## Digital Communications Slip Test Questions

Slip test-1

1. In a PCM system, if the Quantization levels are increased from 2 to 8,                 i. Find the change in Signal to Quantization Noise ratio.                                ii.Find the change in Transmission Bandwidth.
2.  i. Convert the following signal x(t) = 10 cos (200πt) to a discrete signal x[n] if sampling rate is 1000Hz.                                                                                       ii. Write the advantages of Digital Communication system over Analog Communication system.

PART-B

1. Draw the Basic Block Diagram of Digital Communication System and explain each block in detail.
2. Deduce the expression for Signal to Quantization noise ratio in PCM system.                                                                  Slip test-2
1. A PCM source transmits four samples (messages) with a rate 2B samples /second. The probabilities of occurrence of these 4 samples (messages) are equally likely Find out the information rate of the source.
2. A source produces 26 symbols with equal probability what is the average information produced by this source?

PART-B

1. State Mutual information. Prove any three properties of Mutual information.
2. A source alphabet has 10 symbols with the given probabilities 0.02, 0.04, 0.17, 0.02, 0.16, 0.06, 0.03, 0.27, 0.20, 0.03 construct Shannon-Fano coding and calculate the efficiency.

## Digital Communications Quiz with solutions

UNIT-1

QUIZ

1. The band width  needed to transmit Television video plus audio signals of bandwidth 4.2 MHz using Binary PCM  quantization level of 512 is (  c     )         a. 2 MHz            b. 25.6MHz                        c.37.8MHz                    d.75.6MHz
2. A signal m(t)has a bandwidth of 1.0 KHz and exhibits a maximum rate of change of 2.0 volts/sec. The signal is sampled at a sampling frequency of 20 KHz and quantized using delta modulator. The minimum step size to avoid slope overload is (  b    )                                                                                                                      a. 1.0mV        b. 0.1mV                c.10.0mV                      d.0.01mV
3. For a 10 bit PCM system, the signal to Quantization noise ratio is 62 dB. If the number of bits are increased by 2, then the signal to Quantization noise ratio will be (  c      )                                                                                                                    a. Increased by 6 dB                                   b.  Decrease by 6 dB                                       c. Increased by 12 dB                                  d. Decrease by 12 dB
4. Write the condition to eliminate slope overload error in a Delta modulation system—————————
5. Write the condition to eliminate slope overload error in a Delta modulation system if the input is a single-tone signal—————————
6. For which value of A , A-law has linear transfer characteristics——————–.
7. For which value of µ , µ-law has linear transfer characteristics——————–.
8. In a PCM system if the step size is 5V , then the Quantization noise in dB is   (  d    )                                                                                                                                             a. -5 dB.          b. -3.18dB       c. -10dB                      d. 3.18dB.
9. Draw the characteristics of Mid-rise and Mid-tread type Quantizers ————–
10. The maximum slope of the signal ———————-
11. The sampling rate of the signal ————————–
12. The step size in a 8- bit pcm system if the input signal to PCM is oscillating between [+4V,-4V] is—————————–

UNIT-2

QUIZ 2

1. Entropy is a measure of ——————————– 3M.
2. The capacity of a band – limited AWGN channel in terms of kbps if the average received signal power to noise power spectral density is 1000 and the bandwidth is approximately infinite is (  a    )   [Hint: Shannon’s bound Cinfinity =  S/No]                                                                                                                        a.  1.44        b. 1.08                                c. 0.72                           d. 0.36
3. If Y= g(X) where g denotes a deterministic function, then the conditional entropy H(Y/X) is (  b ) 3M.                                                                                                           a. ≠ 1         b.  = 0                           c. = 1                           d. ≠ 0
4. A Source generates three symbols with probability of 0.25, 0.25, and 0.50 at a rate of 3000 symbols per second. Assuming the symbols are generated independently from the source, the most efficient source encoder would have average bit rate of ( b ) 4M.                                                                                             a. 6000 bits/sec                                                         b. 4500 bits/sec                                 c. 3000 bits/sec                                                         d. 1500 bit/sec.
5. A source generates four equi-probable symbols. If the source coding is adopted, the average length of the code for 100% efficiency is ( c )                       a. 6 bits / symbol                                                          b.   3 bits / symbol                           c.  2 bits / symbol                                                        d.  4 bits / symbol
6. Draw the channel diagram of Binary Erasure channel and write its channel matrix ………………………..
7. For a Binary Symmetric Channel the entropies of X & Y are if the conditional probability p=0.5, where X & Y are input & output random variables of BSC  (   d     )3M                                                                                                                          a. 1,0           b. 0,0               c. 0,1                           d. 1,1
8. Match the following   (  d    )                                                                                                       a. Lossless channel                                           1.  only one non-zero element in each row                                                                                                                                        b. Deterministic channel                                2. Only one non-zero element in each row and each column.                                                                                                   c. Noiseless channel                                           3. Only one Non-zero element in each column.                                                                                                                                d. for a noiseless channel                                  4. H(Y/X)=0 and H(X/Y)= 0. a. none of these                                                  b.   b-3,c-4,a-1,d-2                                    c. c-4,d-3,a-1,b-2                                             d.  b-1,c-2,a-3,d-4.
9. Given a Binary Symmetric Channel, the expression for Entropy is (pis conditional probability of error   ——————- 3M.

