(SEM III) THEORY EXAMINATION 2017-18 ELECTONIC DEVICES AND CIRCUITS

This document contains the complete B.Tech Semester III – Theory Examination 2017–18 question paper for Electronic Devices and Circuits (REC-302). The paper consists of 2 printed pages, carries 70 marks, and evaluates a student’s conceptual and analytical understanding of semiconductor physics, electronic devices, amplifiers, MOSFET/BJT behavior, breakdown mechanisms, and oscillator theory. 

Section A — Short Conceptual Questions (14 Marks)

Section A contains seven brief questions designed to test basic theoretical knowledge of electronic devices:

Advantages of negative feedback in amplifiers

Meaning of Base Width Modulation (Early Effect) in BJTs

Concept of fluorescence

Difference between direct and indirect recombination lifetimes

Overview of Avalanche breakdown

Difference between EMOSFET and DMOSFET

Calculation of current gain (β) in CE configuration for α = 0.98

These questions ensure students understand core semiconductor effects and fundamental device behavior.

Section B — Detailed Analytical & Numerical Questions (21 Marks)

Students must attempt any three out of five questions. This section includes derivations, explanations, and numerical calculations:

Drawing CE amplifier with emitter resistance & deriving performance parameters

Discussing internal capacitances of BJT and MOSFET

Explaining luminescence, types of luminescence, and difference between fluorescence & phosphorescence, including fluorescence lamp application

Deriving Einstein relation between diffusion coefficient and mobility

Numerical problem on abrupt junction formation, including:

Depletion region width

Penetration depth on p-side & n-side

Using parameters: donor concentration, acceptor concentration, intrinsic carrier concentration, permittivity, and temperature

This section requires deep theoretical understanding and application of semiconductor equations.

Section C — Advanced Device Modeling & Circuit Analysis (35 Marks)

Students must attempt one part from each group. These questions test high-level understanding and design ability:

1. Feedback & Amplifier Analysis

Drawing four basic feedback topologies and comparing input/output resistances

Working of Common Source (CS) amplifier with source resistance, small-signal model & voltage gain derivation

2. Semiconductor Physics

Difference between direct and indirect bandgap semiconductors & effect of alloy composition

Concept of Fermi level, impact of doping & temperature on mobility, and calculation of equilibrium hole concentration for doped silicon

3. MOSFET Design & Characteristics

Designing a MOSFET circuit to achieve specific drain voltage, and finding effective resistance

Construction and I–V characteristics of a P-channel EMOSFET

4. BJT Applications & Biasing

BJT as amplifier and switch with circuit diagrams, waveforms, and expressions

Various biasing techniques for BJTs, explaining any two in detail

5. High Frequency Models & Oscillators

High-frequency hybrid-π model of MOSFET, showing fT=gm2π(Cgs+Cgd)f_T = \frac{g_m}{2\pi(C_{gs}+C_{gd})}fT​=2π(Cgs​+Cgd​)gm​​

Derivation of oscillation conditions and frequency expression for a phase-shift oscillator

Summary

This exam paper thoroughly assesses student understanding across:

Semiconductor physics

PN junction behavior

BJT & MOSFET parameters

Amplifier design and small-signal analysis

Feedback types & frequency response

Breakdown mechanisms & recombination

Oscillators and high-frequency modeling

It is a comprehensive academic resource for students studying electronic devices, circuits, and solid-state electronics.