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# Important Questions and Answers: Linear Integrated Circuits : Waveform Generators and Special Function ICs

Linear Integrated Circuits ( LIC ) Subject : Waveform Generators and Special Function ICs - Question bank, Important Questions and Answers

WAVEFORM GENERATORS AND SPECIAL FUNCTION ICS

PART-A

1. Mention some applications of 555 timer

*Oscillator

*pulse generator

*ramp and square wave generator

*mono-shot multivibrator

*burglar alarm

*traffic light control.

2 . List the applications of 555 timer in monostable mode of operation:

*Missing pulse detector

*Linear ramp generator

*Frequency divider

*Pulse width modulation.

3. List the applications of 555 timer in Astable mode of operation:

*FSK generator

*Pulse-position modulator

4. What is a voltage regulator?

A voltage regulator is an electronic circuit that provides a stable dc voltage independent of the load current, temperature, and ac line voltage variations.

5. Give the classification of voltage regulators:

*Series / Linear regulators

*Switching regulators.

6. What is a linear voltage regulator?

Series or linear regulator uses a power transistor connected in series between the unregulated dc input and the load and it conducts in the linear region .The output voltage is controlled by the continuous voltage drop taking place across the series pass transistor.

7. What is a switching regulator?

Switching regulators are those which operate the power transistor as a high frequency on/off switch, so that the power transistor does not conduct current continously.This give improved efficiency over series regulators.

8. What are the advantages of IC voltage regulators?

*low cost

*high reliability

*reduction in size

*excellent performance

9. Give some examples of monolithic IC voltage regulators:

78XX series fixed output, positive voltage regulators

79XX series fixed output, negative voltage regulators

723 general purpose regulators.

10. What is the purpose of having input and output capacitors in three terminal IC regulators?

A capacitor connected between the input terminal and ground cancels the Inductive effects due to long distribution leads. The output capacitor improves the transient response.

11. Define line regulation.

Line regulation is defined as the percentage change in the output voltage for a change in the input voltage. It is expressed in mill volts or as a percentage of the output voltage.

Load regulation is defined as the change in output voltage for a change in load current. It is expressed in millivolts or as a percentage of the output voltage.

13.What is meant by current limiting?

Current limiting refers to the ability of a regulator to prevent the load current from increasing above a preset value.

14. Give the drawbacks of linear regulators:

*The input step down transformer is bulky and expensive because of low line frequency.

*Because of low line frequency, large values of filter capacitors are required to decrease the ripple.

*Efficiency is reduced due to the continuous power dissipation by the transistor as it operates in the linear region

15.What is the advantage of monolithic switching regulators?

*Greater efficiency is achieved as the power transistor is made to operate as low impedance switch. Power transmitted across the transistor is in discrete pulses rather than as a steady current flow.

*By using suitable switching loss reduction technique, the switching frequency can be increased so as to reduce the size and weight of the inductors and capacitors.

16. What is an opto-coupler IC? Give examples.

Opto-coupler IC is a combined package of a photo-emitting device and a photo sensing device. Examples for opto-coupler circuit: LED and a photo diode, LED and photo transistor, LED and Darlington.

Examples for opto-coupler IC: MCT 2F, MCT 2E.

17. Mention the advantages of opto-couplers:

*Better isolation between the two stages.

*Impedance problem between the stages is eliminated.

*Wide frequency response.

*Easily interfaced with digital circuit. *Compact and light weight.

*Problems such as noise, transients, and contact bounce are eliminated.

18. What is an isolation amplifier? Mention it‟s application.

An isolation amplifier is an amplifier that offers electrical isolation between its input

and output terminals.

19. What is the need for a tuned amplifier?

In radio or TV receivers, it is necessary to select a particular channel among all other available channels. Hence some sort of frequency selective circuit is needed that will allow us to amplify the frequency band required and reject all the other unwanted signals and this function is provided by a tuned amplifier.

20. Give the classification of tuned amplifier:

(i) Small signal tuned amplifier

*Single tuned *Double tuned *Stagger tuned

(ii) Large signal tuned amplifier.

21. Write the frequency of oscillation (f0) equation for triangular wave generator  .

f0=R3/4R1C1R2

22. How frequency to voltage converted on OP-AMPS.

A Frequency to voltage converter produces an output voltage, whose amplitude is a function of frequency of the input signal. The input signal may be a sine wave, a square wave or a pulse train. The F/V converter is essentially an FM detector or discriminator.

23. What is video amplifier?

The video or wideband amplifiers are designed to provide a relatively flat gain versus frequency response characteristics for the range of frequencies required to transmit video information.

