Anna University (Syllabus) V Semester (EEE) LINEAR ...

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Oct 7, 2013 (4 years and 2 months ago)

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Anna University (Syllabus)

V Semester (EEE)

L
INEAR INTEGRATED CIRCUITS

Two marks








U
NIT
I
I


1. Mention any four characteristics of
an
ideal operational amplifier.


C
haracteristics of
an
ideal operational amplifier
:



1.

Open loop volta
ge gain
A
OL


= ∞

(infinity)





2.

Input impedance


R
i



=


(infinity)



3.

Output impedance

R
o



=
0

(zero)



4.

Ze
ro offset


V
o

= 0 (zero)



5.

Band width

BW

=


(infinity)


2. Define

slew r
ate.


Slew rate is defined as the maximum rate of change of output voltage caused by a
step input voltage

and is usually specified in V/µ
s.

Slew rate of 741

IC is 0.5V/µS.


3. In

what way is

IC
741
S better than
IC
741?



IC741S

is

m
ilit
ary grade of amplifier and

has higher slew rate
and lower
temperature than

IC741.


4. State

the important features of instrumentation amplifier.


I
mportant features of instrumentation amplifier
:




1.

High gain accuracy



2.

High CMRR




3.

Hig
h gain stability w
ith low temperature coeffic
ient



4.


Low dc offset



5.

Low

output impedance


5. Define

CMRR.


C
ommon
M
ode
R
ejection
R
atio (
CMRR) is defined as the ratio
of

difference
mode gain
to

common mode
gain. Its

ideal value is infinity, and it i
s given by,



CMRR = | A
d
| / |A
c
|.



Where A
d

is difference mode gain and




A
c

is common mode gain.


6. Define

PSRR.


Power Supply Rejection
Ratio (
PSRR
)

is defined as the change in op
-
a
mp’s

input
offset voltage due to variations in supply
voltage. It is
expressed in microvolt per volt or
in db.



7
.

Define Tail

current.


T
ail current is defined as t
he current which is flowing through the common
emitter
resistor of the differential amplifier
.




8
.

Draw
and explain
the internal block diagram of typical op
-
amp circuit.


The internal block diagram of typica
l op
-
amp circuit is given below:


1.
Differential amplifier
s are used to provide high gain

2.

The buffer is usually an emitter follower whos
e input impedance is very high.
It

p
rev
ents loading of high gain stage


3.

The output driver is usually provided to
give

low

output impedance



9
.

List

the basic
types of
differ
ential amplifier configurations.


F
our basic
types of
differential amplifier configurations:



1
. D
ual inp
ut and
balan
ced

output



2
.
Dual input and unbalanced

output



3
.
Single input and balanced

output



4
. Single input and unbalanced output


10
.
Mention
the drawbacks of using large R
C

in differential amplifiers.


M
ain

drawbacks
:




1. A

large value of resist
ance requi
res a large chip area



2.
For

large
R
C
quiescent

drop, a large power supply will be required to



maintain a gi
ven quiescent collector current



11.

Mention

the
DC
characteristics of an op
-
amp.

DC

c
haracteristics of op
-
amp:



1
. Input bias current



2
.

Input offset current



3
.

Input offset voltage



4
.

Thermal drift


12. Why do we use R
comp

resistor?


In a bipolar op
-
amp circuit, even when the input is zero, the output will not be
zero. This is due

to the effect of bias current. This effect can be compensated using R
comp

resistor and it is given by



R
comp

= (R
i
R
f)

/ (R
i

+ R
f
) .


Where R
i

is input resistance and
R
f

is feed back resistance.


1
3
.
Define
i
nput offset voltage.

Differential
amplifier


Differential
amplifier

Buffer and
level
transulator

Output
Driver

V
o



Input offset

voltage

is

defined as the voltage

required to be applied at the input
terminals for making output voltage to zero
.


1
4
.
Define
t
hermal drift.



The
rmal drift is defined as the

change in offset current and offset voltage due to
temperatur
e.

