Code: DC-02                                                  Subject: FUNDAMENTALS OF ELECTRONICS

Time: 3 Hours                                                                                                     Max. Marks: 100

NOTE: There are 11 Questions in all.

· Question 1 is compulsory and carries 16 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Answer any THREE Questions each from Part I and Part II. Each of these questions carries 14 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1       Choose the correct or best alternative in the following:                                           (2x8)

a. An example of a resistor with negative temperature coefficient is

(A) The metal-film resistor.                  (B) The wire wound resistor.

(C) The carbon-film resistor.                (D) a MOS simulating a resistor.

             b.   For a BJT in its saturation region, the collector-to-base and the base-to-emitter junctions are

(A) zero biased.                                 

(B) reverse biased and forward biased, respectively.

(C) forward biased & reverse biased respectively.                                                           

(D) forward biased.

             c.   For the standard TTL-IC family, the typical value of propagation delay is

(A) 7 ns.                                             (B)  10 ns.

(C)  14 ns.                                           (D)  5 ns.

             d.   The decimal number corresponding to the third cell in the second row of a Karnaugh map for four variables is

(A)  8.                                                 (B)  15.

(C)  13.                                               (D)  10.

             e.   One of the most widely used LC oscillators is

(A) the phase-shift oscillator.                (B)  the Hartley oscillator.

(C) the Colpitts oscillator.                    (D)  the Clap oscillator.

f. In a Hartley oscillator, the feed back voltage is developed by

(A) the capacitive voltage divider.        (B) the collector resistor.

(C) the inductive voltage divider.          (D) the feed back capacitor.

             g.   MOS logic is mainly used for

(A) MSI ICs.                                      (B)  SSI ICs.

(C) VLSI ICs.                                     (D)  ULSI ICs.

             h.   The main advantage of a CC configuration is its 

(A) High output impedance                 (B)  Low input impedance

(C)  High input impedance                   (D)  High current gain

PART I

Answer any THREE Questions. Each question carries 14 marks.

Q.2     a.   What is covalent bonding?  Illustrate the atomic structure of Germanium and Silicon.  Comment on the covalent bonding of Si atom.                (6)

             b.   Distinguish between intrinsic and extrinsic materials.  Draw the energy band diagram that shows the conduction and valance bonds of an insulator, a semiconductor, and a conductor.               (8)

Q.3     a.   Explain the operation of a PN junction under zero bias and forward bias conditions.            (10)

b. What is the equation that describes the characteristic of a semiconductor diode?  Draw the forward characteristic of a silicon diode and briefly explain its features.                                            (4)

Q.4     a.   What is a junction transistor?  Draw the circuit diagram of an npn transistor in CB configuration and describe its driving point characteristics for a silicon transistor in the circuit.                                       (10)

b.   Allow 0.7 V for the  drop in figure 1 and calculate the dc collector-base voltage .                                                                      (4)

Q.5     a.  Define the logic operations indicated below:

(i)  OR,        (ii)  AND,        (iii)  NOT                                                                   

                   Explain how the above operations can be realised using only NAND gates.         (8)

b. What is Boolean algebra?  Using the theorems of Boolean algebra and its postulates verify the following :

(i)  X + X = X,       (ii)  X + 1 = 1,      (iii) X + XY = X

Mention the theorems/postulates used in the verification at each step.                  (6)

  Q.6     a.   How are digital ICs classified?  Based on the above, indicate the different IC packages available commercially with their compositions.   (8)

             b.   Why do MOS devices have a large propagation delay time?  What is CMOS logic?  Draw the circuit of a two-input CMOS NAND gate and explain its operation.                                                    (6)

PART II

Answer any THREE Questions. Each question carries 14 marks.

Q.7     a.   State Thevenin’s theorem.  For the circuit shown in figure 2, determine the Thevenin’s equivalent voltage  and resistance  for the load .                                                                   (7)

             b.   What is a ‘Varactor’?  Draw a diagram showing its structure and give its equivalent circuit.  Briefly explain its features.  When a varactor is connected in parallel with an inductor, what is the resultant circuit called?                                                           (7)

Q.8     a.   What is an FET?  Make a comparison between a FET and a BJT.  Give the schematic symbol for an n-channel depletion type MOSFET.        (8)

             b.   Explain briefly the drain and transfer characteristics for an n-channel depletion type MOSFET.                                                                   (6)

Q.9     a.   What is the advantage of using a JFET as a switch?  With neat illustrations, explain how the JFET can be used as a series switch and a shunt switch.                                                          (8)

b.   What are the different ways of connecting the feedback signal in an amplifier?  Give the scheme for each one of them.                                               (6)

Q.10           a.                                                        How are digital circuits divided broadly?  Define each one of the categories.                                                                                                         (3)

     b.   Prepare the truth table for the Karnaugh map shown in figure 3.                          (3)                      

c.   Minimize the four-variable logic function using Karnaugh map.

(8)

Q.11           a.                                                        What is an operational amplifier?  What does it contain as the main building block?  Mention its typical applications.                                                 (5)

b.   Draw the circuit of an OPAMP, in the inverting mode, to sum three input voltages  and .  Calculate the output voltage for the above circuit, if in series with a resistance of 33 K, in series with a resistance of 10K, and .  Assume the feed back resistor as 330 .                            (5)

c.   How do we obtain a resistor in a monolithic integrated circuit?  Write a brief note on the construction of a base-diffused resistor.                          (4)