onintegrator.

A circuit in which the output voltage wave is the integral of the input voltage waveform

is the Integratoror Integration )m!i"ier. where, > is the integration constant. Thusthe output voltage is directl' proportional to negative integral of input voltage and

inversel' proportional to time constant R1>D. n ?p-amp integrator the effective input

capacitance b' ;illers theorem is >f !1-Av#.

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(imited bandwidth.

)PP*IC)TIONS,

Analog computers, A2>5s

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