Digital Communications Unit-3 Quiz with Solutions

UNIT3

QUIZ3[CO3]

1. The number of Parity check bits in an (n, k) Linear Block codes are (    b      )      a.n                b. (n-k)                       c.  (n+k)                       d. k
2. The Hamming Weight of the following code words 10011101 & 00111100 is      (   c   ) 2M.                                                                                                                                       a. None of these      b. 4, 5              c.5, 4                           d.3,4
3. A cyclic code can be generated using———————— and A block can be generated using——————-.(   c   )                                  a.Generator matrix & Generator polynomial.                                                          b.Generator matrix & Generator matrix.                                                            c.Generator polynomial & Generator matrix.                                                            d.None of the above.
4. The rate of a Block code is the ratio of(    c     )                                                                a.Message length to Block length.                 b.Block length to message length.  c.Message weight to Block length.                 d.None of the mentioned.
5. The syndrome in LBC is calculated using , where Y represents received code word   (     a       ) 2M                                                                                                                      a. S= Y HT          b. S = YH                    c. S= YT H                  d. S= YT HT
6.  A non-Zero value of Syndrome in a Block code represents ( b    ) 2M.                  a.No error during transmission.     b.An error occurred during transmission.   c.Both a and  b                                         d.None of the above.
7. The transmitted code word(X) in an LBC can be obtained from received code word( Y) by using the equation (  a   ), where E represents error vector.              a. X= E + Y           b.  X = X.Y                  c. X= E.Y                    d. X= X/Y
8. The parity check matrix of a (6,3) block code if Generator matrix is G  3M. ——————-.
9. In the above question find the Code words corresponding to message vectors  and ——————-. Ans: , .
10. For the Q.8. Find the syndrome value when the received code word is 001111—-4MAns: syndrome value [0 0 1]
11. For a (7,4) cyclic code , the generator polynomial is given as find the codeword  for the data 1100       Non systematic codeword is—————- .Ans:  1011100              Systematic codeword is——————–.Ans: 1011100.

UNIT-4

QUIZ-4

1. The modulation technique that provides minimum probability of error is (  b   ). a. ASK                  b. PSK                   c. DPSK                        d.FSK
2. At a given probability of error, binary coherent FSK is inferior to binary coherent PSK by (  c  )                                                                                                         a. 6 dB                b. 2 dB           c.  3 dB           d.  0 dB             e. None of these.
3. If Eb, the energy per bit of a binary digital signal, is 10-5watt-sec and the one-sided power spectral density of the white noise, No= 10-6 W/Hz, then the output SNR of the matched filter is  (   d    )                                               a. 26 dB         b.  20 dB          c. 10 dB          d. 13 dB          e. None of these
4. In which system, bit stream is portioned into even and odd stream (   c   )  a. BPSK                  b.  MSK            c. QPSK                     d.  FSK
5. Optimum filter can be called as———when the input noise is white noise (  a   ) 2M.                                                                                                                        a. Matched filter   b.  High pass filter        c. Low pass filter      d. None of these
6. The probability of error of ASK is ————————————.
7. The probability of error of FSK is ————————————.
8. Write the expression for QPSK modulation —————————————-2M.
9. Draw the block diagram of DPSK system————————————.
10. A pulse g(t) = A cos(πt/2T) for 0 ≤ t ≤ T is transmitted over an AWGN channel with two sided noise power spectral density No/2 Watts/Hz. The impulse response of the matched filter is (  a     )                                                           a. A sin (πt/2T)                                                            b.   A rec (πt/2T)                           c. A rec (π(T-t)/2T)                                                    d. A sin (π(T-t)/2T)
11. If the probability of error function of a modulation scheme is Pe = (½) erfc(x) thenthe same Pe interms of Q-function is ( b   )                                             a. Q ( 31/2 * x)                    b. Q (21/2 * x)                c. Q(x)             d. none of these.
12. ## Analog Communications Important Questions unit 2 (FAQ)

UNIT 2:

1. What is meant by Carson’s rule? Problem on calculation of Bandwidth of FM signal using Carson’s rule.(imp)
2. Distinguish between NBFM and WBFM.(imp)
3. Problems on instantaneous phase and frequency.
4. What is the basic principle involved in Phase discriminator?
5. Define capture range and lock range of a PLL.
6. Problem on Armstrong method of generation of a WBFM signal?(imp)
7. Capture effect and threshold effects in FM (very very imp).
8. Problems on carrier swing, frequency deviation, BW, modulation index etc.
9. Phasor diagrams of NBFM and AM.
10. What is the need for limiter in FM receivers? (Very very imp).
11. Find the maximum Frequency deviation of Frequency Modulated signal given by  S(t) = 10 cos(1000000 *pi*t + 5 sin(2000*pi*t)).
12. A carrier signal 10 cos(8x 106πt) is modulated by a modulating signal               5 cos(30x 103πt)  then i. Find the Band width of Frequency Modulated signal assuming  kf  =15KHz.   ii.     Calculate Highest Frequency and lowest Frequency of FM signal.  iii. Find  Modulation index of FM signal.
13. Compare Frequency Modulation with Phase Modulation.

