Electronics and Telecommunication Engineering Division: Signals, Devices, and Links
Core concepts to master
Expect questions spanning analog devices (diode models, BJT and MOSFET biasing, op-amp ideal assumptions), digital electronics (Boolean algebra, flip-flops, counters, logic families), signals and systems (Fourier and Laplace transforms, convolution, sampling and aliasing), and communication (modulation, bandwidth, noise figure, link budgets). A candidate should be able to move between time and frequency domains and to state the ideal op-amp rules: infinite input impedance, zero output impedance, and virtual short between inputs under negative feedback.
Traps that appear in questions
- Ignoring the Nyquist criterion: sampling below twice the highest frequency folds energy to a false low frequency.
- Confusing dBm with dBW; 0 dBm is 1 mW, 30 dBm is 1 W.
- Applying the virtual-short rule to a comparator or open-loop circuit - it holds only with negative feedback.
- Mixing FM and AM bandwidth: Carson's rule gives BW ≈ 2(Δf + fm) for FM, not 2fm.
- Forgetting that noise figure is a power ratio in dB and that cascaded stages are dominated by the first stage's gain.
Worked example
An FM signal with peak deviation 75 kHz and modulating tone 15 kHz: Carson's rule gives BW ≈ 2(75 + 15) = 180 kHz. Rule of thumb: in a cascade, Friis' formula means the first amplifier's gain suppresses later noise contributions, so always place a low-noise, high-gain stage first. For link budgets, received power (dBm) = transmit power + gains − losses, and every term must be in the same unit before summing.