QPSK equation, wave forms and Signal space diagram

QPSK equation:-

The meaning of QPSK is  that the carrier signal takes on different phases Π/4, 3Π/4, 5Π/4 and 7Π/4 based on incoming di-bit combination  or symbol.

\large S_{QPSK}(t)= \sqrt{\frac{2E_{s}}{T_{s}}}cos(2\pi f_{c}t +(2i-1)\frac{\pi}{4}), 0\leq t\leq T_{s}

                    = 0, elsewhere, where  i =  1,2,3,4.

Eb and Tb are the bit energy and bit-interval , Es and Ts are the energy per symbol  and symbol duration. Ts = 2 Tb

The carrier frequency fc = nc /Ts. where nc is a fixed integer.

each possible value of phase corresponds to a unique di-bit. then the foregoing phase values to represent the gray encoded set of di-bits 11,01,10 and 00, where only a single bit is changed from one di-bit to the next.

QPSK equation can be represented in another format as follows

\large S_{QPSK}(t) = \sqrt{\frac{2E_{s}}{T_{s}}}cos (2\pi f_{c}t+(2i+1)\frac{\pi }{4} ), 0\leq t\leq T_{s}

                        = 0, elsewhere   ,where i=0,1,2,3.

The above two equations are same, there is a change in i values. alternately the equation can be represented as follows.

S_{QPSK}(t)= \sqrt{\frac{2E_{s}}{T_{s}}}cos (2i-1)\frac{\pi }{4}cos2\pi f_{c}t - \sqrt{\frac{2E_{s}}{T_{s}}}sin (2i-1)\frac{\pi }{4}sin2\pi f_{c}twhere i= 1,2,3,4.

The above equation can be expanded cos(A+B). There are two orthogonal functions Φ1(t) and Φ2(t) where 

\Phi _{1}(t)=\sqrt{\frac{2}{T_{s}}}cos 2\pi f_{c}t, 0\leq t\leq T_{s}, \Phi _{2}(t)=\sqrt{\frac{2}{T_{s}}}sin 2\pi f_{c}t, 0\leq t\leq T_{s}

S_{QPSK}(t)=\sqrt{E_{s}}cos(2i-1)\frac{\pi }{4} * \Phi _{1}(t) - \sqrt{E_{s}}sin(2i-1)\frac{\pi }{4} * \Phi _{2}(t)

Let    b_{o}(t)= \sqrt{E_{s}}cos(2i-1)\frac{\pi }{4}     and   b_{e}(t)= -\sqrt{E_{s}}sin(2i-1)\frac{\pi }{4}

then the resultant equation is:     S_{QPSK}(t)= b_{o}(t) * \Phi _{1}(t) + b_{e}(t) * \Phi _{2}(t).

 

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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.

 

Short Answer Questions:

  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.

Long Answer Questions:

  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.

 

 

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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.

Short Answer Questions:

  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.

Long Answer Questions:

  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 Communications Teaching notes

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Basic Electronics Lab Viva Questions

Experiment wise viva questions Basic Electronics Lab

PN-Junction Diode:

  1. What is a diode?
  2. What are the applications of diode?
  3. Draw the symbol of PN junction diode and mark anode and cathode.
  4. Define threshold voltage or cut in voltage of a diode.
  5. define dynamic and static resistances of a diode.
  6. Cut-in voltage of Si diode is…………………
  7. Cut-in voltage of Ge diode is…………………
  8. Draw the VI characteristics of PN junction diode.
  9. What is forward bias of a junction diode? Explain with circuit diagram.
  10. What is reverse bias of a junction diode? Explain with circuit diagram.
  11. Define space charge or Depleted region of a diode?
  12. Explain the working operation of a junction diode in forward and reverse bias.
  13. p type material means………….. Give some examples of N-type materials
  14. n type material means…………Give some examples of P-type materials
  15. Ideal diode acts as short circuit under forward bias. Or draw the equivalent circuit of ideal diode in forward bias.
  16. Ideal diode acts as open circuit under reverse bias. Or draw the equivalent circuit of ideal diode in reverse bias.
  17. Draw the equivalent circuit of practical diode in forward bias and reverse bias.
  18. What are the differences between avalanche and Zener break down.
  19. What are intrinsic and extrinsic impurities?
  20. Differentiate a conductor, semiconductor and dielectric material.
  21. Write the diode current equation.

