• 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 = 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.