Electronics and Communication Engineering
Electronics and communication engineering questions test device behaviour, circuit analysis, modulation and digital logic. The JTO paper favours fundamentals that connect a block diagram to a measurable voltage, bandwidth or bit rate, so be ready to calculate rather than only define.
Core rules and concepts
- Diode: forward bias lowers resistance; silicon knee ≈0.7 V; Zener regulation uses reverse breakdown.
- BJT: active mode has forward BE and reverse BC; saturation has both forward; cut-off has both reverse. β = IC/IB.
- MOSFET: gate is insulated, so input current is very low; enhancement vs depletion and n vs p channel matter.
- Op-amp ideal: infinite gain and input impedance, zero output impedance. Inverting gain = −Rf/Rin; non-inverting = 1 + Rf/Rin.
- AM DSB-FC bandwidth = 2fm and has poor power efficiency; FM has constant envelope and Carson bandwidth ≈ 2(Δf + fm).
- Shannon: C = B log2(1 + S/N), with S/N as a linear power ratio, not dB.
- Digital logic: Boolean algebra, De Morgan, K-maps, flip-flops; ADC resolution depends on bits and reference.
- Transmission line: characteristic impedance, reflection coefficient and VSWR; antenna length relates to wavelength.
Worked example
Inverting op-amp with Rf = 20 kΩ, Rin = 4 kΩ and Vin = 0.2 V: gain = −20/4 = −5, so Vout = −1.0 V. Check that negative feedback exists and that ±1.0 V is inside the op-amp supply rails; otherwise the output clips and the linear formula fails.
Traps that cost marks
Apply the virtual-short rule without negative feedback; treat β as α; use fm instead of 2fm for AM bandwidth; insert a dB SNR directly into Shannon; ignore op-amp rails; confuse FM deviation with modulating frequency.