1. Explain the operation of balanced slope detector in detail.
2. Explain in detail about frequency spectrum of WBFM signal using Bessel functions.
3. write in detail about generation methods of FM signal
4. Direct method of generation
5. Indirect method of generation (Armstrong method).(very very imp)
6. What is ratio detector? Explain its working in detail with neat circuit diagram. Explain how ratio detector provides amplitude limiting?
7. What is amplitude limiter? Draw its circuit diagram explain its working. Why amplitude limiter is needed in FM receivers justify.(very very imp)
8. Compare and contrast foster seeley discriminator with ratio detector.
9. What is PLL? What are the applications of PLL? Explain the working of PLL with neat block diagram.(imp)
10. How audio frequency signal is demodulated by using PLL? Explain in detail.
11. Write about pre-emphasis and de-emphasis circuits in detail. Give the significance of pre-emphasis and de-emphasis.(imp)
12. In an FM system if the AF is 500 Hz and its amplitude is 2.4V with a frequency deviation of 4.8 KHz. If the AF voltage is increased to 7.2V then find the modified frequency deviation calculate BW in above two cases.
13. Design Armstrong FM generator for the generation of WBFM signal with frequency deviation=75 KHz and using the NB carrier as 100 KHz and second carrier as 10 MHz Find the suitable multiplying factors. Assume the message signal is defined in the range 100Hz-15 KHz.
14. Draw the block diagram of single-tone NBFM signal if message signal is.
15. Derive an expression for an FM signal with carrier frequency fc and a modulating signal Obtain an expression for its spectrum.
16. Why an FM system is preferred over an AM system?

Unit 2

Assignment 2

1. Explain the generation techniques of FM signal using Direct and Indirect methods in detail.
2. Explain the working of the following demodulator circuits of FM                        i. Balanced slope Detector for FM modulation.                                                            ii. Foster-Seeley discriminator.                                                                                         iii. Ratio-detector.
3. Explain the detection of FM signal using PLL.
4. Explain in detail about pre-emphasis and De-emphasis circuits in FM.

Unit 2

Assignment 2

1. Illustrate the working of PLL using a Block Diagram. Define capture range and Lock range in PLL.                                                                                                                 5M.
2. Sketch the circuit diagram of Ratio-detector and explain working of it in detail. 5M.
3. Sketch the frequency response curves & compare the working of pre-emphasis and De-emphasis circuits in FM communication System.

TUTORIAL TEST 2

Answer any three of the following

1. In an FM system if the AF is 500 Hz and its amplitude is 2.4V with a frequency deviation of 4.8 KHz. If the AF voltage is increased to 7.2V then find the modified frequency deviation calculate BW in above two cases.
2. Explain in detail about frequency spectrum of WBFM signal.
3. Draw the block diagram of single-tone NBFM signal if message signal is
4. Write any four differences between NBFM and WBFM.

## Basic Electronics Important Questions Unit 5 (FAQ)

UNIT-5

Data Acquisition systems: Study of transducer (LVDT, Strain gauge, Temperature, Force).

Photo Electric Devices and Industrial Devices: Photo diode, Photo Transistor, LED, LCD, SCR, UJT Construction and Characteristics only.

Display Systems:  Constructional details of C.R.O and Applications.

ASSIGNMENT- UNIT5

1. Explain with neat sketch, the working principle of LVDT.
2. Give the applications of CRO. Explain the Block diagram of Cathode ray tube in detail. 10M.
3. Write a short note on LED and LCD.

1. Distinguish between photodiode and LED.
2. Why is SCR known as negative resistance device?
3. What are the different types of transducers used for the measurement of temperature. Explain the principle of any of these.
4. Draw the symbol of a SCR and VI characteristics .explain its principle of operation.
5. What is meant by sensitivity in a CRO and explain the necessity of a saw tooth generation of a CRO.
6. What are the important characteristics of an LCD?
7. What is an LVDT? By means of a neat sketch explain how a LVDT is used in measurements.
8. Give the block diagram of a CRO, Explaining the importance of each block.
9. Explain about an instrumentation amplifier.
10. Write a note on UJT.
11. How are DIAC and TRIAC different from operational point of view.
12. What is a transducer?
13. List out the applications of a SCR.
14. Explain the principle involved in a strain gauge.
15. Draw the symbols of SCR, TRIAC, DIAC and UJT.

1. Explain the working of Cathode Ray Tube of CRO with neat block diagram in detail.
2. What are the applications of CRO?
3. Differentiate Photo Diode and Photo Transistor in detail in terms of operation and applications.
4. Differentiate LED and LCD in detail in terms of operation and applications.
5. Explain the working of SCR and draw the characteristics of it.
6. Explain the working of UJT and draw the characteristics of it.

ALL THE BEST

Prepared by         P.Lakshmi Prasanna

## Basic Electronics Important questions units 4 (FAQ)

Unit-4:  Operational Amplifiers – Introduction to OP Amp, characteristics and applications – Inverting and Non-inverting Amplifiers, Summer, Integrator, Differentiator, Instrumentation Amplifier.

