EC6404 Linear Integrated Circuits

Department of ECE

2016-2017

UNIT I : BASICS OF OPERATIONAL AMPLIFIERS

PART A
1. List the advantages of IC over discrete component circuit. (Nov 2013)
Low cost, Small size, High reliability, Improved performance.
2. What is the purpose of a current source in integrated circuits? (Nov 2012)
By improving the CMRR of differential amplifier, its performance can be improved. To improve CMRR,
common mode gain Ac must be reduced as much as possible. When this happens RE will be tending to infinity.
But there are practical limitations in selecting the magnitude of an enormous value of resistance. Use of a
constant current bias instead of RE is the practical solution for this problem. Without physically increasing the
value of RE, the transistor operated at a constant current gives the effect of very high value of resistance. This is
the importance of a current source in an IC.
4. In what type of applications Widlar current source is used.
Widlar current source is used in OP-AMPs which require low input current of the order of 5A..
5. What is an op - amp? List its functions.
The Op amp is a versatile IC which is capable of performing various applications and operations like amplifier,
summer, differentiator, Integrators, Etc
6. What is an op-amp? List its functions.
The op-amp is a multi terminal device, which internally is quite complex. It is a direct-coupled high gain
amplifier consisting of one or more differential amplifiers, followed by a level translator and an output stage.
Function: Op-amp amplifies the difference between two input signals.
7. List the ideal characteristics of an op-amp. (or)
List the characteristics of ideal Op-amp and draw its equivalent circuits? (Nov 2014)
The ideal characteristics of an op-amp are as follows:

Open loop voltage gain, AOL =

Infinite Input impedance, Ri =

Zero Output impedance, RO = 0

Infinite Bandwidth,
BW =

Zero offset voltage, i.e. VO = 0 when V1 = V2 = 0;

8. List the essential terminals of an op-amp.
Op-amp has five basic terminals, that is, two input terminals, one output terminal and two power supply
terminals. Inverting input terminal : Pin 2,Non- inverting input terminal : Pin 3,Output terminal : Pin 6 and
Power supply terminals : Pin 4& 7
9. Explain the virtual ground concept with a suitable example.
We know that Vd = Va - Vb = 0; Node B is grounded. Therefore Vb = 0; But Vd = 0; Va = Vb ;
Node A is at virtual ground. ie since node B is at ground node A is also at ground imaginarily.
10. What are the factors that affect the stability of an op-amp?
The factors that affect the stability of an op-amp are closed loop gain and phase shift.
11. What are the various methods available for frequency compensation?
There are two types of compensating techniques used for frequency compensation. They are namely External
compensation and Internal compensation. External frequency has two methods for compensation namely
Dominant pole compensation and Pole-zero compensation
12. An operational amplifier has a slew rate of 4V/s. Determine the maximum frequency of operation to
produce a distortion less output swing of 12V. (Nov 2014)
Slew rate (SR) =2fVp / 106 V/s, Vp- Maximum amplitude of the output.
Given: SR = 4 V/s, Vp= 12V
f = SR106 / (212) = 53.078kHz
13. Mention some applications of op-amp in open loop mode.
Some of the applications of op-amp in open loop mode are as follows:
Comparator, Zero crossing detector, Window detector, Time marker generator, Phase meter
14. Define input offset current and input offset voltage. (Nov 2013)
INPUT OFFSET CURRENT: The algebraic difference between the currents into the (-) input and (+)input is
referred to as input offset current .It is 200Na maximum for 741C.
INPUT OFFSET VOLTAGE: Ideally, for an Op-amp when no input is applied output voltage must be zero.
However, some output voltage is present though input is not applied. Thus, offset voltage is the voltage that
must be applied between the input terminals of an op-amp to nullify the output.
Since this voltage could be positive or negative its absolute value is listed on the data sheet. For 741C,
maximum value is 6mV.
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EC6404 Linear Integrated Circuits

Department of ECE

2016-2017

15.Design a circuit using op-amp whose gain is 3.

The op-amp inverting amplifier is shown.

Gain

Rf
V0

3
Vi
R1

Let R1 1k
R f 3 R1 3k

16. What is meant by negative feedback?

The feedback circuit connected across the inverting input& the output terminal is called negative feedback.
17. Why are FET op-amps better than BJT op-amps? Op-amps using FETs in the input stage offer some
very significant advantages over bipolar op-amps, especially in areas as input impedance, input bias and
offset currents and slewing rate as shown in table
Op-amps using FETs in the input stage offer significant advantages over bipolar op-amps especially in areas as
input impedance, input bias and offset currents and slew rate as shown in table:
Parameter
BJT
JFET
MOSFET
Input resistance

Input gate current

109
1 nA

1012
1 pA

Input offset current

20 nA
2 pA
0.5 pA
Slewing rate
1 V/s 3 V/s 10 V/s
18. Define input bias current and input offset current of an operational amplifier. (Nov 2015)
Input Bias current: The average of currents entering into the (-) input terminal & (+) input terminal of an opamp is called input bias current. Its value is 500nA for 741C.
INPUT OFFSET CURRENT: The algebraic difference between the currents into the (-) input and (+)input is
referred to as input offset current .It is 200Na maximum for 741C.
19. Define slew rate. Mention it ideal value expected in an op-amp. (May 2014)
Slew rate is defined as the maximum rate of change of output voltage caused by a step input voltage and is
usually specified is V/s. An ideal slew rate is infinite which means that op-amps output voltage should
change instantaneously in response to input voltage.
20. Define CMRR AND PSRR. Mention their ideal values. (May 2013)
CMRR: The relative sensitivity of an op-amp to a difference signal as compared to a common mode signal is
called common mode rejection ratio and gives the figure of merit for the differential amplifier.
|A |
d where Ad = Differential mode gain, Ac = common mode gain, CMRR is typically infinite.
| Ac |
PSRR: The change in an op-amps input offset voltage due to variations in supply voltage is called supply
voltage rejection ratio. It is also termed as power supply rejection ratio or power supply sensitivity. For 741C,
SVRR=150V/V.
21. Explain thermal drift related to an op-amp.
Bias current, offset current and offset voltage change with temperature. A circuit carefully nulled at
250C may not remain so when the temperature rises to 35 0C.This is called thermal drift. Often current drift is
expressed in nA/0C and offset voltage drift in mV/0C.
22. What is the maximum undistorted amplitude, that a sine wave input of 10 kHz, can produce, at the
output of an op-amp whose slew rate is 0.5 V/s? (Nov 2012)
Slew rate (SR)= 2fVp / 106 V/s, Vp- Maximum amplitude of the output
Given: SR= 0.5 V/s, f= 10kHz
Vp=SR106 / (210k)=1.99 V
23. State the limitations of discrete circuits. (May 2013)
High cost, Large size, Low reliability, Reduced performance.
24. A differential amplifier has a differential voltage gain of 2000 and a common mode gain of 0.2.
Determine the CMRR in dB. (May 2015)
CMRR = 20 log |Ad/Ac|
Ad = 2000, Ac=0.2. (Given)
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2016-2017