15. List out the ac charac
teristics of an op
-
amp.


AC characteristics of an op
-
amp:



1. Frequency response

2. Slew rate


16. Define magnitude plot and phase angle plot.

Magnitude plot is defined as the one in which gain of an op
-
amp changes with
respect to the change in frequenc
y.


Phase angle plot is defined as the one in which phase angle changes with respect
to the change in frequency.


17. Define compensating network.


The compensating network is formed by components such as resistor and
capacitor for obtaining large bandwidt
h and lower closer loop gain.


18. Mention the two types of external compensation techniques.


Two types of external compensation techniques:

1.

Dominant
-
pole compensation

2.

Pole
-
zero (lag) compensation


19. Define full power response.


Full power response i
s defined as the maximum frequency of a large amplitude
sine wave with which op
-
amp can have undistorted output.


20. Define input resistance.


Input resistance is defined as the difference input resistance as seen at either of the
input terminals with the

other terminal connected to ground. For 741 IC, the input
resistance value is 2MΩ.


21. Define input capacitance.


Input capacitance is defined as the equivalent capacitance that can be measured at
either of the input terminals with the other terminal co
nnected to ground. A typical value
of C
i

is 1.4pF.


22. Define large signal voltage gain. Why it is referred so?


Large signal Voltage gain is defined as the ratio of the output voltage to
differential input voltage. Since the amplitude of the output signa
l is much larger than the
input signal, the voltage gain is commonly referred to as large signal voltage gain.


23. What does the output voltage swing indicate?



The output voltage swing indicates that the value of positive and negative voltage
of an op
-
a
mp and it should never exceed the supply voltage V
+
and V
-

.


24. Define output resistance.


Output resistance R
o

is defined as the resistance measured between the output
terminal of the op
-
amp and ground. The typical value is 75Ω for 741 ICs.

25. List out

the different types of op
-
amp.


Different types of op
-
amp:



1. Bipolar op
-
amp



2. FET op
-
amp



3. MOSFET op
-
amp



26. Define input offset voltage.


Input offset voltage is defined as the voltage that must be applied between the
input terminals of an o
p
-
amp to nullify the output. For IC 741, the maximum value is

6 mV.


27. Define input offset current.


Input offset current is defined as the algebraic difference between the currents into
the (
-
) input and (+) input. For 741 IC the maximum value is 200
nA.


28. Define input voltage range.


Input voltage range is defined as the common
-
mode voltage that can be applied to
both input terminals without disturbing the performance of an op
-
amp. The range of the
input common
-
mode voltage is
+

13 V, for 741 IC.


29. Define output short circuit current.


Output short circuit current is defined as the current that may flow if an op
-
amp
gets shorted accidentally and is generated high. The op
-
amp must be provided with short
circuit protection. The short circuit curren
t I
SC

for 741C is 25 mA.


30. Define supply current.


Supply current I
S
is defined as the current drawn by the op
-
amp from the power
supply. It is 2.8 mA for 741 IC.








UNIT III




Analog multiplier and PLL



1.

What is an analog multiplier?

An a
nalog multiplier is the one which produces an output voltage (V
o
)
proportional to the product of two input voltages V
X
and V
Y
. The output voltage is given
by,

V
o

= K V
X

V
Y
.

Where K is a scale factor, usually its value is 1/ (10)V
-
1
.


2.

What is a four
quadrant multiplier?


A multiplier that accepts inputs of either polarity and preserves the correct
polarity relationship at the output is referred to as a four quadrant multiplier.


3.

Give the applications of analog multipliers.


Applications of analog mult
ipliers:



1. Frequency doubling



2. Frequency shifting



3. Phase angle detection



4. Real power computation



5. Multiplying two signal, dividing and squaring of signals


4.

What is the unique feature of Operational Transconductance Amplifier (OTA)?



The

unique feature of OTA is that, it is possible to vary g
m

(transconductance)
over a wide range, by means of an external control current and OTA is an inherently
fast device.



5.

Give the typical applications of Operational Transconductance Amplifier( OTA)



Applications of Operational Transconductance Amplifier

(
OTA):

1.

To implement programmable amplifiers and integrators in

audio processing and electronic music synthesis

2.

As current switches in sample and hold applications

3.

