BE Computer Engineering (IOE, TU) Basic Electronics Engineering (IOE, EX 451) Question Paper 2078

(a) Explain the input and output characteristics of an n-p-n transistor connected in common-emitter (CE) configuration, clearly indicating the active, cut-off and saturation regions on the output characteristics. [6]

(b) For the voltage-divider biased CE amplifier shown below, $V_{CC} = 12\,\text{V}$, $R_1 = 40\,\text{k}\Omega$, $R_2 = 10\,\text{k}\Omega$, $R_C = 2\,\text{k}\Omega$, $R_E = 1\,\text{k}\Omega$ and $\beta = 100$. Determine the operating point ($I_{CQ}$ and $V_{CEQ}$) and comment on the stability of the bias. [6]

(a) Define the ideal characteristics of an operational amplifier and explain the significance of the virtual ground concept in an inverting configuration. [5]

(b) Design an op-amp circuit that produces the output $V_o = -(3V_1 + 5V_2 + 2V_3)$ from three input voltages $V_1$, $V_2$ and $V_3$. Choose suitable resistor values and draw the complete circuit, stating any assumptions. [7]

(a) With a neat circuit diagram and relevant waveforms, explain the operation of a full-wave bridge rectifier. Derive expressions for its average (DC) output voltage and ripple factor. [7]

(b) A full-wave bridge rectifier fed from a transformer with peak secondary voltage of 30 V uses a shunt capacitor filter of $470\,\mu\text{F}$ and feeds a load of $1\,\text{k}\Omega$ at 50 Hz mains frequency. Estimate the DC output voltage and the peak-to-peak ripple voltage. [5]

(a) Explain the construction and operation of an n-channel enhancement-type MOSFET. Sketch its drain and transfer characteristics and define the threshold voltage. [7]

(b) Compare a JFET with a BJT with respect to input impedance, control mechanism, noise performance and the meaning of the term 'unipolar device'. [5]

Sketch and explain a positive clipper and a positive clamper circuit using a diode. Draw the output waveform for a sinusoidal input of $\pm 10\,\text{V}$ in each case.

A Zener diode having $V_Z = 6.2\,\text{V}$ is used as a voltage regulator with a series resistance of $220\,\Omega$ from a 12 V supply. If the load draws 15 mA, calculate the current through the Zener diode and the power dissipated in it. State the condition for the regulator to maintain regulation.

(a) Convert $(2A.5)_{16}$ to its decimal and binary equivalents. [3]

(b) Perform the subtraction $(1011\,0010)_2 - (0110\,1101)_2$ using 2's complement arithmetic and verify your result in decimal. [3]

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

(b) Simplify the Boolean expression $F = A\bar{B} + AB + \bar{A}B$ and implement the simplified expression using only NAND gates. [3]

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

For an op-amp integrator, derive the relationship between the output and input voltages. Explain why a high-value resistor is connected in parallel with the feedback capacitor in a practical integrator.

Explain the formation of the depletion region in an unbiased p-n junction. Describe how the width of the depletion region and the junction current change under forward bias and reverse bias.

Define the parameters $\alpha$ and $\beta$ of a transistor and derive the relationship between them. If a transistor has $\beta = 120$, calculate $\alpha$ and the value of the leakage current effect described by $I_{CEO}$ in terms of $I_{CBO}$.