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# Important Questions and Answers: Linear Integrated Circuits : Analog Multiplier and PLL

Linear Integrated Circuits ( LIC ) Subject : Analog Multiplier and PLL - Question Bank, Important Questions and Answers

ANALOG MULTIPLIER AND PLL

PART-A

1. List the basic building blocks of PLL

1. Phase detector/comparator

2. Low pass filter

3. Error amplifier

4. Voltage controlled oscillator

2. Define FSK modulation.

FSK is a type of frequency modulation, in which the binary data or code is transmitted by means of a carrier frequency that is shifted between two fixed frequencies namely mark (logic1) and space frequency (logic 0).

3. What is analog multiplier?

A multiplier produces an output v0, which is proportional to the product of two inputs vx and vy V0= kvxvy

4. List out the various methods available for performing for analog multiplier.

• Logarithmic summing technique

• Pulse height /width modulation technique

• Variable Tran’s conductance technique

• Multiplication using gilbert cell

• Multiplication technique using Trans conductance technique

5. Mention some areas where PLL is widely used.

2. Satellite communication systems

3. Air borne navigational systems

4. FM communication systems

5. Computers.

6. What are the three stages through which PLL operates?

1. Free running

2. Capture

3. Locked/ tracking

7. Define lock-in range of a PLL.

The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lock-in range or tracking range. It is expressed as a percentage of the VCO free running frequency.

8. Define capture range of PLL.

The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range. It is expressed as a percentage of the VCO free running frequency.

9. Define Pull-in time.

The total time taken by the PLL to establish lock is called pull-in time. It depends on the initial phase and frequency difference between the two signals as well as on the overall loop gain and loop filter characteristics.

10. Write the expression for FSK modulation.

∆vf=f2-f1/k0

11. Define free running mode.

An interactive computer mode that allows more than one user to have Simultaneous use of a program.

12. For perfect lock, what should be the phase relation between the incoming signal and VCO output signal?

The VCO output should be 90 degrees out of phase with respect to the input signal.

13. Give the classification of phase detector:

1. Analog phase detector.

2. Digital phase detector

14. What is a switch type phase detector?

An electronic switch is opened and closed by signal coming from VCO and the input signal is chopped at a repetition rate determined by the VCO frequency. This type of phase detector is called a half wave detector since the phase information for only one half of the input signal is detected and averaged.

15. What is a voltage controlled oscillator?

Voltage controlled oscillator is a free running multivibrator operating at a set frequency called the free running frequency. This frequency can be shifted to either side by applying a dc control voltage and the frequency deviation is proportional to the dc control voltage.

16. Define Voltage to Frequency conversion factor.

Voltage to Frequency conversion factor is defined as,

Kv = fo / Vc= 8fo /Vcc

Vc is the modulation voltage fo-frequency shift

17. What is the purpose of having a low pass filter in PLL?

*It removes the high frequency components and noise.

*Controls the dynamic characteristics of the PLL such as capture range, lock-in range, band-width and transient response.

*The charge on the filter capacitor gives a short- time memory to the PLL

18. Discuss the effect of having large capture range.

The PLL cannot acquire a signal outside the capture range, but once captured, it will hold on till the frequency goes beyond the lock-in range. Thus, to increase the ability of lock range, large capture range is required. But, a large capture range will make the PLL more susceptible to noise and undesirable signal.

19.Mention some typical applications of PLL:

• Frequency multiplication/division

• Frequency translation

• AM detection

• FM demodulation

• FSK demodulation.

20. What is a compander IC? Give some examples.

The term companding means compressing and expanding. In a communication system, the audio signal is compressed in the transmitter and expanded in the receiver. Examples: LM 2704-LM 2707; NE 570/571.

21. What are the merits of companding?

*The compression process reduces the dynamic range of the signal before it is transmitted.

*Companding preserves the signal to noise ratio of the original signal and avoids non linear distortion of the signal when the input amplitude is large.

*It also reduces buzz, bias and low level audio tones caused by mild interference.

22. What is a VCO?

VCO is a free running multivibrator which operates at free running frequency.

23.Draw the relation between the capture ranges and lock range in a PLL.

24. What is lock range and capture range of PLL?

Range of frequencies over which PLL can maintain lock with the incoming signal is called lock range. Range of frequencies over which PLL can acquire lock with the incoming signal is called capture range.

