Analog Electronics

Diodes, transistors, amplifiers and power. The devices and circuits that shape continuous signals: diodes, rectifiers and Zeners; BJTs, MOSFETs and JFETs; amplifiers and op-amps; feedback and oscillators; active filters; and linear and switching voltage regulators.

• Diodes & the PN Junction — The diode is the simplest semiconductor device — a one-way valve for current. Learn doping and the PN junction, forward and reverse bias, the Shockley equation and 0.6–0.7 V drop, I–V characteristics, diode types (signal, Schottky, LED, photodiode, varactor), and practical uses such as LED current limiting and reverse-polarity protection.
• Rectifiers — Rectifiers convert AC to DC. Learn half-wave, centre-tapped and bridge single-phase circuits, three-phase bridges, capacitor filtering and ripple, PIV ratings, and the design of a complete linear DC supply.
• Zener Diodes — Zener diodes break down at a precise reverse voltage and hold it nearly constant. Learn Zener and avalanche breakdown, the shunt regulator design (series resistor, minimum Zener current, power dissipation), line and load regulation, voltage references, and TVS protection.
• Bipolar Junction Transistors (BJT) — The BJT amplifies current: a small base current controls a large collector current. Learn NPN/PNP structure, operating regions (cut-off, active, saturation), current gain β, voltage-divider biasing, DC operating point (Q-point), transconductance, and the BJT as a switch and amplifier.
• MOSFETs & JFETs — Field-effect transistors are voltage-controlled: the gate voltage sets the channel current with almost no gate current. Learn JFET and MOSFET structure, enhancement vs depletion, N- vs P-channel, threshold voltage, square-law and triode regions, transconductance, R_DS(on) switching, gate charge and logic-level drive.
• Amplifiers — Amplifiers make small signals bigger. Learn gain in V/V and decibels, common-emitter/source, common-collector (follower) and common-base configurations, input and output impedance, cascading stages, frequency response (coupling capacitors, bandwidth), distortion and amplifier classes A, B, AB, D.
• Operational Amplifiers — The op-amp is the universal analog building block. Learn the ideal op-amp rules (virtual short), inverting, non-inverting, voltage follower, summing, difference, instrumentation, integrator and comparator circuits, plus real limitations: gain–bandwidth product, slew rate, offset, input bias current and rail-to-rail behaviour.
• Feedback — Feedback returns part of the output to the input. Learn negative vs positive feedback, the closed-loop gain formula A/(1 + Aβ), loop gain, desensitivity, bandwidth extension, impedance changes, the four feedback topologies, and stability (Barkhausen, phase margin).
• Oscillators — Oscillators generate repeating signals — the heartbeat of every digital system and radio. Learn the Barkhausen criterion, RC phase-shift and Wien-bridge oscillators, LC Colpitts/Hartley, crystal oscillators and their stability, relaxation oscillators and the 555 timer, VCOs and PLLs.
• Filters — Filters pass wanted frequencies and reject others. Learn low-pass, high-pass, band-pass and notch responses, passive RC/LC and active op-amp filters, filter order and roll-off, Butterworth, Chebyshev and Bessel approximations, Sallen–Key design, and anti-aliasing filters for ADCs.
• Voltage Regulators — Every circuit needs stable supply rails. Learn linear regulators (series pass, LDO dropout, 78xx, LM317), efficiency and heat, thermal design, switching regulators (buck, boost, buck-boost) with duty cycle and inductor ripple, noise and layout, and choosing between linear and switching.