The whole point of this chapter is to give you tools you actually use. Here are a few extra real-world connections worth knowing.
9.1 USB termination is impedance matching
A USB cable is a transmission line with characteristic impedance near 90 Ω differential. At USB 3.x speeds (5 Gbps and up), any mismatch between the cable and the chip's output stage causes reflections that corrupt data and close the eye diagram. USB host and device chips include carefully tuned termination resistors so signals are absorbed rather than reflected. This is Maximum Power Transfer at gigahertz, but optimizing signal integrity rather than power efficiency. Chapter 9 covers transmission lines in depth.
9.2 Switching power supplies use mesh-style energy storage
Buck, boost, and buck-boost converters consist of a transistor switch, inductor, diode (or synchronous switch), capacitor, and load. Across the two switch phases the topology changes: one phase charges the inductor, the other discharges it into the output. Mesh-style analysis gives the inductor current and capacitor voltage waveforms in each phase, sizing components for the desired ripple. Modern converters run at hundreds of kHz to several MHz, where the transient analysis we just learned is daily bread.
9.3 Antenna feeder lines need Thevenin-equivalent matching
A radio transmitter's output stage looks like a Thevenin source from the antenna's side. To transfer signal power efficiently, the feeder line and antenna must match the transmitter's Thevenin impedance. Mismatch creates standing waves, reflects power back into the transmitter (potentially damaging the output stage), and reduces radiated power. Antenna tuners are matching networks of L and C that convert one impedance into another to restore the match.
9.4 TDR for tamper detection
A time-domain reflectometer (TDR) sends a fast voltage step down a cable or PCB trace and measures reflections. Reflections only occur at impedance discontinuities, so a TDR can detect a break, a bad solder joint, an unauthorized splice, or even a tiny probe tap on a secure line. From a hardware-security standpoint, TDR is a tamper-evidence tool: if the impedance profile changes from baseline, something has changed physically. The combination of transmission-line theory and Thevenin-style impedance reasoning is what makes TDR work.