25. With reference to a VCO, define voltage to frequency conversion factor Kv.

Kv = ∆fo / ∆Vc

26. What are the advantages of variable transconductance technique?

1. Provides four quadrant operation.

2. Good accuracy.

3. High speed operation.

4. Less error.

27.VCO is called  v-f  converter?  why?

The frequency deviation is directly proportional to the dc control voltage and hence it is called a V-f converter.

28. 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?

Output of PLL = 10f

29. Mention any two applications of PLL.

Frequency Translation & AM Detection.

30. What is meant by Frequency synthesizing.

Large number of desired frequencies can be produced from a single crystal controlled oscillator

32. What is the need for Frequency Synthesizer.

To produce precise series of frequencies from a stable crystal oscillator

33. What is the function of phase detector in PLL?

The phase detector produces a DC or low frequency signal which is proportional to the phase difference between the input signal and VCO output signal

34. Under what condition the gilbert cell will function as a multiplier?

When both the input to the gilbert cell are very small, it will work as a multiplier.

35. How do you convert a basic multiplier to a squaring and square root circuit?

When the input is connected to both the terminals of the multiplier IC, it will act as a squaring circuit

36. Mention two application of analog multiplier.

Gilbert cell ,two and four quadrant multiplier.

37. With the equations, show how is a multiplier cab be used for finding phase angle difference between two signals.

38. What is four quadrant multiplier?

39. Draw the circuit diagram of PLL circuit using as a FM detector. 40. Define free running mode.

In a PLL if the error control voltage is zero then the PLL is said to be operated in free running mode and its output frequency is called its center frequency f0.

41. What is a four quadrant multiplier?

In a multiplier circuit, if both the inputs are allowed to swing in both positive and negative directions the multiplier is called as a four quadrant multiplier.

42. Mention some areas where PLL is widely used.

·           Satellite communication systems

·           Air borne navigational systems

·           FM communication systems

·           Computers.

43. List the basic building blocks of PLL

·           Phase detector/comparator

·           Low pass filter

·           Error amplifier

·           Voltage controlled oscillator

44. What are the three stages through which PLL operates?

·           Free running

·           Capture

·           Locked/ tracking

45. Define lock-in range of a PLL.

The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lock-in range or tracking range. It is expressed as a percentage of the VCO free running frequency.

46. Define capture range of PLL.

The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range. It is expressed as percentage of the VCO free running frequency.

47. Define Pull-in time.

The total time taken by the PLL to establish lock is called pull-in time. It depends on the initial phase and frequency difference between the two signals as well as on the overall loop gain and loop filter characteristics.

48. Mention some typical applications of PLL:

·           Frequency multiplication/division

·           Frequency translation

·           AM detection

·           FM demodulation

·           FSK demodulation.

49. What is a voltage controlled oscillator?

Voltage controlled oscillator is a free running multivibrator operating at a set frequency called the free running frequency. This frequency can be shifted to either side by applying a dc control voltage and the frequency deviation is proportional to the dc control voltage.

50. Define VCO.

A voltage controlled oscillator is an oscillator circuit in which the frequency of oscillations can be controlled by an externally applied voltage.

51. On what parameters does the free running frequency of VCO depend on?

·           External timing resistor, RT

·           External timing capacitor, CT

·           The dc control voltage Vc.

52. Give the expression for the VCO free running frequency.

fo = 0.25 / RT CT

53. Define Voltage to Frequency conversion factor.

Voltage to Frequency conversion factor is defined as,

Ky = fo / Vc= 8fo /Vcc

where, Vc is the modulation voltage required to produce the frequency shift fo

54. Define FSK modulation.

In digital data communication, binary data is transmitted by means of a carrier frequency. FSK employs two different carrier frequencies one for logic 1 and other for logic 0 states ofbinary data signal. This process is called FSK modulation.

PART-B

1. Draw and explain the block diagram of PLL IC 565.

2. Draw and explain the operation of VCO IC 566 and derive the expression for fo.

3. a) Derive the expression for capture range and lock range of PLL.  b) Derive the expression for voltage to frequency conversion factor of VCO.

4. Explain the application AM detector and FSK demodulator using PLL.

5. Explain various types of phase detectors used in PLL.

6. a) Explain the application frequency synthesizer using PLL.

b) What is the function of LPF in PLL?

7. Draw and explain the block diagram of PLL IC 565 and derive its transfer function.

8. Draw and explain the operation of VCO IC 566 and derive the expression for fo.

9. a) Derive the expression for capture range and lock range of PLL.

b) Derive the expression for voltage to frequency conversion factor of VCO.