 Zener Diode:

  1. What is Zener diode? Define how it is different from ordinary PN diode.
  2. What are the applications of Zener diode?
  3. Draw the symbol of Zener diode and mark anode and cathode.
  4. Define Zener breakdown.
  5. What is the Zener breakdown voltage value———–.
  6. How Zener diode is acting as a voltage regulator?
  7. What is the cut-in voltage of a Zener diode————.
  8. Draw the equivalent circuit of Zener diode?
  9. Zener diode operates in reverse bias? Why?
  10. Explain avalanche multiplication in detail.
  11. Explain Zener multiplication in detail.
  12. Give two differences between avalanche and Zener multiplication.

Half Wave rectifier and Full wave Rectifier (same questions are valid for FWR)

  1. What is a rectifier? How diode is used as a rectifier?
  2. Define ripple factor?
  3. What is the need for filter at the output of a rectifier?
  4. What is percentage of regulation?
  5. Give the ripple factor values for HWR and FWR (read comparison table between HWR and FWR).
  6. What is the efficiency of HWR and FWR? Give values.
  7. What are the advantages of FWR over HWR?
  8. What are the disadvantages of HWR?
  9. What are the drawbacks of FWR?
  10. Define PIV of a diode.
  11. PIV of HWR and FWR are………..
  12. why we need rectifiers?
  13. where we use rectifiers ?
  14. what are the differences between rectifier and converter?

CE/CB characteristics:

  1. Draw the symbol of transistor.
  2. Draw pnp and npn transistor symbols.
  3. What are three configurations of a BJT?
  4. Draw the circuits of CE, CB and CC configurations.
  5. What is CE or Grounded Emitter configuration?
  6. What is CB or Grounded Base configuration?
  7. What is CC or Grounded Collector configuration?
  8. What are input and output characteristics of BJT?
  9. Draw input and output characteristics of CE configuration.
  10. Draw input and output characteristics of CB configuration.
  11. What are the applications of CE and CB transistors?
  12. Comparison table of CE, CB and CC configurations in terms of input resistance, output resistance, voltage gain, current gain and applications.
  13. What are the three terminals of a transistor?
  14. Define doping levels of emitter, base and collector.
  15. Define early effect in CB transistor.
  16. The majority carriers in pnp transistor are………..
  17. The majority carriers in npn transistor are………..
  18. Why BJT is called as bipolar device?
  19. Is BJT a uni polar or bipolar device?
  20. What are the applications of transistors?
  21. what is the phase difference between input and output waveforms of CE transistor( ans: 180o)
  22. What is the phase difference between input and output waveforms of CB transistor ( ans: 0o or 360o).
  23. Why NPN transistor is preferred over PNP transistor?
  24. Why CE is preferred over other combinations in voltage amplifiers?
  25. Define saturation, cutoff, active regions of a transistor?
  26. What is cutoff region of operation of a transistor?
  27. Read about comparison tables of Si, Ge transistors for active cutoff and cutin and saturation voltages.

JFET:

  1. What is FET or JFET?
  2. What are the differences between BJT and FET?
  3. Why BJT is called as Current controlled device?
  4. Why FET is called as Voltage controlled device?
  5. Draw the symbol of FET?
  6. Symbols of N-channel and p channel FETs.
  7. Differences between N- channel and P- channel FET’s?
  8. Draw the input or output characteristics of JFET?
  9. What are the meanings of source drain and gate?
  10. What are the applications of FET?
  11. What are the advantages of FET over BJT?
  12. Draw h-parameter model of a BJT in CE/CB configurations?
  13. Define pinchoff voltage of a FET?
  14. Explain about linear saturation and breakdown regions of CE/CB output characteristics?
  15. Explain about linear saturation and breakdown regions from drain or output characteristics of JFET
  16. Define 4 h-parameters of BJT in CE configuration?
  17. Draw the equivalent circuit of FET?
  18. define µ, g , rd in FET? what is the relation between those three parameters?
  19. define trans conductance and drain resistance of FET?
  20. The input resistance of a JFET is very high in Mega ohms.
  21. Working of JFET.
  22. Applications of JFET.

 

Operational Amplifier:

 

  1. What is Operational Amplifier?
  2. What are the ideal characteristics of Op-amp?
  3. What are the applications of op-amp?
  4. What is inverting amplifier?
  5. What is non inverting amplifier?
  6. What is meant by open loop and closed loop op-amp?
  7. Identify the feedback resistor in inverting and non inverting amplifiers (ans:Rf).
  8. What are the advantages of op-amp over feedback amplifiers?
  9. Define slew rate?
  10. Draw circuits of integrator and differentiator using op-amp
  11. Draw adder and subtractor circuits using op-amp.
  12. What is virtual ground in op-amp circuits?
  13. What is open loop gain of an ideal op amp?

