BE Computer Engineering (IOE, TU) Basic Electronics Engineering (IOE, EX 451) Question Paper 2079

(a) Explain the formation of a p-n junction and derive the relationship between the diode current and the applied voltage using the diode equation, clearly defining each term. (6)

(b) For the silicon diode circuit shown, the input is a sinusoidal signal $v_i = 10\sin\omega t$ V applied to a positive clipper. Sketch the output waveform and explain its operation. Assume the diode cut-in voltage is 0.7 V. (6)

(a) Draw the circuit of a voltage-divider (potential-divider) bias configuration for an npn BJT and derive the expression for the collector current $I_C$. Explain why this configuration provides better bias stability than fixed-bias. (7)

(b) For a voltage-divider bias circuit with $V_{CC}=18$ V, $R_1=39\text{ k}\Omega$, $R_2=10\text{ k}\Omega$, $R_C=2\text{ k}\Omega$, $R_E=1\text{ k}\Omega$ and $\beta=120$, determine the Q-point ($I_{CQ}$ and $V_{CEQ}$). (5)

(a) Define an ideal operational amplifier and list four of its ideal characteristics. Using the virtual-ground concept, derive the closed-loop voltage gain of an inverting amplifier. (8)

(b) Design an op-amp summing amplifier that produces an output $v_o = -(2v_1 + 4v_2 + v_3)$. Show all resistor values assuming a feedback resistor of $R_f = 40\text{ k}\Omega$. (5)

(c) Explain, with a circuit diagram, the working of an op-amp integrator and write its output expression. (3)

(a) With suitable diagrams, explain the construction and operation of an n-channel JFET. Sketch and explain its drain and transfer characteristics, indicating the pinch-off voltage. (8)

(b) Differentiate between depletion-type and enhancement-type MOSFETs in terms of construction and the relationship between gate voltage and drain current. (4)

Draw the circuit of a full-wave bridge rectifier and explain its operation with input and output waveforms. Derive the expression for its ripple factor and explain how a capacitor filter reduces ripple.

(a) Convert $(2AF.C)_{16}$ to its decimal and binary equivalents. (3)

(b) Perform the subtraction $(1011)_2 - (0110)_2$ using 2's complement arithmetic and verify your result. (3)

(a) State and prove De Morgan's theorems. (3)

(b) Simplify the Boolean function $F(A,B,C,D)=\sum m(0,1,2,5,8,9,10)$ using a Karnaugh map and implement the simplified expression using only NAND gates. (5)

State the Barkhausen criterion for sustained oscillations. With a neat block diagram, explain the working principle of an RC phase-shift oscillator and write the expression for its frequency of oscillation.

Explain how a Zener diode acts as a voltage regulator. For a Zener regulator with $V_Z=10$ V, $R_S=1\text{ k}\Omega$, an unregulated input of 20 V and a load resistance $R_L=2\text{ k}\Omega$, calculate the current through the Zener diode.

Draw and explain the input and output characteristics of a BJT in common-emitter (CE) configuration. Identify the active, saturation and cut-off regions on the output characteristics.

(a) Define CMRR, slew rate and input offset voltage of an operational amplifier. (4)

(b) With a circuit diagram and transfer characteristic, explain the operation of an op-amp Schmitt trigger and state one practical application. (4)