CMRR = 2000 / 0.2 = 10000

CMRR in dB = 20 log |Ad/Ac| = 20 log 10000 = 20* 4 = 80dB.
25. Define Slew rate and what causes the slew rate? (May 2015)
In electronics, slew rate is defined as the maximum rate of change of output voltage per unit of time and is
expressed as volts per second. Limitations in slew rate capability can give rise to non-linear effects in electronic
amplifiers.
26. Mention two advantages of active load over passive load in an operational amplifier.(Nov 2015)
The difference mode gain and CMRR is directly proportional to the R C in differential amplifier. To apply large
resistance RC to achieve high CMRR. But the use of large resistance value R C occupies large chip area and it
needs large power supply so the passive load RC is replaced by the current mirror as active load.
27. Find the maximum frequency for sine wave output voltage 10Vpp with an op-amp whose slew rate is
1V/s. (May 2016)
Vpp=10V
Slew Rate = 2fmaxVm = 1V/s
fmax = (1 x 106)/ (2 x 5)
28. Differentiate the Ideal and Practical characteristics of an op-amp. (May 2016)
S.No Ideal Characteristics
Practical Characteristics
1.
Open loop gain = .
Open loop voltage gain = several thousands.
2.
Input impedance = .
Input impedance is greater than 1M.
3.
Output impedance = 0.
Output impedance is few hundred ohms.
4.
Bandwidth = .
Bandwidth is very small.
5.
Zero Offset Vo = 0 when V1=V2=0.
Offset voltage is some non zero value.

Part B
1.(i)With a neat circuit diagram and with necessary equations, explain the concept of Widlar current source
used in op-amp circuit.
(ii)For the non-inverting op-amp shown in the figure below, find the output voltage V o. (Nov 2011, April 2011)

2. (i)With a neat block diagram, explain the general stages of an OP-AMP IC.(6)
(ii)Explain, with a circuit diagram, the working of BJT-emitter coupled differential amplifier. Also explain the
concept of active load and sketch the relevant circuit diagram.(10) (Nov 2011, Nov 2013)
3. (i) Compare different configurations of differential amplifier.(8) (May 2013)
(ii) For a dual input, balanced output differential amplifier, Rc=2.2k, RE=4.7 k, Rs1=Rs2=50.
The supply voltages are 10V. The hfe for the transistor is 50. Assume silicon transistors and hie= 1.4k.
Determine the operating point values, differential gain, common mode gain and CMRR. (8)
4. (i)Draw the circuit of basic current mirror and explain its operation. Also discuss about, how current ratio can
be improved in the basic current mirror. Sketch the improved circuit and explain. (10)
(ii)Define output off-set voltage. Explain methods to nullify off-set voltage (6) (Nov 2012)
6.(i) Explain the working of BJT differential amplifier with active load. (12)
(ii) Write down the characteristics and their respective values of an ideal operational amplifier.(4) (Nov 2013)
7. (i)List and explain the non-ideal DC characteristics of op-amp.(8)
(ii)Explain AC characteristics of op-amp. (8) (May 2012, Nov 2013, Nov 2014)
8. (i)With simple schematic of differential amplifier, explain the function of operational amplifier.
(ii) Briefly explain about constant current source. (April 2015)
9. (i) Briefly explain the techniques used for frequency compensation.
(ii) How do the open loop and the closed loop gain of an op-amp differ? (April 2015)
10. Explain the different types of resistor fabrication in an IC. (Nov 2014)
11. (i) With the schematic diagram explain the effect of Re on CMRR in differential amplifier. (4)
(ii) Discuss about the methods to improve CMRR.(12) (May 2016)
12. (i) Write a note on stability criteria and frequency compensation techniques applied in op-amp.(12)
(ii) A non-inverting amplifier with the gain of 300 having an input offset voltage of 3mV. Find the output
voltage when the input is 0.01 sin t Volt. (4) (May 2016)
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ISO9001:2008

EC6404 Linear Integrated Circuits

Department of ECE

2016-2017

13. With a neat diagram, explain the input side of the internal circuit diagram of IC 741. (Nov 2015)
14. What is a need for frequency compensation in an op-amp? With the suitable illustration, explain the polezero frequency compensation technique. (Nov 2015)

