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EC 3301 Electron Devices and Circuits question paper, April/May 2024

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Question Paper Code : 50956

B.E./B.Tech. DEGREE EXAMINATIONS, APRIL/MAY 2024.

Third Semester

Electrical and Electronics Engineering

EC 3301 — ELECTRON DEVICES AND CIRCUITS

(Common to : )

(Regulations 2021)

Time : Three hoursMaximum : 100 marks

Answer ALL questions.

PART A — (10 × 2 = 20 marks)

  1. 1.

    Determine V0 for the network shown in Fig (1). [Fig (1): input Vi is a triangular wave swinging between +16V and -16V; circuit: series resistor R from input to output, and from the output node to ground a diode (cathode at the output node, anode down) in series with a 4V battery (+ terminal toward the diode, - terminal to ground); output Vo taken across the diode-battery branch]

  2. 2.

    What is the condition for Laser Action?

  3. 3.

    Define alpha, beta and gamma of the transistor and mention the relationship of the terms.

  4. 4.

    Differentiate between Enhancement and Depletion MOSFET.

  5. 5.

    Why are bypass and coupling capacitors used in amplifier circuits?

  6. 6.

    Why harmonic distortion occurs in amplifier and how can it be reduced?

  7. 7.

    State two advantages and two disadvantages of single tuned amplifiers.

  8. 8.

    What are the coupling schemes used in multistage amplifiers?

  9. 9.

    State Barkhausen criterion for sustained oscillation. What will happen to the oscillation, if the magnitude of the loop gain is greater than unity?

  10. 10.

    What is meant by positive feedback and negative feedback?

PART B — (5 × 13 = 65 marks)

  1. 11.
    (a)
    • (i)With necessary diagrams explain the structure and operation of PN junction diode.(8)
    • (ii)Briefly explain about the PN junction capacitances.(5)
  2. Or
  3. (b)
    • (i)Explain the operation of Zener diode and its VI characteristics.(8)
    • (ii)Explain how Zener diode acts as a voltage regulator.(5)
  4. 12.
    (a)

    Explain the structure, operation and V-I characteristics of BJT.

  5. Or
  6. (b)

    With neat diagram explain the structure, operation and V-I characteristics of UJT and IGBT.

  7. 13.
    (a)
    • (i)Explain and derive the voltage and current gain expressions for CB configuration using hybrid models.(9)
    • (ii)Analyze and determine Ic, IB and dc voltage at the collector of the transistor amplifier circuit shown in fig. 13. a (ii) [Fig. 13. a (ii): NPN transistor with emitter grounded; base fed through R_BB = 100 k ohm from a signal source V_I in series with V_BB = 3 V to ground; collector connected through R_C = 3 k ohm to V_CC = +10V; output V_C + V_O taken at the collector](4)
  8. Or
  9. (b)
    • (i)Draw the small signal equivalent circuit of MOSFET common drain amplifier and derive the expressions for voltage gain, input impedance and output impedance.(9)
    • (ii)Consider the amplifier circuit shown in Fig 13. b (ii) The FET is specified to have V_t = 0.4V, k_n' = 0.4 mA/V^2, W/L = 10 and lambda = 0. Also, let V_DD = 1.8V, R_D = 17.5 k ohm and V_GS = 0.6V. Find I_D and V_DS. [Fig. 13. b (ii): n-channel MOSFET with source grounded; gate driven by signal v_gs in series with dc source V_GS; drain connected through R_D to V_DD (drain current i_D); output V_DS taken at the drain](4)
  10. 14.
    (a)

    What is a differential amplifier? Draw the circuit diagram and explain the working principle of BJT differential amplifier. Explain the circuit operation of common mode and differential mode.

  11. Or
  12. (b)

    Explain the basic principle of tuned amplifiers using MOSFET and derive the expression for its center frequency gain. Also discuss their characteristics and losses.

  13. 15.
    (a)

    With neat diagram explain voltage series and current series amplifier. Derive the expression for transresistance gain, i/p resistance, o/p resistance and the voltage gain.

  14. Or
  15. (b)
    • (i)Draw the circuit diagram of RC phase shift oscillator and briefly explain its working principle. Also derive the expression for its gain.(8)
    • (ii)Design a phase shift oscillator, to oscillate at 1 KHz.(5)

PART C — (1 × 15 = 15 marks)

  1. 16.
    (a)
    • (i)Explain the structure, operation and V-I characteristics of JFET.(8)
    • (ii)The parameters of the transistor in the circuit in Figure 16.a (ii) are beta = 150 and V_A = infinity. (1) Determine R1 and R2 to obtain a bias-stable circuit with the Q-point in the center of the load line. (2) Determine the small-signal voltage gain AV = V_O/V_S. [Figure 16. a (ii): NPN transistor; R1 from V+ = +5V to the base and R2 from the base to V- = -5V; source V_S coupled to the base through capacitor C_C; R_C = 1.2 k ohm from V+ to the collector, output V_O at the collector; R_E = 0.2 k ohm from the emitter to V-](7)
  2. Or
  3. (b)
    • (i)Draw the circuit of a Colpitt oscillator and explain its working principle.(8)
    • (ii)Consider the MOSFET feedback amplifier shown in figure 16.b (ii). The transistor parameters are V_TN = 0.5V, K_n = 0.5 mA/V^2 and lambda = 0. Determine the small-signal voltage gain Av = Vo/Vi. [Figure 16.b (ii): NMOS differential pair M1, M2 with drain resistors R_D = 7 k ohm each to V+ = 5V; common sources connected to a current source I_Q = 1 mA to V- = -5V; input v_i at the gate of M1; output v_o at the drain of M2; feedback divider R1 = 200 k ohm from v_o to the gate of M2 and R2 = 200 k ohm from the gate of M2 to a 1.5 V battery (- terminal toward R2, + terminal to ground)](7)

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