• Tags: diode-characteristics, transistor, logic-gates
• Difficulty: Moderate

I-V characteristics of diode (forward): negligible current until threshold (~0.7 V for Si, ~0.3 V for Ge), then exponential rise. Reverse: tiny saturation current $I_0$ (~nA) until breakdown. LED: similar forward characteristic but higher threshold (1.5-3 V depending on color); emits light above threshold. Zener: designed reverse breakdown at $V_Z$ — current increases sharply while voltage remains constant (voltage regulator application). Transistor input characteristics ($I_B$ vs $V_{BE}$ at constant $V_{CE}$): similar to a forward-biased diode. Transistor output characteristics ($I_C$ vs $V_{CE}$ at constant $I_B$): three regions — cutoff ($I_B$ = 0, $I_C$ ≈ 0), active ($I_C$ = beta*$I_B$, nearly independent of $V_{CE}$), saturation ($I_C$ limited, $V_{CE}$ small). Current gain beta = \frac{Delta_I_C}{Delta_I_B} from the output curves. Logic gate verification: apply all input combinations (00, 01, 10, 11) and measure output voltage; classify as HIGH or LOW; compare with the expected truth table.