UNIT II: APPLICATIONS OF OPERATIONAL AMPLIFIERS

PART-A
1. What are the limitations of basic differentiator?
At high frequencies, a differentiator may become unstable and break into oscillation.
The input impedance (ie., 1/C1) decreases with increase in frequency, thereby making the circuit sensitive to
high frequency noise.
2. What is the limitation of basic integrator?
At low frequencies, the feedback capacitor behaves as an open circuit and there is no negative feedback. The
op-amp thus operates in open loop, resulting in an infinite gain. In practice, of course, output never becomes
infinite, rather the output of the amplifier saturates at a voltage close to the op-amp positive or negative power
supply depending on the polarity of the input dc signal.
3. What is the use of differentiator and integrator circuits?
The op-amp differentiator and integrator are useful for signal wave shaping.
4. Define a summing amplifier.
A summing amplifier is a circuit whose output is the sum of several input signals. It may be inverting summing
amplifier and non-inverting summing amplifier.
5. On what does the damping co-efficient of a filter depend.
Damping is determined by the amplifiers gain. Bessel filter is a heavily damped filter ( > 1.7). It is very
stable, but rolls-off very early in the pass band.
Butterworth filters ( = 1.414) gives maximally flat pass band. A Chebyshev filters ( < 1.4 ) provides faster
initial roll-off rate but gives poorest transient response.
6. What is an instrumentation amplifier?
In a number of industrial and consumer applications, one is required to measure and control physical quantities.
Some typical examples are measurement and control of temperature, humidity, light intensity, water flow etc.
these physical quantities are usually measured with the help of transducers. The output of transducer has to be
amplified so that it can drive the indicator or display system. This function is performed by an instrumentation
amplifier.
7. What are the features of an instrumentation amplifier?
High gain accuracy, High CMRR, High gain stability with low temperature coefficient, Low dc offset
Low output impedance. There are specially designed op-amps such as A 725 to meet the above stated
requirements of a good instrumentation amplifier.
8. What is the other name for voltage to current converter? What are the uses of V-to-I converters?
The other name for voltage to current converter is the transconductance amplifier. The V-to-I converters are
useful in low voltage dc and ac voltmeters, LED and zener diode testers.
9. What is the other name for current to voltage converter? What are the uses of I-to-V converters?
The other name for current to voltage converter is the transresistance amplifier. The I-to-V converters are used
for testing photo devices. Photocell, photodiode and photovoltaic cell give an output current that is proportional
to an incident radiant energy or light. The current through these devices can be converted to voltage by using a
current to voltage converter and thereby the amount of light or radiant energy incident on the photo device can
be measured.
10. Discuss the disadvantages of passive filters.
Passive filters work well for high frequencies, that is, radio frequencies. However, at audio frequencies,
inductors become problematic, as the inductors become large, heavy, and expensive. For low frequency
application, more number of turns of wire must be used which in turn adds to the series resistance degrading
inductors performance, ie. Low quality factor results in high power dissipation.
11. Why are active filters preferred?
Active filters are preferred over passive filters because they use op-amp as the active element, and resistors and
capacitors as the passive elements. The active filters, by enclosing a capacitor in the feedback loop, avoid using
inductors. In this way, inductor less RC active filters can be obtained. Also, as op-amp is used in non-inverting
configuration, it offers high input impedance and low output impedance. This will improve the load drive
capacity and load is isolated from the frequency-determining network. Because of the high input impedance of
the op-amp, large value of resistors can be used, thereby reducing the value (size and cost) of the capacitors
required in the design.
12. What is the roll-off rate of a first order filter?
A first order active filter consists of only one RC pair & has a roll-off rate of20dB/decade. The roll-off rate
increases with the order of the filter. An n-th order filter has a roll-off rate of 20n dB/decade.
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ISO9001:2008

EC6404 Linear Integrated Circuits

Department of ECE

2016-2017

13.What is a Sallen- Key filter?

A second order filter consists of two RC pairs and has a roll-off rate of 40 dB/decade. A general second order
filter is known as Sallen Key filter.
14. What is a comparator? List the applications of comparator. (or) Draw the circuit diagram of the
comparator. Mention its applications. (May 2016)
A comparator is a circuit, which compares a signal voltage applied at one input of an op-amp with a known
reference voltage at the other input. It is basically an open loop op-amp with analog inputs and digital output (+
or Vsat = Vcc ). Circuit Diagram:

Application: Zero crossing detector, Window detector, Time marker generator and, Phase meter.
15. What is Schmitt trigger?
Schmitt trigger is a comparator with positive feedback. In this circuit, the input voltage triggers
the output every time it exceeds certain voltage levels called upper threshold V UT and lower
threshold VLT. It converts slowly varying waveforms into square wave.
16.Draw the transfer characteristics of an ideal comparator and a practical comparator.

Practical comparator
Ideal comparator
17.What is a precision diode? How does it differ from the conventional amplifier? (Nov.2012)
A diode in the feedback loop of an op-amp behaves as a precision diode as its cut-in voltage gets divided by the
open-loop gain of op-amp. This circuit is called the precision diode and is capable of rectifying input signals of
the order of millivolt where the conventional diode cannot rectify below 0.7V18.
18. What is hysterisis? What parameters determine the hysterisis?
(or) What is hysteresis and mention the purpose of hysteresis in a comparator? (May 2015)
If positive feedback is added to the comparator circuit, gain can be increased greatly. Consequently,
the transfer curve of comparator becomes more close to ideal curve. Theoretically, if the loop gain - AOL is
adjusted to unity, then the gain with feedback, A Vf becomes infinite. This results in an abrupt (zero rise time)
transition between the extreme values of output voltage. In practical circuits, however, it may not be possible to
maintain loop gain exactly equal to unity for a long time because of supply voltage and temperature variations.
So a value greater than unity is chosen. This gives an output waveform virtually discontinuous at the
comparison voltage. This circuit, however, now exhibits a phenomenon called hysterisis or backlash.
Parameters which determine the hysteresis are upper threshold VUT and lower threshold VLT.

19.Draw the circuit diagram of an op-amp differentiator circuit. (Nov 2012)

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ISO9001:2008

EC6404 Linear Integrated Circuits

Department of ECE

2016-2017

Vout= -RC (dVin/dt)

20. How does precision rectifier differ from the conventional rectifier? (Nov 2012)
(or) State the difference between conventional and precision rectifier? (Nov 2014)
(or)What is the difference between normal rectifier and precision rectifier? (May 2015)
In conventional rectifiers, as long as the input exceeds the cut-in voltage of the diode, it does not conduct. Due
to this, the output is distorted producing cross over distortion. For the input between 0.7V, the output remains
zero which is the main limitation of the conventional rectifier. The open loop gain of the opamp is very large.
Hence for very small amount of the input, it produces large output which makes the diode conduct. Thus the
diode conducts for very small input voltages of the order of millivolts. Hence, the precision rectifiers are very
precise.
21. Give an application of inverting amplifier. (May 2013)
Differentiator, Integrator, Rectifiers, Summer.
22. What is a window detector?
A window detector is one which is used to mark the instant at which an unknown input is between two threshold
levels.
23. What is a voltage follower? (May 2014)
It is a circuit in which the output voltage follows the input voltage i.e. the output voltage is same as that of the
input voltage.