Digital System: Basic Logic Gates, Half, Full Adder and Subtractors.

ASSIGNMENT- UNIT4

1. What are the four basic building blocks of Op-Amp explain each block in detail. 10M.
2. Write in detail about Instrumentation amplifier.
3. Design and realize Full Subtractor (Give the necessary expression and Truth table and Circuit diagram)

1. What are the ideal characteristics of OP-AMP?
2. What is an operational amplifier? Mention some of its applications.
3. A 5mV, 1 kHz sinusoidal signal is applied to the input of an OP-amp integrator for which R=100KΩ and C=1µF.Find the output voltage.
4. What are the different parameters of an OP-amp? Sketch the circuit of a summer using OP-amp 741to get Vo= -(-V1+2V2-3V3).
5. Write a note on basic logic gates.
6. Draw the truth table of an EX-OR gate.
7. State and prove De-Morgan’s theorems. Discuss the working of half adder and full adder and give their truth tables.
8. Write a note on universal gates.
9. Realize OR gate using NAND gates.
10. What is half Subtractor? Realize full Subtractor using using NAND gate only.
11. What is an op-amp? List the four building blocks of an op-amp.
12. Draw the schematic symbol of an op-amp in detail. Write the expression for output voltage of an op-amp?
13. What are the applications of op-amp?
14. What are the advantages of op-amp?
15. Why op-amp is named as op-amp?
16. What are universal gates and why those are called as universal gates?
17. Draw EX-OR and EX-NOR gates and give the truth tables of each gate.
18. Name some basic logic gates draw their symbols and give the corresponding truth tables.
19. Draw half adder and half Subtractor.

1. Draw and explain block diagram of op-amp in detail. Or what are the basic building blocks of an op-amp explain in detail.
4. Full Subtractor/ Half Subtractor.
5. Explain the operation of inverting and non-inverting amplifier circuits using op-amp and calculate gain of each circuit in closed loop configuration.
6. Define common mode rejection ratio (CMRR).a differential amplifier has a differential mode gain of 100 and common mode gain of 0.01 then find CMRR in dB?
7. Write in detail about instrumentation amplifier.
8. Explain the operation of the following circuits of op-amp in open loop configuration.    a. Non –inverting amplifier.        b.   Inverting amplifier  c.  Differential amplifier.
9. What are the characteristics of practical op-amp?
10. Define slew rate of op amp? Problem on calculation of Slew rate.
11. Explain how op-amp is used as  Summer and difference amplifier or Subtractor.

Prepared by                                                                                       P.Lakshmi Prasanna

## Basic Electronics Important Questions Unit 3 (FAQ)

UNIT – 3

Unit-3:  Feedback concepts: Properties of negative feedback amplifiers, Classification, Parameters. Oscillators: Barkhausen’s Criterion, LC Type and RC type oscillators and crystal oscillator. (Qualitative treatment only)

ASSIGNMENT- UNIT3

1. Draw the basic block diagram of feedback amplifier and explain each block in detail. 10M.
2. What is the effect of negative feedback on input and output impedances of a voltage series feedback amplifier? Give necessary expressions.
3. Write a short note about RC Phase Shift Oscillator.

1. What is meant by feedback?
2. What is tank circuit? How it is used in oscillators?
3. State Barkhausen’s criterion.
4. Differentiate positive feedback with negative feedback.
5. If open loop voltage gain of feedback amplifier is 200 and feedback factor is 1/5 then find
6. Gain with negative feedback.
7. BW with negative feedback if open loop BW is 100 KHz.
8. What are the advantages of negative feedback?
9. What is the effect of negative feedback on bandwidth?
10. Explain how gain stability is improved by negative feedback?
11. Draw block diagrams of voltage- series and current- shunt feedback topologies?
12. What are four topologies of feedback amplifiers?
13. What is positive feedback .Give the advantage of positive feedback?
14. Write the definition of oscillator?
15. Differentiate oscillators with the frequency of operation?
16. Draw under damped over damped and un-damped oscillatory signals.
17. .In the forward path of an oscillator, two amplifiers of equal gain are cascaded. If the feedback path transfer function is 1/81, find the gain of each amplifier.

1. What is the effect of negative feedback on input and output impedances in voltage-series feedback amplifier give necessary expressions?
2. Derive the general equation for LC oscillator circuits used in oscillators.
3. Distinguish between positive feedback and negative feedback in amplifiers. State the advantages of negative feedback in amplifiers.
4. Draw the circuit diagram of Hartley’s oscillator and explain its operation in detail. Derive the expression for frequency of oscillation.
5. Draw the circuit diagram of Colpitt’s oscillator and explain its operation in detail. Derive the expression for frequency of oscillation.
6. What is the effect of negative feedback on Bandwidth give explanation with necessary equations?
7. Write in detail about four topologies of feedback amplifiers and compare the topologies in terms of gain, BW, input impedance and output impedance.
8. Write the working operation of the following circuits and derive the expression of frequency of oscillation. i. RC-Phase shift oscillator. ii. Wein-bridge oscillator. iii. Crystal oscillator.
9. Draw a neat circuit diagram of an RC phase shift oscillator using BJT and explain its working principle
10. A Hartley oscillator is designed with L1=2mH, L2=20mH, and a variable capacitance. Determine the range of capacitance value, if the frequency of oscillation is varied between 950 kHz and 2050 kHz.