Using VLSI techniques in
neural networks


6.

List the basic limitations of Operational Transconductance Amplifier (OTA).


The basic limitations of Operational Transconductance Amplifier:

1.

Output current is non linear when the input voltage exceeds 20mV

2.

As the control current I
C

is var
ied to adjust gain or resistance,

offset voltage, input bias current and slew rate are also affected

3.

Temperature affects the performance of OTA


7.

Draw the general block diagram of phase locked loop.

Where V
s
and f
s

are the signal voltage and signal freque
ncy respectively,

V
c
and f
c

are the control voltage and frequency of the control signal respectively,

V
e

is the error voltage

V
o

is the output voltage.



8.

Define lock in range.



Lock
-
in renge is defined as the range of frequencies over which
the PLL can
maintain lock with the incoming signal. It is also called as tracking range. The lock
-

in range is expressed as a percentage of VCO frequency f
o.


9.

Define capture range.



Capture range is defined as the range of frequencies over which the PLL c
an
acquire lock with an input signal. This parameter is expressed as a percentage of
VCO frequency fo.


10.

Define Pull
-
in time.

Pull
-
in time is defined as the total time taken by the PLL to establish lock. This
depends on the initial phase and frequency diffe
rence between the two signals as well as
on the overall loop gain and loop filter characteristics.


11.
What is the basic function of phase detector?


The basic function of the phase detector is, to compare the phase and frequency of
the incoming signal wi
th the output of VCO in PLL. If the two signals differ in frequency
and/or phase, an error signal is generated, it is basically a multiplier.


12.
What are the two types of phase detectors available?



Two types of phase detectors:

1.

Analog phase detector

2.

D
igital phase detector

13. The first stage in a PLL is

phase detector

followed by

low pass filter
.


14. List out some examples of digital phase detectors.


Examples of digital phase detectors:

1.

Exclusive OR phase detector

2.

Edge
-

triggered phase detector

3.

Mon
olithic phase detector



]
15. What is voltage controlled oscillator?


The voltage controlled oscillator is defined as the one in which the frequency of
the output signal (V
o
) is controlled by the control voltage (V
c
).


16. What is the function of VCO in PL
L?


The error voltage in phase detector is amplified and applied as a control voltage
(V
c
) to VCO. The signal V
c

Shifts the VCO frequency in a direction to reduce the
frequency difference between f
s

and f
o .

Once the action starts, we say that the signal
is in
the capture range. The VCO continues to change frequency, till its output frequency is
exactly the same as the input signal frequency.


17. List out the typical applications of Phase Locked Loop.


Applications of Phase Locked Loop:

1. Frequency

multiplication/division

2. Frequency translation

3. AM detection

4.

FM demodulation and

5.

FSK demodulation.


18. How can FM signal demodulated using PLL?


If PLL is locked to a FM signal, the VCO tracks the instantaneous frequency of
the input signal. The
filtered error voltage which controls VCO and maintains lock with
the input signal is the demodulated FM output. The VCO transfer characteristics
determine the linearity of the demodulated output.


19. What is frequency shift keying technique?


Frequency S
hift Keying (FSK) technique is a type of the data transmission in
which, binary data is transmitted by means of a carrier frequency which is shifted
between two preset frequencies.

20. What is frequency shift?


The difference between the two preset input
frequencies of Frequency Shift
Keying (FSK) demodulator is called frequency shift.


21. What is frequency shift keying demodulation?


The binary data which is shifted by a carrier frequency between two preset
frequencies are retrieved by using Frequency Sh
ift Keying ( FSK) demodulator.


22. What will be the output frequency if a Phase Locked Loop (PLL) frequency


translator has a center frequency of ‘f’ and input frequency of ’f
1
’?


The output frequency is f+f
1
.


23. What are the main advant
ages of using low pass filter in PLL circuits?


Main advantages of using low pass filter:

1.

The low pass filter used in PLL not only removes the high frequency
components and noise, but also controls the dynamic characteristics of
PLL.

2.

The charge on the filt
er capacitor gives a short time memory to the
PLL. Thus, even if the signal becomes less than the noise for a few

cycles, the dc voltage on the capacitor continues to shift the frequency
of the VCO till it picks up the signal again.