Gain

Rf
V0
1
1 0 1
Vi
R1

HenceV0 Vi

24. Draw a non-inverting amplifier with voltage gain of 3.(Nov 2013)

Gain

Rf
V0
1
3
Vi
R1

Let R1 1k
R f 2k R1 2k

25. Draw the circuit diagram of peak detector. (May 2014)

26. Determine the output voltage for the circuit shown in fig when
(a) Vin = -2V (b) Vin = 3V. (Nov 2015)
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ISO9001:2008

EC6404 Linear Integrated Circuits

Department of ECE

2016-2017

If Vin > Vref ; Vout = +Vcc

If Vin < Vref ; Vout = -Vcc

27. Plot the transfer characteristics of the circuit shown below, the opamp saturates at 12V. (Nov 2015)

28. Calculate the output voltage for the circuit shown below. (May 2016)

Vo = Rf (V1 V2) / Ri

PART B
1. With neat circuit diagram and mathematical expressions, explain the operation of the following op-amp
applications: (i) Scale changer (4) (ii) Voltage follower (4) (iii) Non inverting adder (4) (iv) Integrator (4)
(April 2011, Nov 2012)
2. With the help of circuits and necessary equations, explain how log and antilog computations are performed
using IC 741. (16) (April 2011, Nov 2012, May 2014, May 2016)
3. (i) What do you understand by an instrumentation amplifier. (2)
(ii) State the requirements of a good Instrumentation Amplifier. (4)
(iii) Draw the circuit diagram and explain the working of instrumentation amplifier.(6) (Nov 2013)
(iv) Mention the specific advantages and application of three op-amp Instrumentation Amplifier circuit.(4)
(May 2013, Nov 2014, May 2016)
4. (i) What do you understand by an Integrator? (2) (May 2013)
(ii) Draw and explain an ideal active op-amp Integrator circuit. (4)
(iii) Draw the I/O waveforms for integrator (3 = 1 )
(iv) Derive the expression for change in output voltage. (3)
(v) List the applications of practical Integrator. (1 )
(vi) Design a practical integrator circuit with a dc gain of 10, to integrate a square wave of 10 KHZ
5. With neat diagram explain the application of op-amp as precision rectifier, clipper, and clamper. (Nov 2013,
May 2014, Nov 2014, Nov 2015)
6. Explain the operation of comparator with a neat diagram and its types. Derive the expression for V H and also
draw the transfer characteristic of comparator.
7. (i) Determine the rate of change of the output voltage in response to the first input pulse as shown below for
the integrator. The output voltage is initially zero. Also, describe the output after the first pulse. Draw the output
waveform. (8)

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EC6404 Linear Integrated Circuits

Department of ECE

2016-2017

(ii) Explain in detail about the V to I and I to V converters. (8) (May 2015, Nov 2015)
8. (i) With neat diagram explain the operation of Schmitt trigger. (8)
(ii) Design a wide band pass filter having f L=400Hz, fH = 2 KHz and pass band gain of 4. Find the value of
Q factor. (8)(Nov 2010, Nov 2011, May 2012, Nov 2013, May 2015)
9. Mention two advantages of active filter over passive filter. Also design an op-amp based second order active
low pass filter with cut-off frequency 2KHz. (8) (Nov 2011, May 2012, Nov 2015)
10. (i)Design a circuit to implement V0=0.545V3+0.273V4-1.25V1-2V2 (8)
(ii)Draw and explain a simple Op-amp differentiator. Mention its limitations. Explain with a neat diagram
how it can be overcome in a practical differentiator. Design an op-amp differentiator that will differentiate an
input signal with maximum frequency fmax=100Hz (8) (April 2010, May 2012, Nov 2015)
11. (i) Design a second order high pull butter worth filter having cut-off frequency of 5kHz. (6)
(ii) What is precision rectifier? With circuit schematic explain the working principle of full wave rectifier. (6)
(iii) Determine the output voltage for the following circuit. (4) (May 2016)

UNIT III: ANALOG MULTIPLIER AND PLL

PART-A
1. List the basic building block of a PLL.
The basic building blocks of a PLL are phase detector, low pass filter, error amplifier and a voltage controlled
oscillator.
2. Define Capture range, Lock in range, Pull in time. (Nov.2012, Nov 2015)
Capture range: The range of frequencies over which the PLL can acquire lock with an input signal is called the
capture range.
Lock in range: The range of frequencies over which the PLL can maintain the lock with the incoming signal is
called lock-in-range.
Pull-in-time: The total time taken by the PLL to establish lock is called pull in time. This depends on the initial
phase and frequency difference between the two signals as well as on the overall loop gain and loop filter
characteristics.
3. List the applications of the PLL. (May 2013)
(or) What are the applications of PLL for AM detection? (May 2015)
Some applications of PLL are: Frequency multiplier, divider, AM and FM demodulator, FSK demodulator.
4. Explain the use of LPF in PLL.
LPF is used in PLL to remove high frequency components and noise, Control the dynamic characters (capture
range, lock range band width& transient response), provide a short time memory (given by the charge on the
filter capacitor), provides a high noise immunity and locking stability.
5. What is a multiplier?
A multiplier produces an output Vo proportional to the product of two inputs Vx and Vy.
Vo=K Vx Vy Where K is the scale factor.
6. What is the basic principle of VCO? (Nov 2012)
Voltage controlled oscillator (VCO) is a free running multivibrator and operates at a set frequency f o. It is
determined by an external timing capacitor and resistor .The frequency is shifted by applying a dc voltage Vc
and is proportional to it. Hence, it is called voltage controlled oscillator. The applied input voltage determines
the instantaneous oscillation frequency. Consequently, modulating signals applied to control input may
cause frequency modulation (FM) or phase modulation (PM). A VCO may also be part of a phase-locked loop.
7. What is a four quadrant multiplier? (May 2016)
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ISO9001:2008

EC6404 Linear Integrated Circuits

Department of ECE

2016-2017

A multiplier that accepts input of either polarity and preserves the correct polarity relationship at the output is
called a four quadrant multiplier.
8. Explain the basic principle of PLL. (May 2014)
PLL is a frequency selective circuit designed to synchronize with an incoming signal and maintain
synchronization in spite of noise or variations in the incoming signal frequency.

9. List the advantages of a variable transconductance technique.

Simple to integrate into monolithic chip, provides very good accuracy, very cheap hence economical, provides
four quadrant operation, provides high speed of operation which is 2 to 3 times more than the logarithmic
method, reduced error at least by 10, reduced error at least by 10 times and the bandwidth of 10 MHz and
higher are available.
10. Draw the block diagram of AM demodulation.

