🔌 Electrical Engineering II: Electronics

What you’ll learn

1. From Circuits to ElectronicsDistinguish electronics from circuit theory via active devices, from the Audion to ENIAC's limits.Electronics begins with active devices that let small signals control large ones. De Forest's 1906 Audion triode created amplification, long-distance telephony, and radio, but tube machines like the 17,468-tube, 150 kW ENIAC exposed the need for something small, cold, and solid.
2. Semiconductors: The In-Between MaterialsExplain semiconductors, nine-nines purity, and N/P doping.Silicon conducts poorly when pure but is transformed by parts-per-million doping: phosphorus donates free electrons (N-type), boron creates holes (P-type). Czochralski-grown single crystals, sliced into wafers, are the canvas of all chipmaking.
3. The PN Junction and the DiodeDescribe the PN junction, depletion zone, and diode bias states.Joining P and N silicon forms a depletion zone with a ~0.7 V barrier: forward bias collapses it and current flows, reverse bias widens it and blocks. Crystal-detector radios used crude point-contact diodes decades before the physics was understood.
4. Diodes at Work: Rectifiers, LEDs, ZenersApply diodes in rectifiers, LEDs, and Zener references.Four diodes in a bridge turn AC into DC in every charger; LEDs emit photons on recombination (blue LEDs earned the 2014 Nobel); Zeners run in controlled reverse breakdown to pin precise reference voltages.
5. 1947: The TransistorRecount the transistor's 1947 invention and its cultural detonation.Bardeen and Brattain demonstrated the point-contact transistor in December 1947; Shockley's junction design made it practical, and the trio shared the 1956 Nobel. The pocket transistor radio then made electronics personal and seeded Silicon Valley's founding companies.
6. Inside the Bipolar TransistorExplain BJT structure and current gain.A BJT is an NPN or PNP sandwich whose deliberately thin base lets emitter carriers sweep into the collector, so collector current is β (≈50-300) times base current. The valve analogy captures the essence: a weak flow shaping a strong one.
7. Switch or Amplifier: The Transistor's Two JobsContrast the transistor's switch and amplifier modes.Saturation and cutoff make the transistor a wear-free nanosecond switch — the atom of digital logic — while the active region between them amplifies faithfully. Clipping beyond the limits is distortion, fought in hi-fi and celebrated in guitar amps.
8. MOSFETs: The Most-Made Object in HistoryExplain MOSFET field-effect operation and why it dominates.The MOSFET's insulated gate steers a channel by electric field alone, drawing near-zero drive power; with CMOS pairing and extreme shrinkability, it became the basis of all digital chips — an estimated 13 sextillion made by 2018, history's most manufactured object.
9. Amplifiers: Making Signals Bigger, HonestlyQuantify gain in decibels and compare amplifier classes.Gain in dB (20·log₁₀ for voltage) turns multiplied stages into added numbers; real chains need 60-80 dB. Class A trades efficiency for purity, class B the reverse, and class AB — nearly universal in audio — idles both output devices slightly to erase crossover distortion.
10. The Op-Amp: A Perfect Amplifier in a ChipIntroduce the op-amp's differential input, huge gain, and negative feedback.An op-amp is a complete high-gain differential amplifier in one chip (the 1968 μA741 made it a commodity). Negative feedback, Harold Black's 1927 idea, converts its wild 100,000× gain into precise, resistor-set behavior.
11. Op-Amp Circuits You Can BuildAnalyze the inverting amplifier and comparator using the golden rules.With feedback, gain = −Rf/Rin via the virtual-ground trick; without feedback the op-amp becomes a comparator that squares up analog signals. Both are minutes of breadboard work — the fastest route to owning the concepts.
12. Transistors as Logic: Digital ElectronicsBuild digital logic from transistor switches and truth tables.Digital circuits gain noise immunity by allowing only two states, and gates — AND, OR, NAND — are small transistor circuits computing truth tables. NAND alone is universal: any computer can, in principle, be wired entirely from it.
13. The Integrated Circuit and Moore's LawTrace the integrated circuit from Kilby and Noyce to the 4004 and Moore's law.Kilby's 1958 one-chip circuit and Noyce's planar wiring solved the tyranny of numbers; Intel's 2,300-transistor 4004 put a CPU on a chip in 1971. Moore's 1965 doubling observation became a 50-year industry schedule ending in hundred-billion-transistor processors.
14. Oscillators, Timers, and RadioExplain oscillators, the 555 timer, and resonant tuning in radio.Positive feedback plus a timing element makes an amplifier oscillate, and piezoelectric quartz (32,768 Hz in every watch) provides superb stability. The 555 timer (1972) remains a billion-a-year classic, and radios select stations by LC resonance — the principle visible in a century-old crystal set.
15. Powering It All — and Where Electronics Goes NextFollow the power chain and preview power electronics' future.Switch-mode supplies rectify, chop at high frequency with MOSFETs, and regulate by duty cycle — smaller and cooler than linear designs. Scaled to IGBTs and SiC, the same switching runs EV drivetrains and solar grids, and a phone board recaps the entire course in one palm.

Questions this course answers

Grounded in trusted sources

• Horowitz & Hill, 'The Art of Electronics', 3rd ed. (Cambridge University Press, 2015)
• Sedra & Smith, 'Microelectronic Circuits', 8th ed. (Oxford University Press, 2020)
• Riordan & Hoddeson, 'Crystal Fire: The Birth of the Information Age' (W. W. Norton, 1997)
• Gordon Moore, 'Cramming More Components onto Integrated Circuits', Electronics 38 (1965)
• Nobel Prize documentation — Physics 1956 (transistor), 2000 (integrated circuit), 2014 (blue LED)
• Ron Mancini (ed.), 'Op Amps for Everyone' (Texas Instruments, 2002)
• IEEE Spectrum, '13 Sextillion & Counting: The Long & Winding Road to the Most Frequently Manufactured Human Artifact in History' (2018)

Every Wunder lesson is built from real, reputable sources — never invented.

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