Analog Electronics
A diode conducts one way and a transistor amplifies — but only because of what carriers are doing inside the material. These topics animate the device physics first, then the circuit that depends on it.
Start from the beginning →9 topics you can watch now, 15 still to come.
Semiconductors and the junction
Why a material that is neither conductor nor insulator is the useful one.
- Intrinsic and extrinsic semiconductors
- Drift and diffusion current
- Diode I-V characteristic and models
Diode circuits
The first useful thing a one-way device buys you.
- Rectifiers and SmoothingWatch the negative half disappear and the peaks flatten — then find out why the capacitor that smoothed it made the current spiky.
- Zener Diodes and Voltage RegulationA diode operated in the region every other topic told you to avoid. It runs hottest at no load, which is the opposite of intuition.
- Clippers and clampers
- Precision rectifiers
Bipolar junction transistors
Two junctions, one small current controlling a large one.
- How a BJT Works"Two diodes back to back" predicts nothing. The thin shared base is why 99% of the carriers cross, and why β lands near 100.
- Biasing and the Q-Pointβ varies 4:1 for one part number, so any bias scheme that depends on it depends on luck. The fix is a feedback loop in a DC circuit.
- Small-Signal AnalysisReplace a thoroughly non-linear device with a straight line that is wrong everywhere except near one point — and get the whole of linear circuit theory in exchange.
- CE, CB and CC configurations compared
- Multi-stage and differential amplifiers
Field-effect transistors
Control by voltage rather than current — and the modern default.
- JFET operation
- Common-source amplifier design
- CMOS inverter
Operational amplifiers
A gain block so large you design with feedback instead.
- Summing, difference and instrumentation amplifiers
- Integrator, differentiator and comparator
- Active filters
Feedback and oscillators
The same loop that stabilises a gain can make it oscillate.
- Four feedback topologies in detail
- Crystal oscillators and phase noise
About Analog Electronics
Analog electronics is about devices that are deliberately not switches. A transistor used digitally is either on or off; used analogically it sits in between, and that in-between region is where amplification, regulation and oscillation come from.
The subject moves in layers of abstraction, and knowing which layer you are on prevents most confusion. Underneath is semiconductor physics — the PN junction, carriers, depletion. Above that are device models that let you calculate without the physics. Above that are building blocks: amplifier stages, feedback loops, op-amp configurations you use without re-deriving.
Feedback is the idea worth the most here. Applied deliberately it makes an amplifier's gain depend on resistors rather than on an unreliable transistor; applied accidentally it makes an oscillator. The same mathematics governs both, which is why they are taught together.
What to know first
- Electric Circuit Analysis, especially Thevenin equivalents
- Willingness to accept a device model before its physics is complete
Where it gets used
- Designing a power supply that holds its voltage under changing load
- Choosing an op-amp configuration for a sensor signal
- Recognising unintended oscillation as a feedback problem