ALL THE BEST

Prepared by       P.Lakshmi Prasanna

## Basic Electronics Important Questions-Unit 2 (FAQ)

UNIT-2

ASSIGNMENT- UNIT2(CO2)

1. Draw the h-parameter equivalent model of transistor in CE configuration and define the four h- parameters.
2. Explain the construction of JFET (either n-channel or p-channel).
3. Explain the current components of a BJT in detail with a neat sketch.

1. Write the differences between JFET and BJT.
2. What are three possible configurations of BJT?
3. Define α, β and γ of a BJT write the relationship between them.
4. What are three possible regions of a transistor (write about cut-off, active and saturation regions).
5. What is base width modulation?
6. Define four h-parameters of transistor. And draw general h-parameter model of a BJT.
7. Define the following
8. Bandwidth of an amplifier.
9. Gain or amplification factor.
10. Compare CE, CB and CC transistors.( in terms of input resistance, o/p resistance, current gain, voltage gain, phase shift and applications).
11. What are the advantages of FET over BJT?
12. Why FET is more preferable than BJT?
13. How FET is known as uni polar device ? how do you compare FET with BJT?
14. Why FET is called as voltage controlled device?
15. What are the parameters of FET?
16. What are the three possible configurations of FET?
17. Give the relationship between gm , rd and µ.
18. Draw the equivalent circuit diagram of FET in CS configuration.
19. Why BJT is called as Current controlled device.
20. Draw transfer and output characteristics of FET.
21. Draw the symbols of NPN transistor,n channel FET and SCR.
22. If the emitter of a transistor is open will there be any collector current.

1. What is CB configuration? Draw the input and output characteristics of CB transistor. Explain in detail.
2. Define α and β of a transistor and derive the relationship between them.
3. Explain the current components of BJT in detail.
4. Explain how transistor is working as an amplifier?
5. Explain the working of CE amplifier with a neat circuit diagram. Derive expression for input resistance, and current gain using h parameter equivalent circuit.
6. Draw the hybrid equivalent circuit of an NPN BJT in CE configuration. Derive expressions for Av, Ai, Ri,
7. Calculate the values of Ic and Ib, for a transistor with α=.99,Ico=5µA,Ib=20µA.
8. Draw a simple inverter circuit and explain its operation.
9. Draw the h-parameter model of CE transistor and explain how h-parameters are calculated from CE characteristics.
10. Explain the construction and working of FET (either n-channel or p-channel).
11. Draw output and transfer characteristics of FET explain the working of /FET through them.
12. Derive the relationship between gm, rd and µ.
13. Write the comparisons between FET and BJT.
14. How FET is working as an amplifier?
15. Explain the working operation of NPN and PNP transistors.
16. Explain various operation regions of a transistor in detail.
17. What is CE configuration? Draw the input and output characteristics of CB transistor. Explain in detail.
18. What is CC configuration? Draw the input and output characteristics of CB transistor. Explain in detail.
19. What are the disadvantages of BJT? Why FET is preferred over BJT? Give the applications of FET.
20. Explain the working of JFET And explain the parameters of JFET.

ALL THE BEST

Prepared by      P.Lakshmi Prasanna

## Basic Electronics Important Questions -Unit-1 (FAQ)

Basic Electronics Important questions  –Unit-1

Note: Read the questions in the following order   i. Assignment questions ii. Class test  iii. Expected questions iv.  Tutorials For every unit.

Unit1:

ASSIGNMENT- UNIT 1

1.  Explain the working of Bridge rectifier in detail with a neat circuit diagram and derive the expression for ripple factor and efficiency. 10M.
2. Explain the working of PN-junction diode in detail in forward and reverse bias conditions. 10M.
3. A 230v, 60 Hz voltage is applied to the primary of a step down center tapped transformer of a FWR with turns ratio 5:1 is connected to a load resistance of 1 KΩ i. i. Determine voltage across the load. ii. DC current through the load. If there is a resistance of 100Ω for the transformer secondary and diode forward Resistance is given as 10Ω.