24. Why is the captu
re range of PLL dependant upon low pass filter (LPF)


characteristics?

The capture range of PLL depends on low pass filter characteristics because it
removes the high frequency components and noise ,as the bandwidth reduces the
capture range of PL
L is also get reduced.







UNIT II




Applications of Operational Amplifiers



1. List out the important features of an instrumentation amplifier.


Important features of an instrumentation amplifier:


1. High gain accuracy


2. High CMRR


3. High gain sta
bility with low temperature coefficient


4. Low dc offset

5. Low output impedance


2. Mention the disadvantages of passive filters.


Disadvantages of passive filter:

1. Inductors become large, heavy and expensive for low frequency


applications.

2. Mor
e number of turns of wire must be used which in turn adds to the


series resistance degrading inductor’s performance.(i.e.)low Q,


resulting in high power dissipation.


3. What is an inverting amplifier?


Inverting amplifier is the one in which a
signal is applied to the inverting input
terminal. The output voltage is fedback to the inverting input terminal through feedback
resistance (R
f
)


input resistance (R
i
) network. The output signal is the amplified form of
input signal with a phase shift of

180
0

.The circuit diagram of inverting op
-
amp is given
below:


4. What is a non inverting amplifier?


Non inverting amplifier is the one in which a signal is applied to the non inverting
input terminal and the output is feedback to the inverting input ter
minal, the circuit
amplifies without inverting the i/p signal. The circuit diagram of non
-
inverting amplifier
is given below:


5. What is linear op
-
amp circuit?


An op
-
amp circuit which has the output signal with the same shape as that of the
input signal
is called linear op
-
amp circuit. The op
-
amp does not go to saturation during
its cycle.


6. List out some of the linear op
-
amp circuits.


Linear op
-
amp circuits:

1. Inverting amplifiers

2 .Non inverting amplifiers

3. Differential amplifiers

4. Instrumenta
tion amplifiers

5. Current boosters etc.


7. What is non linear op
-
amp circuit?


An op
-
amp circuit which has the output signal with a different shape from the
input signal is called non linear op
-
amp circuit. The op
-
amp saturates during part of its
input c
ycle.


8. List out some non linear op
-
amp circuits.


Non linear op
-
amp circuits:

1.

Comparators

2.

Wave shapers

3.

Active diode circuits.


9. How is the gain stabilized by negative feedback?


Negative feedback is used mainly to stabilize the overall voltage gain. I
f the open
loop voltage gain A
OL

increases for any reason, the output voltage will increase and feeds
back more voltage to the inverting input. This opposing feedback voltage reduces
inverting input voltage V
2
. Therefore even though A
OL
has increased, inve
rting input
voltage V
2

has decreased and the final output increases much less that it would be
without the negative feedback.


10. What is voltage follower?


Voltage follower is the circuit in which the output voltage follows the input
voltage both in magn
itude as well as in phase. The circuit diagram of voltage follower is
given below:


11. Mention the main applications of differentiator.

Main applications of differentiator:

1.

used in wave shaping circuits to detect high frequency components
in an input sign
al.

2.

used as rate of change detector in FM modulations.



12. List the drawbacks of ideal integrator.

Drawbacks of ideal integrator:



1. At low frequencies (dc), gain becomes infinity.



2. When the op
-
amp saturates, ideal integrator behaves like an open



circuit.


13. What is a differentiator?


A differentiator is the circuit which perform the mathematical operation of
differentiation, i.e., the output waveform is the derivative of the input waveform. The
output voltage
is given by



V
o
=
-

R
f
C
1
dv
i
/dt



Where R
f

is the feedback resistor,

C
1
is the input capacitance and




v
i

is the input voltage.


14. Mention the main applications of differentiator.


Main applications of differentiator:

1.

used in wave shaping circuit
s to detect high frequency components in an
input signal.

2.

used as rate of change detector in FM modulations.



15. List the drawbacks of ideal integrator.


Drawbacks of ideal integrator:



1. At low frequencies (dc), gain becomes infinity.



2. When the op
-
amp saturates, ideal integrator behaves like an open


circuit.