11. Define voltage to frequency conversion factor.

An important parameter for VCO is the voltage to frequency conversion factor. (Kv) is defined as Kv =
(fo/Vc), Where Vc is the modulating voltage required to produce the frequency shift fo for a VCO.
12. What is a phase detector? What are its types?
Phase detector is a multiplier, which produces the sum (fs+fo) and difference (fs-fo) components at its output.
There are two types of phase detector namely, Analog and digital .
13. Draw the transfer characteristics of PLL.

14. Explain the features of 566 VCO.

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2016-2017

Wide supply voltage range 10V to 24V, High temperature stability, Linear modulation, characteristics,
Frequency can be controlled by means of current, voltage, resistor or capacitor.
15.How voltage output of a PLL can be used as frequency discriminator? (or) Draw the circuit diagram
of a PLL using as a FM Detector. (May 2016)
When PLL is locked to an input frequency, the error voltage Vc(t) is proportional to (fs-fo).If the input
frequency is varied as in the case of FM signal, V e will also vary in order to maintain the lock. Then the volt
output serves as a frequency discriminator, which converts the input frequency changes to voltage changes.

16. What is the function of modulating input voltage in VCO?

Voltage input controls the resonant frequency
17. List any 4 applications of VCO
Function generators, The production of electronic music, to generate variable tones, Phase-locked loops,
Frequency synthesizers used in communication equipment.
18. What is a two quadrant multiplier? (Nov 2012)
If one of the input signals is fixed, and the other may have either polarity, the multiplier is called a two quadrant
multiplier and its output may have either polarity (and is bipolar).
19. A PLL frequency multiplier has an input frequency of f and a decade counter is included in the
loop. What will be the frequency of the PLL output. (May 2013)
Frequency of PLL output is f/10.
20. What are the applications of PLL as voltage output and as frequency output?
Voltage output is used in frequency discriminator applications where as the frequency o/p in used in signal
conditioning, frequency synthesis or clock recovery applications.
21. What is meant by frequency synthesizing and its need? (Nov 2013, May 2014)

A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single
fixed time base or oscillator. They are found in many modern devices, including radio receivers, mobile
telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems, etc. A frequency
synthesizer can combine frequency multiplication, frequency division, and frequency mixing (the frequency
mixing process generates sum and difference frequencies) operations to produce the desired output signal.
22. Define lock range of a PLL. (Nov 2013)
The range of frequencies over which a PLL can maintain lock with the input signal is called lock-in-range.
23. How do you convert a basic multiplier to a squaring and square root circuit? (May 2015)
Square
circuit

Square
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circuit

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2016-2017

24. What is the function of a phase detector in a PLL? (Nov 2014)

A phase detector or phase comparator is a frequency mixer, analog multiplier or logic circuit that generates a
voltage signal which represents the difference in phase between two signal inputs. It is an essential element of
the phase-locked loop (PLL).
25. Define modulation index. (Nov 2014)
The modulation index (or modulation depth) of a modulation scheme describes by how much the modulated
variable of the carrier signal varies around its unmodulated level. It is defined differently in each modulation
scheme.
26. Mention two applications of Analog multiplier. (Nov 2015)
Applications: Squarer, Square rooter, Frequency doubler etc.

PART B
1. Derive an expression for the frequency of the output waveform generated of VCO. Also define the Voltage
to frequency conversion factor and obtain its equation .(16) (Nov 2010, April 2010, April 2011, Nov 2012)
2. i) Explain how IC 565 PLL can be used as a FSK demodulator.(6) (Nov 2011, May 2013, May 2014)
ii) Draw the circuit of a PLL used as AM detector and explain its operation.(6) (April 2011, Nov 2012,
May 2014, Nov 2015)
3. Explain with diagram how PLL can be used as
(i)FM detector (8) (Nov 2013, June 2014, Nov 2015),
(ii)Frequency synthesizer (Explain principle, characteristics and working) (8) (May 2012, May 2013, May
2016)
4. (i) What do you mean by variable Transconductance Analog multiplier? (3)
(ii) State the advantages of variable Transconductance technique for analog multiplication. (5)
(iii) Draw the circuit and explain the working of one quadrant variable transconductance analog
multiplier.(8) (May 2013, May 2015)
5. Explain the working of Analog multiplier using emitter coupled transistor pair. Discuss the applications of
analog multiplier IC. (May 2014).
6. What are important building block of phase locked loop (PLL) and explain its working?(16) (Nov 2010,
Nov 2011, Nov 2013, May 2015, May 2016)
7. With suitable block diagram, explain the operation of 566 voltage controlled oscillator. (Nov 2010, April
2010, April 2011, Nov 2012, Nov 2014)
8. (i)List and define the various performance parameters of a multiplier IC. (8) (May 2012)
(ii)Explain the application of VCO for FM generation. (6) (Nov 2014, (May 2015)
9. Define capture range and lock range. Explain the process of capturing the lock and also derive for capture
range and lock range. (Nov 2010, Nov 2011, Nov 2013, May 2015, Nov 2015)
10. (i) Explain, with necessary equations, the basic circuits of Linearized transconductance multiplier and
Differential V-I convertor. Hence explain the Four quadrant variable transconductance multiplier circuit.
(10) (Nov 2012, May 2016)
(ii) Explain the working of Gilbert multiplier cell (5) (Nov 2013)
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UNIT IV ANALOG TO DIGITAL AND DIGITAL TO ANALOG

CONVERTERS
PART-A
1. Why do we prefer digital form rather than analog form?
For processing, transmission and storage purposes, it is more convenient to express information carrying signals
such as voltage, current, pressure (analog form) in digital form. When expressed in digital form, they provide
better accuracy and reduce noise.
2. Explain the necessity of a sample and hold circuit?
For accurate analog to digital conversion the analog input voltage should be held constant during the conversion
cycle. If the analog input voltage changes by more the +1/2 LSB an error can occur in the digital output code.
To minimize the occurrence of error, sample and hold circuits are used.
3. Write the basic principle of sample and hold circuits. (Nov 2013, May 2014)
The sample and hold circuit samples the value of the input signal in response to a sampling command and hold
it at the output until arrival of the next command. It samples an analog input voltage in a very short period and
holds the sampled voltage level for an extended period.