1. Write the expression of diode current equation and explain each term in detail.
2. Define cut in or threshold voltage of a diode. Give the values of Vof Si and Ge diode.
3. Write the differences between Extrinsic and Intrinsic semiconductors.
4. What are P-type and N-type semiconductors?
5. Write in detail about Drift and Diffusion currents.
6. Draw the Energy Band Diagrams of an insulator, semiconductor, Conductor.
7. Write the differences between insulators, conductors and semi conductors.
8. Define the following   a. Mobility b. Conductivity  c. Mass Action law. d.Fermi level in semi conductors.
9. Draw the diagrams for Fermi-level in Intrinsic, N-type and P-type semi conductors and write the formula for EF in the above two cases.
10. Define Hall Effect and write the uses or applications of Hall Effect.
11. What properties of semi conductor are defined from Hall Effect?
12. What is a diode and write the applications of Diode.
13. Draw the VI-Characteristics of a diode. And calculate Static and Dynamic resistances from the characteristics.
14. Write about diffusion and Transition capacitances of a diode.
15. Define avalanche breakdown and zener breakdown.
16. What is avalanche effect and zener effect?
17. What is a rectifier? Differentiate between Half Wave Rectifier and Full Wave Rectifier.
18. Draw the equivalent circuit of practical Diode under forward bias and Reverse Bias.
19. Draw the equivalent circuit of ideal Diode under forward bias and Reverse Bias.
20. Define Peak Inverse Voltage (PIV) of a diode in a rectifier circuit. Write the PIV values in HWR, FWR and Bridge Rectifier.
21. Define the following i. Ripple factor       ii. Regulation or Percentage of Regulation. iii. From factor and peak factor. iv. Efficiency of a rectifier  v. RMS value and average value of voltage or current wave in half wave rectifier.
22. Write the applications of Zener Diode.
23. Explain how Zener diode works as a regulator.
24. What is the concentration of holes in Si crystals having donor concentration of 1.4 x 1024/m3 when the intrinsic carrier concentration is 1.4 x 1018/m3 ? Find the ratio of electron to hole concentration.
25. Problems on motilities of n-type and p-type semiconductors.
26. An n-type Ge crystal has a current density of 100A/m2. The crystal has a resistivity of 0.5 Ω-m and electron mobility of 0.4 m2/V-s. Calculate the drift velocity and the time taken by the electron to travel 10 micrometer in the crystal. Assume q= 1.6 x 10-19
27. Problems on Fermi levels.
28. Problems on diode current equation in forward bias and reverse bias.
29. Write the advantages of full wave and bridge rectifiers over half wave rectifier.

1. Define Hall Effect. Derive the expression for Hall voltage and hall coefficient and explain the uses of Hall Effect.
2. Derive the expression for transition and diffusion capacitances of a diode.
3. Explain the working of Zener Diode as a regulator.
4. Derive the expression for ripple factor and efficiency of a Half Wave rectifier and full wave rectifier.
5. Derive the expression for ripple factor and efficiency of a bridge rectifier.
6. Compare half wave rectifier, FWR and Bridge rectifier in terms of (ripple factor, percentage of regulation, efficiency, PIV, from factor and peak factor etc…… read the comparison table in text book).
7. How will you find the dynamic and static resistance of the diode using a graph?
8. What is an ideal diode? How can it be represented as a switch? Draw the equivalent circuit and its characteristics.
9. Draw the VI-Characteristics of a PN junction diode in forward and reverse biased conditions. Define forward resistance and reverse resistances and explain how they can be obtained from the characteristics.
10. Draw the circuit diagram of a half wave rectifier and explain its operation with wave forms.
11. Draw the circuit diagram of bridge rectifier and explain its operation with wave forms.
12. Draw the circuit diagram of a full wave rectifier and explain its operation with wave forms. What is its advantage over half wave rectifier?
13. What is static resistance of the diode? How will you find the dynamic resistance?
14. Explain the zener and avalanche thermal breakdown mechanisms. What will be their thermal coefficients?
15. How is a PN junction formed? Draw the circuit diagram of PN-Junction diode in forward bias and reverse bias. Explain its operation and give VI-characteristics.
16. What is a rectifier? Draw the circuit diagram for bridge rectifier with LC-filter and explain its operation.
17. Explain bridge wave rectifier with circuit diagram and output wave forms. Find      i. RMS value of current.   ii. Ripple factor.  iii. TUF   iv. Efficiency   v. Peak factor.
18. Explain avalanche breakdown and zener breakdown in PN diode.
19. Derive the expression for ripple factor of a FWR (or HWR/ Bridge) with shunt capacitance filter.
20. Derive the expression for ripple factor of a FWR (or HWR/ Bridge) with series inductance filter.
21. Derive the expression for ripple factor of a FWR (or HWR/ bridge) with LC π section filter.
22. Derive an expression for current in a diode.
23. Compare drift and diffusion currents.

Tutorial -1 Questions

1. A Full Wave Rectifier has a Secondary Voltage of 230V from one-end of the transformer to ground. then calculate i. DC load Current. ii. RMS value of output current. If diode has a resistance of 10Ω and the resistance of secondary winding is negligible. Given RL=5KΩ.
2. Find the conductivity of P-type semi conductor, if the concentration of holes is 4.2X1022atoms/m3 and mobility of holes is 1800 Cm2/V.
3. Write the expression for Hall voltage and find Hall voltage if the Magnetic field strength of 1000 Wb/m2 where the current flowing through the semi conducting material is 9A. Width of semi conducting material is 2m with resistivity of 100 Mhos-m. Also find the Hall coefficient?
1. Write a short note on P-type and N-type semi conductors.