24. Define Multivibrators. Mention its types.

Multivibrators are regenerative circuits, which are mainly used in timing applications. Based on their operational characteristics they can be classified into

•AstableMultivibrators

• MonostableMultivibrators

• BistableMultivibrators

25. Define AstableMultivibrators.

The astableMultivibrators toggles between one state and the other without the influence of any other external control signal. It is also called as free running multivibrator.

26. Define MonostableMultivibrators

The monostablemultivibrator or one –shot requires an external signal called a trigger to force the circuit into a quasi-stable state for a particular time or delay.

27. What is audio amplifier?

The amplifier receives an input from signal source or from a transducer and gives out an amplified signal to the output device is called an audio amplifier.

28. Define AstableMultivibrators.

The astableMultivibrators toggles between one state and the other without the influence of any other external control signal. It is also called as free running multivibrator.

29. Define MonostableMultivibrators.

The monostablemultivibrator or one –shot requires an external signal called a trigger to force the circuit into a quasi-stable state for a particular time or delay.

30. What is audio amplifier?

The amplifier receives an input from signal source or from a transducer and gives out an amplified signal to the output device is called an audio amplifier.

31. What are the three different wave forms generated by ICL8038?

Sine wave, Square wave & Triangular wave.

32. What is meant by thermal shutdown applied to voltage regulators?

The IC has a temperature sensor which turns off the IC when it becomes too hot. The output current will drop and remain there until IC has cooled significantly.

33. What is an opto-coupler IC? Mention its applications.

It is combined package of LED and Photodiode.

34. Define the duty cycle in Astablemultivibrator using IC 555.

Duty cycle = ( Rb / Ra+2Rb)*100

35. What are the limitations of three terminal regulators

1. No short circuit protection.

2. Output voltage is fixed.

36. What is switched capacitor filter.

A switched capacitor filter is a three terminal element which consists of capacitors, periodic switches and op-amps whose open circuit voltage transfer function represents filter characteristics.

37. Give the formula for period of oscillations in an op-amp as table circuit.

T = 2RC ln(1+β / 1-β)

38. Define duty cycle of a periodic pulse wave form.

Duty cycle = (Rb / Ra+2Rb)*100

39. State the two conditions for oscillations?

1. The loop gain is equal to unity in absolute magnitude and

2. The phase shift around the loop is zero or an integer multiple of 2π

40. Draw the functional diagram of 723 regulator?

41. Define 555 IC?

The 555 timer is an integrated circuit specifically designed to perform signal generation and timing functions.

42. Draw the Pin diagram of IC 555.

43. List the basic blocks of IC 555 timer?

A relaxation oscillator

RS flip flop

Two comparator

Discharge transistor

44. Give the classification of voltage regulators:

Series/ Linear regulator

Switching regulators

45.Mention some applications of 555 timer:

Oscillator

pulse generator

ramp and square wave generator

mono-shot multivibrator

Traffic light control.

46. List the applications of 555 timer in monostable mode of operation:

Missing pulse detector

Linear ramp generator

Frequency divider

Pulse width modulation.

47. List the applications of 555 timer in Astable mode of operation:

FSK generator

Pulse-position modulator

48. What is a multivibrator?

Multivibrators are a group of regenerative circuits that are used extensively in timing applications. It is a wave shaping circuit which gives symmetric or asymmetric square output. It has two states either stable or quasi- stable depending on the type of multivibrator.

49 .What do you mean by monostable multivibrator?

Monostable multivibrator is one which generates a single pulse of specified duration in response to each external trigger signal. It has only one stable state. Application of a trigger causes a change to the quasi -stable state. An external trigger signal generated due to charging and discharging of the capacitor produces the transition to the original stable state.

50.What is an astable multivibrator?

Astable multivibrator is a free running oscillator having two quasi-stable states. Thus, there is oscillations between these two states and no external signal are requi ed to produce the change in state.

51. Give the classification of voltage regulators: What is a voltage regulator?

A voltage regulator is an electronic circuit that provides a stable dc voltage independent of the load current, temperature, and ac line voltage variations.

52. What is a linear voltage regulator?

Series or linear regulator uses a power transistor connected in series between the unregulated dc input and the load and it conducts in the linear region .The output voltage is controlled by the continuous voltage drop taking place across the series pass transistor.

53. What is a switching regulator?

Switching regulators are those which operate the power transistor as a high frequency on/off switch, so that the power transistor does not conduct current continuously. This gives improved efficiency over series regulators.

54. Give some examples of monolithic IC voltage regulators:

78XX series fixed output, positive voltage regulators

79XX series fixed output, negative voltage regulators 723 general purpose regulator.

55. What is the purpose of having input and output capacitors in three terminal IC regulators?

A capacitor connected between the input terminal and ground cancels the inductive effects due to long distribution leads. The output capacitor improves the transient response.