4. Give the applications of the S/H circuit (or) Give the applications of sample and hold circuit. (Nov
2014)
Digital interfacing, A/D converter circuits, Pulse modulation systems, In analog DEMUX.
5. Define resolution of a DAC. (Nov 2014)
Resolution is the number of different analog output values that can be provided by a DAC. For an n-bit DAC,
Resolution=2n. Resolution is also defined as the ratio of a change in output voltage resulting from a change of
1LSB at the digital inputs. For an n-bit DAC, Resolution=VOFS / (2n-1); VOFS-Full scale output voltage.
6. Define accuracy of a DAC.
Accuracy is a comparison of actual output voltage with expected output. It is expressed in percentage. Ideally
the accuracy of the DAC should be, at worst + LSB.
Accuracy = VOFS / ((2n-1)* 2)
7. Define conversion time of a DAC. Also define settling time of a DAC.
Conversion time is the time required for conversion of analog signal into its digital equivalent.
Settling time is time required for the output of the DAC to settle to within + LSB of the final value for a
given digital input i.e. 0 to full scale. Settling time ranges from 100ns to 10s depending and type of circuit
used.
8. What are the drawbacks of binary weighted resistor D/A converter? (Nov 2012)
Wide range of resistor values are required, It is impracticable to fabricate large values of resistance in IC and
voltage drop across such large resistors due to this bias current also affects accuracy.
9. Give the advantages of R/2R ladder DAC. (or) Mention two advantages of R/2R ladder DAC when
compared to weighted resistor type DAC. (Nov 2015)
Easier to build accurately as only two precision metal film resistors are required whereas in weighted resistor
type DAC, a wide range of resistor values are required, it is impracticable to fabricate large values of resistance
in IC. No. of bits can be expanded by adding more sections of same R/2R values. In inverted R/2R ladder DAC
node voltages remain constant with changing input binary words. This avoids any slow down effects by stray
capacitances.
10. Write the principle involved in successive approximation ADC.
In this technique, the basic idea is to adjust the DACs input code such that its output is within + LSB of
the analog input Vi to be A/D converted. The successive approximation method uses very efficient code
searching strategy called binary search. It completes searching process for n bit conversion in just n clock
periods.
11. Which type of ADC is the fastest and why?

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Flash A/D converter also known as the simultaneous or parallel comparator is the fastest of all ADCs because
the fast conversion speed is accomplished by providing 2 n-1 comparators and simultaneously comparing the
input signals with unique reference levels spaced one LSB apart.
12. What are the disadvantages of delta modulation?
Granular noise: The granular noise occurs when the step size is too large when compared to small variations in
the input signal.
Slope overload distortion: The slope overload distortion occurs when the rate of change of the analog waveform
is too high for the staircase waveform to follow.
13. What are the advantages of Adaptive delta modulation over delta modulation?
The signal to noise ratio is better than ordinary delta modulation because of the reduction in slope overload
distortion and granular noise , Because of the variable step size the dynamic range of ADM is wide , Utilization
of bandwidth is better than delta modulation.
14. What is meant by weighted Resistor type DAC? List out the main disadvantages of Weighted resistor
type DAC.
It is a type of Digital to Analog conversion technique in which various ranges of resistors are used for reference
value for converting a Digital value to its corresponding Analog value. It needs various types and ranges of
resistors which is difficult to maintain in the circuit and also it the presence of so many resistors will create
some problems in the circuit.
15. What is the need for over sampling in Analog to Digital Converters?
In order to avoid distortion of signals at high frequencies we need to take more samples at regular intervals so
for higher rate of sampling we need over samplers.
16. What are the advantages and disadvantages of Flash type ADC?
Flash type ADC are the fastest type of convertors present in the ADC since they use comparison technique it is
also having speed and the disadvantage is that if the comparison is too large it takes more duration to convert.
17. What output voltage would be produced by a D/A converter whose output range is 0 to 10V and
whose input binary number is 0110 for a 4 bit DAC? (Nov 2012)
Output voltage= [(Output range)/2n] x (Decimal equivalent of input binary)
= (10-0)/24 x (6) = 3.75
18. What is the drawback of dual slope ADC? (Nov 2012)
Slow speed, accuracy is dependent on the use of precision external components, high cost.
19. Mention any two specifications of a D/A converter. (May 2013)
a. LM741 op-amp
b. Full scale output=5V
20. For a n-bit flash type A/D converter, how many comparators are required? State the disadvantage of
that type of converter. (or) Determine the number of comparators and resistors required for 8-bit flash
type ADC. (May 2013, Nov 2015)
n- bit flash type A/D convertor requires 2n-1 comparators.
Disadvantages: A Flash converter requires a huge number of comparators compared to other ADCs, especially
as the precision increases. A Flash converter requires 2 n-1 comparators for an n-bit conversion. The size, power
consumption, and cost of all those comparators make Flash converters generally impractical for precisions
much greater than 8 bits (255 comparators).
21.Give any two advantages of SA type ADC.(May 2014)
a) It uses very efficient code searching strategy called binary search.
b) High speed of conversion. Time for one analog to digital conversion is Tc=T(n+1)
where T is the clock period and n is the number of bits.
22. What would be produced by a DAC, whose output range is 0 to 10V and whose input binary number
is 10111100 (for a 8 bit DAC).(May 2015)
Output voltage= [(Output range)/2n] x (Decimal equivalent of input binary)
= (10-0)/28 x (188) = 11.25V
23. State the principle of single slope A/D converter. (Nov 2013)
Initially the reset signal is applied to ramp generator. Then input voltage is applied to the comparator. This
produces a high output. Hence output of AND gate is high. This high output starts the binary counter and the
ramp generator.