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Prepared by                                                                                       P.Lakshmi Prasanna

## Digital Modulation schemes Viva Questions

2. Draw the waveforms of ASK scheme.
3. Draw the Phasor diagrams of ASK.
4. Write the equation of ASK wave.
5. What are the applications of ASK?
7. Write the expression for Probability of error of ASK.
8. What is the BW of ASK?
9. Draw the signal constellation diagram of ASK.
10. Draw the block diagram of ASK generator. Explain its working.
11. Draw the block diagram of coherent ASK demodulator. Explain its working.
12. Draw the block diagram of non-coherent ASK demodulator. Explain its working.
13. How ASK is different from AM?
14. If bit rate is 10µsec then calculate the band width of ASK.
15. Which is the efficient modulation scheme among ASK and PSK give the reason.
16. Write the relation between complementary error function and Q-Function.
17. Write the Pe of ASK in terms of Q function.
18. What is meant by Signal space diagram?
19. A source generates three symbols with probability 0.25,0.25 and 0.5 at a rate of 3000 symbols/sec Assuming the symbols are generated independently from the source the most efficient source encoder would have average bit rate of——————————.

FSK Generation & Detection:

1. Define FSK. Write the practical applications of FSK.
2. Draw the waveforms of FSK scheme.
3. Draw the Phasor diagrams of FSK.
4. Write the equation of FSK wave.
6. Write the expression for Probability of error of FSK.
7. What is the BW of FSK?
8. List some applications of FSK.
9. Draw the block diagram of FSK generator and explain its working.
10. Draw the block diagram of coherent FSK demodulator and explain its working.
11. Draw the block diagram of non-coherent FSK demodulator and explain its working.
12. Show that FSK is inferior to PSK by 3dB for a given probability of error.
13. Define digital modulation schemes.
14. Identify the differences between Pass band and Base band Communication.
15. What is a matched filter?
16. What are the properties of matched filter?
17. What is MSK? What is the need for Minimum Shift Keying?
18. For the given 8 bit data 10111010 draw the FSK output waveform.
19. Draw the constellation diagram of FSK.
20. What will happen if the same frequency is used for both the carriers?
21. Draw FM signal and FSK signal differentiate those two signals.
22. What are the applications of FM?
23. How FSK is different from FM?
24. Write the probability of error expression of FSK in-terms of Q function.
25. Write the relation between complementary error function and Q-Function.
26. Among FSK and PSK which is the most efficient scheme and why?

PSK Generation & Detection:

1. Define PSK. Write the practical applications of PSK.
2. Draw the waveforms of PSK scheme.
3. Draw the signal space diagram of PSK.
4. Write the equation of PSK wave.
5. What are the applications of PSK?
7. Write the expression for Probability of error of PSK in terms of erfc()
8. Write the expression for Probability of error of PSK in terms Q().
9. Write the difference between erf(x) and erfc(x)..
10. What is the BW of PSK?
11. What are antipodal signals?
12. Give the equation for average probability of symbol error for coherent binary PSK.
13. Explain how QPSK differs from PSK in terms of transmission bandwidth and bit information it carries.
14. What are the advantages of M-ary modulation scheme?
15. Draw the constellation diagram for QPSK.
16. Compare FSK and PSK.
17. What do we infer from constellation diagrams of various modulation schemes?
18. Draw the block diagram of PSK generator. Explain its working.
19. Draw the block diagram of coherent PSK detector. Explain its working.
20. How non coherent PSK is advantageous over coherent PSK?
21. Other name of Non-coherent PSK is———–.
22. Write the expression for a Gaussian function———————.

DPSK Generation & Detection:

1. Define DPSK.
2. Draw the waveforms of DPSK scheme.
3. Write the equation of DPSK.
4. What are the applications of DPSK?
6. Write the expression for Probability of error of DPSK.
7. What is the BW of DPSK?
8. What are the applications of DPSK?
9. Draw the DPSK system and explain its working.
10. If the input sequence to a DPSK modulator is 10011100 write the following sequences, Deferentially encoded sequence if previous bit is 0 And the phase of the encoded sequence.
11. The capacity of a band limited AWGN channel in terms of KBPS if the average received signal to noise power spectral density is 1000 and the BW is approximately infinite is…………..
12. For error free channel conditional probability is ————-.
13. The modulation technique that provides minimum probability of error is———-.

QPSK Generation & Detection:

1. Define QPSK.
2. Draw the waveforms of QPSK scheme.
3. Draw the Phasor diagrams of QPSK.
4. Write the equation of QPSK wave.
5. What are the applications of QPSK?
7. Write the expression for Probability of error of QPSK.
8. Draw the block diagram of QPSK modulator. Explain its working.
9. Draw the block diagram of coherent QPSK de modulator. Explain its working.
10. Write the table for four di-bits with phases used in a QPSK modulation scheme.
11. Write the equation of QPSK wave.
12. What is the BW of QPSK?
13. What are the applications of QPSK?
14. Draw the constellation diagram for QPSK.
15. In Minimum Shift Keying the relation between the signal frequencies and bit rate are————.
16. A pulse for is passed through a matched filter then the impulse response of matched filter is—————————.
17. A lossless channel means—————–.
18. A distortion less channel means————————-.
19. Write the channel matrix for a Binary symmetric channel——————–.

Losses in fibre optics:

1. Define Transmission loss of Optical fibre?
2. What are various losses in fibre optics?
3. What are step index graded index optical fibers?