10. Explain about Analog multiplier IC.

11. Sketch and explain the following applications of multipliers.

1. Squaring

2. Finding square root

3. Frequency doubler

4. Phase angle detector

12. (i) With a neat diagram explain the variable transconductance technique in analog multiplier and give its output equation.  (ii) Briefly explain the working of voltage controlled oscillator.

13. What are important building block of phase locked loop (PLL) explain its Working?

14. Draw the functional block schematic of a NE565 PLL and explain the roles of the low pass filter and VCO. Derive the expression for the capture range and lock in range of the PLL.

15. With suitable block diagram, explain the operation of 566 voltage controlled oscillator. Also derive an expression for the frequency of the output waveform generated.

16.(i)List and define the various performance parameters of a multiplier IC.  (ii) How the multiplier is used as the voltage divider? (iii) How the multiplier is used as the frequency doubler?

17. (i) Explain with neat block diagrams how PLL is used as

(i) AM detector

(ii) FM detector

(iii) Frequency synthesizer

(iv) FSK Demodulation

18. a) i) What do you mean by variable Trans conductance Analog multiplier?

ii) State the advantages of variable Tran‟s conductance technique for analog multiplication.

iii) Draw the circuit and explain the working of one quadrant variable Trans conductance analog multiplier.

19. Draw the block diagram and explain principle of working, characteristics and applications of

i) Frequency synthesizer.

ii) Frequency shift keying (FSK) Demodulator.

20. Explain the working of Gilbert Multiplier cell

21. Explain the principle of operation of PLL?

22. Explain the working of Analog Multiplier using emitter coupled transistor pair. Discuss the application of analog multiplier IC.

23. Explain the application of VCO for FM generation.

24. With neat simplified internal diagram, explain the working principle of Operational Tran‟s conductance amplifier. (OTA).

25. Define capture range and lock range. Explain the process of capturing the lock and also drive for capture range and lock range.

25. Derive the expression for the capture range and lock range of Phase Locked

26. Explain the application of PLL as

(i).Frequency synthesizer

(ii)AM demodulator and

(iii) FM demodulator

27. Explain the working of Analog Multiplier using emitter coupled transistor with circuit diagram.

28. Describe how a PLL could be used as a voltage controlled oscillator.

29. Draw the basic schematic of the PLL and explain its operation.

30. Explain the functional diagram the FSK modulation and demodulation operations using PLL‟s

31. Explain the working principle of four quadrant variable form trasconductance multiplier.

32. Discuss the principle of operation of NE565 PLL circuit.

33. How can PLL be modeled as a frequency multiplier?

34. Design a VCO having the maximum range of 1KHz.Assume power supply Vcc=15V.Required pulse width should not exceed 100µs.

35. Design PLL 565 as a FSK demodulator in telephone data transmission.

36. Design a PLL circuit using IC565 to get free running frequency of 4.5 KHz.,Lock range of 2 KHz, Capture Range of 100Hz.Assume supply voltages of ±10Vare available.Show diagram with all component values.

37. In basic multiplier circuit,calculate the output voltage Vo with input voltages Vi=4V and reference voltage Vref=10V.

38. For a VCO circuit,assume R2=2.2KΩ ,R1=R3 = 15K and C1= 0.001µF.Assume Vcc=12V. Determine i) output frequency ii)the change in output frequency if modulating input Vc is varied from 7 to 8V.

39. Determine the change in dc control voltage Vc during lock, if input signal frequency fs=20KHz,the free running frequency is 21KHz and voltage to frequency transfer coefficient of VCO is 4 KHz/V.

40. A PLL IC565 connected as an FM demodulator has R1=10KΩ, C1= 0.01µF and C2= 0.04µF.The supply voltage is +12 V. Determine the i) Free running frequency ii) Lock in range iii) Capture range.

41. In the given circuit V+= 12V,R2= 1.5K,R1=R3=10K and C1= 0.001µF. i) Determine nominal frequency of output. Ii) Compute modulation in output frequencies if Vc is varied between 9.5 and 11.5V. iii) Draw square wave output waveform if the modulating input is a sinewave.

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Linear Integrated Circuits : Analog Multiplier and PLL : Important Questions and Answers: Linear Integrated Circuits : Analog Multiplier and PLL |