Electronic Science
Electronic Science in UGC NET examines the whole signal chain, from carrier transport in devices to system-level design. Questions mix short numericals with concept checks, so the paper rewards unit-wise fluency rather than isolated formula memorisation.
What the paper covers
Expect recurring clusters: network theory (Thevenin/Norton, transients, two-port parameters), semiconductor devices (pn junction, BJT, MOSFET, biasing), analog circuits (op-amps, feedback, oscillators), digital electronics (Boolean algebra, sequential logic, memories), signals and systems (convolution, Fourier/Laplace/Z transforms), control systems (stability, root locus, Bode plots), communication (AM/FM, noise, Shannon capacity), and electromagnetics/microwave (transmission lines, Smith chart, waveguides).
Rules that decide marks
- Thermal voltage (V_T = kT/q \approx 25.85\ \text{mV}) at 300 K, not a fixed 26 mV; it rises with temperature.
- Diode equation (I = I_S(e^{V/\eta V_T} - 1)); (\eta = 1) for ideal drift, about 2 when recombination dominates.
- The op-amp virtual short holds only when negative feedback is present.
- A two-port is reciprocal if (z_{12} = z_{21}) and symmetric if (z_{11} = z_{22}).
Worked example
A silicon diode with (I_S = 1\ \text{pA}), (\eta = 1), is forward biased at 0.6 V at 300 K. Find (I).
(V_T = 25.85\ \text{mV}), so (V/V_T = 0.6/0.02585 \approx 23.2). Then (e^{23.2} \approx 1.2\times10^{10}). Thus (I \approx 1\times10^{-12} \times 1.2\times10^{10} = 12\ \text{mA}). The (-1) term is negligible here but must be retained near 0 V or in reverse bias.
Traps
- Misreading (I_S) as 1 nA instead of 1 pA shifts the answer by 1000×; track prefixes explicitly.
- Applying the virtual short to a comparator or an open-loop op-amp gives nonsense.
- Quoting a transform without its ROC; causality and stability depend on the ROC, not the algebraic expression alone.
- Confusing dB for power and voltage: 3 dB is a factor of 2 in power but about 1.41 in voltage.