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As long as the output of AND gate is high the counter keeps counting. When the output of ramp generator is
lower than analog input, the output of AND is low and the counter stops counter. The value displayed by the
counter is proportional to analog input.
24. What is oversampling? (May 2015)
In signal processing, oversampling is the process of sampling a signal with a sampling frequency significantly
higher than the Nyquist rate. Theoretically, a bandwidth-limited signal can be perfectly reconstructed if sampled
above the Nyquist rate, which is twice the highest frequency in the signal. Oversampling improves resolution,
reduces noise and helps avoid aliasing and phase distortion by relaxing anti-aliasing filter performance
requirements.
25.What are the different classifications of ADC?
SAR Type, Counter Type, Single slope type and dual slope type are the various classifications of ADC.
26. A 12 bit D/A convertor has resolution of 20 mV/LSB. Find the full scale output voltage. (May 2016)
Resolution = Voff / (2n 1)
27. Draw the binary ladder network of DAC. If the value of the smallest resistance is 10k, what is the
value of the other resistance? (May 2016)
R = 10k; VR = 10V; n=3
For value of 1 LSB = 0.5V
(Rf x VR) / (R x 2n) = 0.5

PART B
1. Describe the operation of dual slope and successive approximation type ADC. What are the advantages of
2.

3.
4.
5.
6.
7.

8.

9.

dual slope ADC? (Nov 2010, April 2010, April 2011, Nov 2012, May 2014, May 2015, Nov 2013, May
2016)
(i)Explain voltage mode and current mode operations of R-2R ladder type DAC. Compare performance of
various DACs (8) (April 2010, Nov 2010, April 2011, May 2014, May 2016)
(ii)Explain the operation of sample and hold circuit with circuit diagram and write its application and
significance.(8) (Nov 2010, April 2010, Nov 2011, May 2016)
A dual slope ADC uses a 16-bit counter and a 4MHZ clock rate. The maximum input voltage is +10V. The
maximum integrator output voltage should be -8V when the counter has recycled through 2 n counts. The
capacitor used in the integrator is 0.1 F. Find the value of resistor R of the integrator.(8) (April 2010)
Explain the following DAC with suitable circuit diagram:(Nov 2011)
(i)Binary weighted resistor DAC (8)
(ii)Inverted R-2R Ladder DAC (8) (April 2011, Nov 2012, Nov 2013, Nov 2014, May 2015)
Draw the circuit of flash type ADC and explain. (or) With a neat block diagram, explain the working 2-bit
flash type ADC. (Nov 2014, Nov 2015)
Explain the oversampling A/D converter with functional block diagram.(8)(April 2011)
(i)Explain the following types of electronic switches used in D/A converter, with suitable diagrams:
1) Totem pole MOSFET switch (4) 2) CMOS inverter as a switch (4) (May 2016)
(ii)Explain the working of R-2R ladder DAC, by taking example of a 3-bit DAC circuit. Sketch the
corresponding equivalent circuits and hence obtain the equation for the output (8)
(i)Explain over sampling A/D convertor with functional block diagram(8) (Nov 2012)
(ii) Compare single slope ADC and dual slope ADC. (3)
(iii)For a particular dual slope ADC, t 1 is 83.33ms and the reference voltage is 100mv. Calculate t 2 if V1 is
100 mv and 200 mv. (5) (May 2013)
Draw the block diagram and explain the working of :
(i) Charge Balancing VFCS. (8)
(ii)Voltage to Time converter. (8) (May 2013)

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10. Explain Flash type, single slope and dual slope ADC. Give a table of comparison of flash, Dual slope and
successive- approximation ADC, in terms of parameters like speed, accuracy, resolution, input-hold-time.
(16) (May 2012,May 2014)
11. With a neat block diagram, Explain the working of successive approximation type ADC. Also determine the
conversion time of 8 bit and 16 bit successive approximation type ADC if its clock frequency is 50Hz. (Nov
2015)

UNIT V- WAVEFORM GENERATORS AND SPECIAL FUNCTION ICs

PART-A
1. How do you use timer IC for frequency division operation?
A continuously triggered monostable circuit when triggered by a square wave generator can be used as a
frequency divider, if the timing interval is adjusted to be longer than the time period of the triggering
square wave input signal.
2. Draw an astable multivibrator using a timer IC with normally ON load

3. Differentiate between linear and switching regulator

Linear regulator
Switching regulator
Here the pass transistor is operated
Here the pass transistor is used as controlled switch
in its linear region to provide a
and is operated at either cutoff or saturated state.
controlled voltage drop across with Hence the power transmitted across the pass device is
a steady dc current flow .
discrete pulses rather than a steady current flow
4. What is a three terminal regulator?
78XX series are three terminal positive fixed voltage regulators. there are seven output voltage options
available such as 5,6,7,8,12,15,18 and 24V in 78XX the last two XX indicate the output voltage .
5. How can a three terminal voltage regulator IC circuit be modified to provide variable voltage output?
To provide variable voltage output the ground terminal of the fixed three terminal voltage regulator is floating.
They are those, which provide a dc voltage independent of the load current, temperature and ac line voltage
variations.
6. List and explain the characteristics of a three terminal voltage regulator IC.
1. Output Voltage Vo: The regulated output voltage is fixed at a value as specified by the manufacturer. There
are a number of models available for different output voltages, for example, 78XX series has output.
2.|Vin| >= |V0| + 2V,
3. Io max,
4. Thermal shut down
7. Explain the current limiting features of 723 regulator.
Current limiting refers to the ability of a regulator to prevent the load current from increasing above a preset
value. The characteristic curve of a current limited power supply is shown below. The output voltage remains
constant for load current below I limit. As current approaches this limit, the output voltage drops. The current limit
Ilimit is set by connecting an external resistor R sc between the terminals CL and CS terminals shown below. The
CL terminal is also connected to the output terminal Vo and CS terminal to the load.
8. What is the principle of SMPS?
The pass transistors in SMPS are switched ON and OFF at 20 KHz or faster. The output level is controlled by
varying the pulse width of the switching waveform. Operating at this frequency allows the use of smaller
transformers, capacitors, and inductors.
9. What is the advantage of a switched capacitor filter? (Nov.2012)
In a switched capacitor filter, large value of a resistor is realized by switching a capacitor.
10. Give performance parameters or important characteristics for opto-isolators.
i)Current Transfer Ratio (CTR) ii)Isolation voltage between input and output (Viso)
iii)Response Time iv)Common mode rejection v)VCE(max)
vi)IL(max)
vii)Bandwidth
11. How are optocouplers superior to electrical coupling?
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A circuit connected to the input of an optocoupler can be electrically fully isolated from the output circuit.
Therefore, a potential difference of 100s or 1000s of volts can safely exists between two circuits without
adversely influencing the optocoupler action.
12. State the application of 555 timer IC. (Nov 2013)
Timer circuit, Pulse generation, Oscillators, IR transmitter/receiver.
13. What is a switched capacitor filter?
Switched capacitor filter employs analog sample data techniques. The accuracy of the signal processing
function depends on the accuracy of the capacitor ratios. The switched capacitor filters are all IC circuits. They
were developed through the simulation of resistors by operating MOS capacitors with MOS switches.
14. Give the formula for period of oscillations in an op-amp astable circuit. (May 2013)
Period of the Oscillation = 2RC* logn [(RA+2RB)/RA]
15. Draw the functional block diagram of 723 Regulator. (May 2015)