Data Formats:

1. Compare NRZ-I and NRZ- L.
2. What is the use of data formatting?
3. Compare NRZ and biphase encoding.
4. What is the relationship between quantization levels and number of bits in a code word?
5. Give the advantages of Manchester encoding.
6. Assume a data stream is made of ten 0s. Encode this stream using the following encoding schemes.
7. How much change can you find for each scheme? a)NRZ b)RZ c)Bi phase
1. List out the merits & demerits of each data formats.
2. Represent the given data 11010100 in Manchester encoding and NRZ –M scheme.

## Delta Modulation and Demodulation Viva Questions

Delta Modulation & Demodulation:

1. What is Delta Modulation?
2. A message signal m(t) has a BW of 1KHz and exhibits a maximum rate of change of change of 2 Volts/sec the signal is sampled at a sampling frequency of 20 KHz and Quantized using a delta modulator the minimum step size to avoid slope overload is———-
3. Which type of Quantization is used in DM?
4. What are two types of quantization errors?
5. What is granular noise?
6. What is slope overload distortion?
7. Draw the block diagram of Delta Modulation system.
9. What happens to the output signal if the variation of the message signal is
• greater than the step size
• less than the step size
1. What is the advantage of delta modulation over PCM?
2. Compare DPCM, PCM& Delta modulation.
3. How to reduce the quantization noise that occurs in DM?
4. A band pass signal has a spectral range that extends from 20 to 82 KHz. Find the acceptable sampling frequency.
1. Find the Fourier series expansion of an Impulse train.
2. Mention the applications of DM.
3. Write the condition to eliminate Slope over load distortion in Delta Modulation for a single tone message signal.
4. Write the condition to eliminate Slope over load distortion in Delta Modulation for some arbitrary signal.
5. We chose oversampling in DM system. True or False?
6. How DPCM is different from DM?
7. Draw the waveforms of DM demodulation and Demodulation.
8. Differentiate Coherent and Non coherent modulation schemes.
9. Explain the working DM system.
10. Draw the Wave forms and explain two distortions in DM system.

## Pulse Code Modulation Viva Questions

Pulse Code Modulation:

1. What is PCM? Does PCM come under Digital Modulation technique?
2. What are the applications of PCM?
3. What is the need for Regenerative repeaters in PCM?
4. Draw the block diagram of PCM system.
5. Define µ-law and A-law. And draw the characteristics of two laws.
6. What is meant by Quantization?
7. Differentiate Uniform and Non uniform Quantization techniques.
8. What is meant by companding in PCM?
10. What is the difference between ADC & PCM?
13. What is slope overload distortion?
14. Draw the waveforms of PCM modulation and demodulation.
15. State sampling theorem.
16. What is aliasing?
17. Give the expression for aliasing error and the bound for aliasing error.
18. What is quantization?
19. What are the various steps involved in A/D conversion.
20. Define step size.
21. What is the importance of regenerative repeater?
22. List out the three basic functions of regenerative repeater.
23. What is companding?
24. Write the mean square quantization error if the step size is S.
25. What is a mid tread Quantizer?
26. What is a mid rise Quantizer?
27. What do you mean by quantizing process?
28. What will happen when sampling rate is greater than Nyquist rate?
29. What will happen when sampling rate is less than Nyquist rate?
30. Find the A/D Converter output for input DC voltage of 3.6V.
31. In digital telephony, (a) what kind of modulation is used? (b)Give the typical sampling rate, output data rate and speech signal Bandwidth.
32. Mention some applications of PCM.
33. What is the function of Sample and Hold circuit?
34. Write the expression for SNR in decibels of a PCM system.
35. For a DAC the required resolution is 25mv and the total input is 5V. the number of bits required would be——————————————.

## Digital Communications Quiz unit-3

Digital Communications Unit-3 Quiz with Solutions

UNIT3

QUIZ3[CO3]

1. The number of Parity check bits in an (n, k) Linear Block codes are (    b      )      a.n                b. (n-k)                       c.  (n+k)                       d. k
2. The Hamming Weight of the following code words 10011101 & 00111100 is      (   c   ) 2M.                                                                                                                                       a. None of these      b. 4, 5              c.5, 4                           d.3,4
3. A cyclic code can be generated using———————— and A block can be generated using——————-.(   c   )                                  a.Generator matrix & Generator polynomial.                                                          b.Generator matrix & Generator matrix.                                                            c.Generator polynomial & Generator matrix.                                                            d.None of the above.
4. The rate of a Block code is the ratio of(    c     )                                                                a.Message length to Block length.                 b.Block length to message length.  c.Message weight to Block length.                 d.None of the mentioned.
5. The syndrome in LBC is calculated using , where Y represents received code word   (     a       ) 2M                                                                                                                      a. S= Y HT          b. S = YH                    c. S= YT H                  d. S= YT HT
6.  A non-Zero value of Syndrome in a Block code represents ( b    ) 2M.                  a.No error during transmission.     b.An error occurred during transmission.   c.Both a and  b                                         d.None of the above.
7. The transmitted code word(X) in an LBC can be obtained from received code word( Y) by using the equation (  a   ), where E represents error vector.              a. X= E + Y           b.  X = X.Y                  c. X= E.Y                    d. X= X/Y
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