Oscillators:

RC Phase Shift Oscillator:

  1. Mention the two conditions required for oscillations in RC phase shift oscillator?
  2. Give the formula for frequency of oscillations in RC phase shift oscillator?
  3. The phase produced by a single RC network is RC phase shift oscillator?
  4. RC phase shift oscillator uses positive feedback or negative feedback?
  5. The phase produced by basic amplifier circuit in RC phase shift oscillator is?
  6. What is the difference between damped oscillations and un damped oscillations?
  7. What are the applications of RC phase shift oscillator?
  8. How many resistors and capacitors are used in RC phase shift feedback network?
  9. How the Barkhausen’s criterion is satisfied in RC phase shift oscillator
  10. Mention the basic reason for any oscillations?
  11. What is meant by Barkhausen’s criterion?
  12. Audio frequency range is————
  13. RC phase shift oscillator is ——–
  14. Oscillator is a circuit operates on internal input power supply yes or no?
  15. Define an oscillator?
  16. Oscillator did not take any external input yes or no?
  17. Type of feedback used in oscillators is——-
  18. Radio frequency range is———–
  19. Show that single RC section provides a phase shift of 60 degrees.
  20. Positive feedback causes instability yes or no?
  21. In oscillators loop gain must be————–
  22. In oscillators the overall phase shift produced by the circuit is————
  23. Feedback gain 𝛽 must be less than———–

 COLPITTS AND HARTLEY’S OSCILLATORS:

  1. What are the advantages of hartley’s and colpitts oscillators over RC phase shift oscillator?
  2. Applications of Colpitts and Hartleys oscillators are—–.
  3. Colpitts oscr uses ———- in its feedback network.
  4. Hartleys oscr uses ———–in its feedback network.
  5. Define mutual inductance—–
  6. colpitts and hartleys ocsillators are used at ———— frequencies.
  7. Give the formula for frequency of oscillations in Colpitts oscillator.
  8. Give the formula for frequency of oscillations in Hartley’s oscillator?

SINGLE STAGE CE AMPLIFIER:

  1. What is the phase difference between input and output waveforms of a CE amplifier?
  2. What type of biasing is used in the given circuit?
  3. What is the effect of emitter bypass capacitor on frequency response of a CE amplifier?
  4. What is the effect or importance of coupling capacitor?
  5. Why source resistance Rs is used in the input side?
  6. What are the different regions of operation of a BJT?
  7. The phase difference of input and output in CB amplifier?
  8. CE amplifier is voltage or current amplifier?
  9. Draw the equivalent h-parameter model of a CE amplifier?
  10. Why NPN transistor is preferred over PNP transistor?
  11. What is the effect of bypass capacitor over stability of the CE amplifier?
  12. The CE amplifier is in voltage divider bias or in fixed bias configuration?
  13. The values of hfe,hie,hoe and hre in CE configuration are—————-.
  14. hfe,hie,hoe and hre are called as——————–.
  15. What do you mean by loading effect?
  16. What are the practical applications of single stage CE amplifier?
  17. How do you know the amplifier is single stage CE amplifier?
  18. Why this circuit is called RC coupled amplifier?
  19. What is the operating point in CE amplifier from the design specifications?
  20. Quiescent conditions means——–
  21. D.C conditions are for———
  22. What is the relationship between collector current and base current?
  23. Does β and hfe are one and the same?
  24. Why coupling capacitor Cb is connected in reverse (-,+) at the input side and Cc is connected in forward(+,-) at the output side?
  25. How do u know a transistor is working in cut off region?
  26. Write VBE(active),VBE(sat),VBE(cutoff) values of a Si and Ge transistors
  27. Transistor meaning is———
  28. Define frequency response of a CE amplifier?
  29. Define voltage gain of a CE amplifier?
  30. Units of gain as a ratio are———-
  31. Units of gain in logarithim is———
  32. Magnitude response and frequency response are one and the same say yes or no?
  33. Define bandwidth?
  34. What are 3 dB frequencies?
  35. Define cutoff frequencies?
  36. BW is approximately equal to fH justify?
  37. Gain is constant in————-
  38. Semi logarithmic graph is linear or non linear graph?
  39. Stability factor is a function of—–
  40. In the circuit R1 and R2 are used for——–
  41. The feedback type that Re and Ce introduces in the circuit is———–(Ans: negative feedback).
  42. Negative feedback increases stability yes or no(Ans:yes).
  43. CB amplifier provides more band width than CE amplifier justify?

 

Note: Read advantages and disadvantages and applications of every experiment.

 ALL THE BEST 

 Prepared by   P.Lakshmi Prasanna