Don’t Leave Home Without It: Redrivers for USB Type-C Designs (.PDF Download)

The advertising slogan in the title refers to the American Express card, a classic ad campaign that began in 1975. That year was also when Microsoft was founded, and a year when your humble writer finally abandoned dreams of musical fame and fortune and applied to engineering school.

Back then, the newest thing in serial communications for the home was the X10 protocol that used the ac power line to send control signals to lamps and thermostats; the X.10 data rate was a leisurely 120 bits per second (b/s).

We’ve raised the bar a little since those days: In 2017, the USB Type-C set of specifications rules the roost. The complete set comprises the USB Type-C connector specification: the USB 3.1 interface specification with a maximum data rate of 10 Gb/s; and the USB Power Delivery specification (USB PD) for power-related functions. Although they’re often mentioned in same breath, a USB system can support one specification but not the others—USB Type-C but not USB 3.1 or USB PD, for example.

Two problems confronting X.10 design engineers in 1975 were excessive attenuation of signals as they propagated down the ac wires, and interference caused by nearby equipment.

Plus ça change, plus c’est la même chose… Although the data rate has increased by orders of magnitude compared to X.10, signal integrity issues still plague designers today. At gigabit-per-second speeds, a host of variables can affect signal integrity, including transmission-line effects, impedance mismatches, crosstalk, signal routing, bus termination designs, electrostatic-discharge (ESD) protection devices, and printed-circuit-board (PCB) grounding.