16. Why is the practical integrator called as lossy integrator?


The gain of the integrator at lower frequencies can be limited to avoid the
saturation pro
blem, if the feedback capacitor C
f

is shunted by a resistor R
f
.The parallel
combination of R
f

and C
f

behaves like practical capacitor, which dissipates power,
unlike an ideal capacitor. For this reason, the circuit is called as lossy integrator.


17.
Mention the two types of voltage to current converter?


Two types of voltage to current converter:

1.

V
-
I converter with floating load

2.

V
-
I converter with grounded load


18. Give the applications of V
-
I converter.

Main applications of voltage to current conve
rter:

1.

Low voltage dc and ac voltmeter

2.

In LED and Zener diode tester


19. Write the major function of instrumentation amplifier.


The major function of instrumentation amplifier is to amplify the low level output
signal so that it can drive the i
nductor or display.


20. What is an oscillator?


An oscillator is basically a positive feedback circuit where, a fraction of the
output voltage V
o

is fedback to the input end of the basic amplifier, which is in phase
with the signal to the basic amplifier.



21. Mention the conditions to be satisfied for sustained oscillation.


Conditions to be satisfied for sustained oscillation:

1. The magnitude of product of the gain of the basic amplifier(A
v
) and

the gain of the feedback amplifier(
β) should be equal to 1 ; |A
v
β| = 1.


2. Āngle between gain of the basic amplifier(A
v
)

and gain of the feedback


amplifier(β) should be equal to 0
0
or 360
0

.



22. Classify sine
-
wave oscillators based on the range of frequency.


Sine
-
wave oscill
ators can be classified according to the range of frequency as

1.

RC Oscillators for audio frequency

2.

LC Oscillators for radio frequency


23. Define Electric filter.


An electric filter is defined as afrequency selective circuit that passes a specific
band o
f frequencies and blocks or attenuates signals of frequencies outside this band.


24. Mention the classification of electric filters.


Classifications of electric filters:

1. Analog or digital

2. Passive or active

3.

Audio (AF) or radio frequency (RF).


25.
Mention the advantages of active filters.


Advantages of active filter:




1. Gain and frequency adjustment is flexible

2. No loading problem

3. Cost is low


26. Define frequency scaling.


Frequency scaling is defined as the procedure used to convert

an Original cut
-
off
frequency f
h

to a new cut
-
off frequency f
h
.



27. What is a comparator?


A comparator is a circuit which compares a signal voltage applied to one input of
an op
-
amp with known reference voltage at other input. It is basically an op
-
am
p with
output
+

(V
sat
).


28. List out the applications of comparator.


Applications of comparator:

1.

Zero crossing detector

2.

Window detector

3.

Time marker generator

4.

Phase meter


29. What is Schmitt trigger?


Schmitt trigger is an inverting comparator with pos
itive feedback. It converts an
irregular
-
shaped waveform to a square wave or pulse, and is called as squaring circuit.



UNIT


IV

A
nalog to digital and digital to analog converters


1. What is the use of sample and hold circuit?


A sample and hold circuit

samples an input signal and holds onto its last sampled
value, until the input is sampled again.


2. Mention few applications of sample and hold circuit.


Applications of sample and hold circuits :

1. Analog to digital systems

2. Pulse code modulation sy
stems.


3. What is sample period?


The time period during which the voltage across the capacitor is equal to input
voltage is called sample period.


4. What is hold period?


The time period during which the voltage across the capacitor is held constant is
called hold period.


5. List out various resistive DAC techniques available.


Various resistive DAC techniques available:

1.

Weighted resistor DAC

2.

R
-
2R ladder

3.

Inverter R
-
2R ladder


6. What is the resolution for a DAC?


The resolution of the analog to digital

converter is the smallest change in voltage,
which may be produced at the output (or input) of the converter.


7. List out direct type ADCs.


Direct type ADCs:

1.

Flash (comparator) type converter

2.

Counter type converter

3.

Tracking or servo converter

4.

Successive

approximate type converter


8. List out some integrating type converters.


Most widely used integrating type converters:

1.