16. Draw the block diagram of a voltage to frequency converter.

17. What is power amplifier?(Nov.2012)

Power amplifier is used to amplify audio signals. The amount of power handling capacity is high for power
amplifiers. The loads to such amplifiers are generally load speakers and servomotors. Power amplifiers develop
and feed sufficient power to loads like speakers, motors etc by handling large signals, hence they are also called
large signal amplifiers.
18. What are the limitations of IC723 general-purpose regulator. (Nov 2012)
The step down transformer used in the power supply circuit is bulky and it is the most expensive component of
the circuit. Large values of filter capacitors are required to eliminate ripples due to low line frequency of
operation. The efficiency of series regulator is less than 50%. The input voltage must be more than the required
output regulated voltage. The difference between the input and output voltage drops across the linear pass
transistor and dissipates power.
19. Define duty cycle of a periodic pulse wave form. (May 2013)
Duty cycle is defined as the ratio of pulse width to the total pulse period, expressed as percentage. Duty
cycle=Ton/(Ton+Toff) x 100
20. Define line regulation with respect to a voltage regulator. (Nov 2013)
Line regulation is the capability to maintain a constant output voltage level on the output channel of a power
supply despite changes to the input voltage level.
21. List the types of multivibrators. (May 2014)
a)Monostable multivibrator using 555 timer, b)Astable multivibrator using 555 timer.
22. What is an opto coupler? (May 2014)

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The combined package of LED and photodiode is called opto coupler. When V 1 is changed the current I 1 in the
input circuit changes and thus the light emitted by LED also change. This light falls on photo diode and hence
produces corresponding current in the output circuit. Thus the current I 2 in the output circuit also changes. The
output voltage is the potential difference between V2 and drop across R2. Thus, the change in input voltage
produces a corresponding change in output voltage.
23. Define line and load regulation of a regulator. (Nov 2014)
Line regulation is the ability to maintain a constant output voltage level on the output channel of a power
supply despite changes to the input voltage level. Load regulation is the capability to maintain a constant
voltage (or current) level on the output channel of a power supply despite changes in the supply's load (such as
a change in resistance value connected across the supply output)
24. What are the different protection circuits inside the monolithic IC regulators? (Nov 2014)
Short circuit and Over voltage protection, Thermal shutdown, Reverse battery and Reverse transient protection.
25. State the two conditions for oscillation. (May 2015)
|A| = 1,
Angle (A) = 0o or 360o
26. What is an isolation amplifier? Mention its applications. (May 2016)
Isolation amplifiers are a form of differential amplifier that allow measurement of small signals in the
presence of a high common mode voltage by providing electrical isolation and an electrical safety barrier.
They protect data acquisition components from common mode voltages, which are potential differences
between instrument ground and signal ground. Its applications are Industrial process control, transducer
sensing, motor and SCR control, Ground loop elimination, biomedical measurements, test equipments and
data acquisition.
27. What is the purpose of connecting a capacitor at the input and output side of an IC voltage regulator.
(Nov 2015)
Input capacitance is used to cancel the inductive effects due to long distribution leads. Output capacitance is
used to improve the transient response.
28. Mention two applications of Frequency to voltage converter. (Nov 2015)
Frequency-to-voltage converters are used in a variety of industries and applications. For example, vehiclemonitoring applications use frequency-to-voltage converters to evaluate the response times of clutches, airconditioning compressors, and anti-lock braking systems. Frequency-to-voltage converters are also used in
driveline analysis and to monitor and control engine speeds. Other applications for frequency-to-voltage
converters include flow meter monitoring, machine analysis and control, and response time evaluation.

PART B
1. Describe the working of IC723 voltage regulator and explain the importance of current limiting techniques.
Also, state the need for isolation amplifier. (Nov 2013, May 2014, May 2016)
2. (i) Explain the working of astable and mono stable multi vibrator using IC555 timer. (or) Describe
monostable multivibrator with necessary diagrams using IC 555 and derive for the expression for frequency
of oscillation with relevant to the waveforms. (12)(Nov 2013, Nov 2014, Nov 2015)
(ii) A 555 timer is configured in Astable mode with R A = 2k, RB = 6k and C = 0.1F. Determine the
frequency of oscillation. (4) (May 2016)
3. With a neat diagram, explain the working of step up and step down switching regulators. (Nov 2014)
4. With neat diagrams, explain the operation of frequency to voltage converters and voltage to frequency
converters.
5. (i)Explain the working and functionalities of LM 380 power audio amplifier. (8)(Nov 2012, May 2016)
(ii)Draw the schematic of linear IC saw tooth waveform generator and explain its operation. (8)(May 2016)
6. With a suitable diagram, explain the working of following:
(i) Video amplifier (8)(Nov 2012)
7. State the advantages of IC voltage regulator. Explain the features and internal structure of general purpose
Linear IC 723 Regulator. Design a regulator using IC 723 to meet the following specifications: V 0=5V;
I0=100mA; Vin=1520 %; Isc=150mA; Vsense=0.7V. (16 marks) (May 2013)
8. (i)Design a phase shift oscillator to oscillate at 100Hz.(6)
(ii) Describe Monostable multivibrator with necessary diagrams and derive for ON time and recovery time.
(10) (May 2015)
9. Briefly describe about monolithic switching regulators. (Nov 2012, May 2014,May 2015)
10. Describe astable multivibrator with necessary diagrams using op-amp and derive for the equation for period
of oscillation and also draw its waveform.
11. With a neat circuit diagram, explain the working of linear voltage regulator using operational amplifier. (Nov
2015)

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