56. Define line regulation.

Line regulation is defined as the percentage change in the output voltage for a change in the input voltage. It is expressed in milli volts or as a percentage of the output voltage.

Load regulation is defined as the change in output voltage for a change in load current. It is expressed in millivolts or as a percentage of the output voltage.

58. What is meant by current limiting?

Current limiting refers to the ability of a regulator to prevent the load current from increasing above a preset value.

59. Give the drawbacks of line r regulators:

The input step down transformer is bulky and expe sive because of low line frequency.

Because of low line frequency, large values of filter capacitors are required to decrease the ripple. Efficiency is reduced due to the continuous power diss pation by the transistor as it operates in the linear region.

60. What is the advantage of switching regulators?

Greater efficiency is achieved as the power transistor is made to operate as low impedance switch.

Power transmitted across the transistor is in discrete pulses rather than as a steady current flow.

By using suitable switching loss reduction technique, the switching frequency can be i creased so as to reduce the size and weight of the inductors and capacitors.

61. Define drop-out voltage of a fixed voltage regulator.

It is the minimum voltage that must exist between input and output terminals. It is defined as the ratio of the r.m.s input ripple voltage to the r.m.s output ripple voltage. It is expressed in decibels (dB).

62. What are the advantages of switched capacitor filters?

Very high high value of resistors can be easily simulated using small value capacitors, of the order of 10pF.

The switched capacitor filters require no external reactive components like inductive capacitors.

Completely active filters can be sily obtained on a monolithic IC chip.

Good temperature stability, high accuracy and low cost

63. Define video amplifier.

A video amplifier has to amplify signals over a wideband of frequencies, say upto 20MHz. It is a RC coupled amplifier with bandwidth from d.c. to high frequency upto few megahertz.

64. What is opto coupler?

An opto-isolator, also called an optocoupler, photocoupler, or optical isolator, is "an electronic device designed to transfer electrical signals by utilizing light waves to provide coupling with electrical isolation between its input and output". The main purpose of an opto-isolator is "to prevent high voltages or rapidly changing voltages on one side of the circuit from damaging components or distorting transmissions on the other side

65. What is LM380?

It is a power amplifier produced by national semiconductor. It is capable of delivering 2.5 W min, to 8 ohm load.

66. Mention the advantages of opto-couplers:

Better isolation between the two stages.

Impedance problem between the stages is eliminated.

Wide frequency response.

Easily interfaced with digital circuit.

Compact and light weight.

Problems such as noise, transients, contact bou ce, are eliminated.

67. What is an isolation amplifier?

An isolation amplifier is an amplifier that offers electr cal isolation between its input and output terminals

68. What are the types of optocouplers?

LED and a photo diode

LED and photo transistor,

LED and Darlington

69. Give two examples of IC optocouplers? -coupler IC

Examples for opto-coupler IC

MCT 2F

MCT 2E

.

70. List the applications of Isolation amplifier.

• Floating pulse amplifier output voltage and current interface

• Instrumentation in high-noise environments.

• Analogue front-end processing.

• Medical instrumentation

71. What is the purpose of connecting a capacitor at the input and the output side of an IC voltage regulator?

The figure above shows the application of LM340 IC as a voltage regulator. Pins 1, 2, and 3 are the input, output and ground.

When there is quite a distance (in cms) from the IC to the filter capacitor of the unregulated power supply, there may occur unwanted oscillations within the IC due to lead inductances within the circuit. In order to remove this unwanted oscillation, the capacitor C1 has to be placed as shown in the circuit. Capacitor C2 is sometimes used to improve the transient response of the circuit.

Any device in the LM 340 series needs a minimum input voltage at least 2 to 3 V greater than the regulated output voltage. Otherwise, it will stop regulating. Furthermore, there is a maximum input voltage because of excessive power dissipation.

72. Mention two applications of frequency to voltage converter.

1. Frequency to voltage converter in tachometers.

2. Frequency difference measurement.

73. Write the advantages of switching regulator over series voltage regulators.

74. List any two features of a fiber optic IC.

75. A Hartely oscillator L1=10mH, L2=5mH and C=200pF.Calculate the frequency oscillation.

fr=1/2π √(LTC)

LT=L1+L2=15mH

fr =91.93 kHz

PART-B

1. Explain in detail the function of 555 timer in astable mode and derive the expression for frequency of oscillation.

2. Explain in detail the function of 555 timer in monostable and derive the expression for frequency of oscillation.   3. Draw the internal functional diagram of 555 timer and explain briefly about each pin.

4. a) Draw and explain the astable operation using 555 to achieve 50% duty cycle and derive the expression for the frequency of Oscillation.

b) Write short notes on Optocouplers?