Charge balancing ADC

2.

Dual slope ADC


9. What is integrating type converter?


An ADC Performs conversion in an indirect manner by firs
t changing the analog
input signal to a linear function of time or frequency and then to a digital code is known
as integrating type converter.



10. Where are the successi
ve approximation type ADCs used?


The successive approximation ADCs are used in applications such as, data
loggers and instrumentation where conversion speed is important.


11. The input stage of any data acquisition system will be

sample and hold circuit
.


12. Name the various types of electronic switches used in DAC.


Various types of electronic switches used in DAC:

1.

Single pole double throw switch

2.

Totem pole MOSFET switch

3.

CMOS inverter switch


13. Mention the main disadvantage of flash type ADC?


The ma
in disadvantage of flash type A/D converter is that, the number of
comparators required almost doubles for each added bit.

For example: A 2
-
bit ADC Requires 3 comparators, 3
-
bit ADC requires 7 comparators.


14. How many total number of clock pulses require
d for 8
-
bit successive
-
approximation type A/D converter?


The total number of clock pulses required for 8
-
bit successive
-
approximation A/D
converter is 8.


15. Mention the main advantages of integrating type ADCs?


Main advantages of integrating type ADCs:

1.

The integrating type of ADCs do not require a S/H circuit at the input

2.


It is possible to transmit frequency even in noisy environment


16. Define absolute accuracy.


Absolute accuracy is the maximum deviation between the actual converter output
and ide
al converter output.


17. Define relative accuracy.


Relative accuracy is the maximum deviation between the actual converter output
and ideal converter output after gain and offset errors have been removed.


18. Draw the block diagram of successive
-
approxi
mation type ADC.



19. What is monotonic DAC?


A monotonic DAC is the one whose analog output increases for an increase in
digital input.


20. What is settling time?


Settling time is the time taken for the output to settle within a specified band
+
(
1/2)
LSB of its final value following a code change at the input. It ranges from 100 ns to
10
μs depending on word length and type of circuit used.


21. Write the main logic involved in Delta modulation.


Delta modulation (DM) is the single bit version of PCM. In this modulation the
difference between original sample and previous sample of error si
gnal is encoded into a
single bit. If the current sample is smaller than the previous sample, logic 0 is transmitted.
If the current sample is larger than the previous sample, logic 1 is transmitted.


22. Mention the main function of comparator in delta m
odulation transmitter.


The comparator compares the pulse analog signal and the previous signal and
gives output as logic 1(+V) or logic 0(
-
V).


23. Write the two problems associated with DM.


Problems associated with DM:

1.

Slope overload

2.

Granular noise


24
. Where are analog switches used?


Analog switches are used in chopper amplifiers, D/A converters, function
generators, S/M amplifiers and switching power supplies.


25. What is slope overload?


When the analog input signal changes at a faster rate than DA
C can maintain, the
analog signal is greater than the delta modular can maintain, and this is called as the slope
overload.


26. What is granular noise?


When the original analog input signal has a relatively constant amplitude, the
reconstructed signal h
as variations that were not present in the original signal. This is
called as granular noise.


27. What is adaptive delta modulation?


Adaptive delta modulation is a delta modulation system where the step size of the
DAC is automatically varied depending o
n the amplitude characteristics of analog input
signal.







UNIT V





SPECIAL FUNCTION ICs


1.

Write the main function of 555 Timer.

The 555 Timer is a highly stable device for generating accurate time delay
or oscillation.


2.

Mention the applications of 55
5 Timer.



The applications of 555 Timer are:

It can be used as

1.

An Oscillator,

2.


Pulse generator,

3.

Ramp and square wave generator,

4.

Monoshot multivibrator,

5.

Burglar alarm,

6.

Traffic light control and

7.

Voltage monitor.



3.

The other name for monostable multivibr
ator is
one shot multivibrator
.


4. Mention the applications of the monostable mode of operation of 555 IC.



The applications of the monostable mode of operation of 555 IC are:

1.

Missing pulse detector,

2.

Linear ramp generator,

3.

Frequency divider and

4.

In pulse
width modulation.


5.
Mention the main applications of missing pulse detector monostable circuit
.



The main applications of missing pulse detector monostable circuit are:

1.

It is used to detect missing heart beat and

2.

It is used for speed control and me
asurement.




6. Write the main function of voltage regulator.



The main function of voltage regulator is to provide a stable DC voltage


for processing other electronic circuits.



7. List the different types of voltage regulators
.



T
he different types of voltage regulators are:

1.

Fixed output voltage regulator (positive or negative),

2.

Adjustable output voltage regulators (positive or negative),

3.

Switching regulators and

4.

Special regulators.



8. What is a voltage regulator?



A voltag
e regulator is an electronic circuit that provides a stable dc voltage

independent of the load current, independent of the load current, temperature
and
ac line voltage variations.

9.

What are the four main parts of voltage regulators?



The four main p
arts of the voltage regulators are:

1.

Reference voltage circuit,

2.

Error amplifier,

3.

Series poles transistor and

4.

Feed back network.


10. Define Load regulation.

Load regulation is defined as the change in output voltage for a change in
input current. It is usu
ally expressed in millivolts or as a percentage of V
o

.


11. List the main advantages of voltage regulators
.



The main advantages of voltage regulators are:

1.

Short circuit protection and

2.

Output voltage (positive or negative) can be varied.


12. List the l
imitations of IC
-
723 regulators.



The limitations of IC
-
723 regulators are:

1.

No in
-
built thermal protection and

2. No short circuit current limits.


13. List the drawbacks of series regulators.


The draw backs of series regulators are:


1. The input

step down transformer used is bulky and most expensive


component.

2.

Since it operates at low line frequency, large values of filter capacitors


are required.

3.

Efficiency is less and

4.

More power is dissipated in the series pass transisto
r, which is always in


the active region.



14. What is switched capacitor filter?

A switched capacitor filter is a three terminal device, which consists of
capacitors, periodic switches and operational amplifier whose open circuit vo
ltage
transfer characteristics represents filtering characteristics.


15. Why are series regulators called as linear regulators?

Since the transistors conduct in the active or linear region, these regulators
are called as linear regulators.


16. Define ri
pple rejection.

Ripple rejection is a measure of a regulator’s ability to reject ripple
voltage. It is expressed in db.



17. Write the uses of voltage regulators.

Voltage regulators are commonly used for on
-
card regulation and
laboratory type power switch
es. Switch type regulators are used as control circuits
in pulse width modulation, Push Pull Bridge and series type switch mode
supplies.


18. Where are switched capacitor filter used?


Switched capacitor filter are used in:

1.

Low pass filter,

2.

High pass filter,

3.

Band pass filter and

4.

Band reject filter.


19. What is frequency to voltage converters?

A converter which generates an output voltage that is linearly proportional
to the input frequency waveform is frequency to voltage converter.


20. De
fine Modulation.


The process of raising the audio signal to RF frequencies is called as modulation.


21. Define resonance.

At a particular frequency when the inductive reactance X
L

equals the
capacitor reactance X
C
, Then the circuit behaves as a purely r
esistive circuit. This
phenomenon is called as resonance.



22. Where does the thermal noise occur? What is the cause?



Thermal noise occurs in all passive resistors including the stray series
resistances of practical inductors and capacitors. Thermal noi
se is due to the random
thermal motion of electrons.



23. Define optocoupler.



A combination of LED and photodiode is called as an optocoupler. This
device can couple the input signal to the output circuit.



24. Mention the main advantages of optoco
upler.




The key advantage of an optocoupler


is the electrical isolation between
the input output circuits. With an optocoupler, the only contact between the input
and output is a beam of light. Because of this, it is possible to have an insulation
resis
tance between the two circuits in the thousands of mega ohms.



25. List the advantages of using optic fibres.



The advantages of using optic fibres are:



1. Creator information capacity,



2. Immunity to cross talk,



3. Immunity to static interferen
ces,



4. Environmental immunity,



5. Safety and



6. Security and longer lasting.



26. Define Line regulation
.

Line regulation is defined as the percentage change in the output voltage
for a change in the input voltage. It is usually expressed in milliv
olts.