5. Design a adjustable voltage regulator using IC 723 to obtain positive low voltage and high voltage.

(a) Power amplifiers

(b) Tuned amplifiers

(c) Video amplifiers

7. Draw & explain the internal diagram of IC LM723 voltage regulator.

8. With necessary diagrams explain the operation and applications of LM380 IC.

9. Explain the current limiting and current boosting feature of IC LM723.

10. With neat diagram explain the working of step down switching regulator.

11. Explain about the function generator using IC 8038.

13. Draw & explain the internal diagram of IC LM317 voltage regulator.

14. Draw and explain the principle of saw tooth generator.

15. Draw and explain the operation of a triangular wave generator.

16. With suitable diagram, explain the working of a switched capacitor filter. Also explain how resistor can be realized using switched capacitor filter.

17. With necessary diagrams, explain the operation of frequency to voltage converter.

18. With a neat diagram, explain the working of step down switching regulator.

19.(i) How is voltage regulators classified? Explain a series voltage regulator.

(ii) What is an optocoupler? Briefly explain its characteristics.

20.(b) With a neat circuit diagram and internal functional diagram explain the working of 555 timers in astable mode.

21. (i) How can the current drive capability be increased while using three terminal voltage regulators?

(ii) Design an adjustable voltage regulator circuit using LM317 for the following specifications:

Input dc voltage = l3.5 V

Output DC voltage = 5 to 9 V

22. Describe the working of IC723 voltage regulator and explain the importance of current limiting techniques.

23. Sketch the functional block diagram of the following and explain their working principle (i) IC555 Timer (ii) General purpose voltage regulator

24.(i)Explain the working principle of isolation amplifier.

(ii) Explain the principle of operation of optocouplers .

25. 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: Vo = 5V, Io = 100 mA, Vin = 15 ± 20 %, Isc = 150 mA, Vsense = 0.7V.

26. Write detailed notes on the following

i) Low noise op-amps.

ii) Integrated Fiber optic system.

27. Explain the working of Monostable Multivibrator.

28. Describe the operation of astable multivibrator using op amp.

29. Explain the operation of switching regulator using op-amp.

30. Briefly describe monolithic switching regulators.

31. Design a phase shift oscillator to oscillate at 100Hz

32. Describe monostablemultivibrator with necessary diagrams and derive for ON time

and recovery time.

33. With a neat functional diagram, explain the working of 555 timer as monostable multivibrator and derive an expression for the frequency of oscillation with relevant waveforms.

34. With a neat circuit diagram, explain the working of voltage regulator using operational amplifier .

35. Draw the functional diagram for a low voltage regulator using IC723 and explain its operation.

36. State the production circuit used in voltage regulators and explains them with characteristic curve.

37. Describe the astable mode of operation of IC555 timer and discuss any two applications.

38. Explain how opto-couplers can be used in circuits for isolation.

39. Briefy write the working principle and functionalities of LM 380 audio amplifier.

40. Draw the schematic of a linear IC saw tooth waveform generator and explain the circuit operation

41. Summarize the working principle of IC723 general purpose voltage regulator.

42. A 555 timer is configured in as table mode with RA =2k ohm RB=6k ohm and C=0.1μF.Determine the frequency of oscillation.

43. If an IC 555 timer is used to generate a Ramp voltage with constant collector current of 1 mA, Vcc=15V and C=0.1µF,What would be the slope of the ramp generated? How much is the peak value of the ramp generated? What is the duration of the Ramp?

44. Design a square wave oscillator so that Fo= 1KHz.The op amp is IC741 with dc supply voltage ±15V.

45. Design a triangular wave generator so that Fo= 2KHz and Vo = &Vpp. The opamp is IC1458/772 and supply voltages are ±15V.

46. Using MF5 design a second order butterworth LPF with a cut off frequency of 500Hz and a passband gain of -2. Assume +5V power supply and CMOS clock

47. How a monostable multivibrator can be used as a divide by 2 network considering the frequency of input trigger as 2 KHz.

48. Design an adjustable voltage regulator to satisfy the following specifications. Use LM317 regulator. Output voltage Vo = 5-12 V, Output current Io = 1 A.

49. The teletypewriter uses the frequencies 1070Hz and 1270 Hz for its MODEM. Design the FSK generator circuit for this application.

50. Using opamp design a phase shift oscillator to oscillate at 100Hz.

51. Design a timer which should turn on heater immediately after pressing a push button and should hold heater in ON state for 6 Seconds.

52. Design an Astable multivibrator circuitwhich will flash the electric bulb such that its on time will be 4 seconds and off time will be 2 Seconds.

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