25 Dec
2025
25 Dec
'25
3:25 p.m.
On 2025Dec 25,, at 12:32 PM, Martin Bishop <mjd.bishop(a)emeritus-solutions.com>
wrote:
Series R on logic outputs are a classic "taming" mechanism, they also provide
access to the net for more extreme measures (eg C to ground). Usu 22R or 33R close to the
driver to bring the probable source impedance to 50Z - matching the nominal track
impedance. The design may be evolved to include parallel (DC) termination or AC
termination (series R & C) for multidrop loads. For 2025 circuits much of this is
moot, the track lengths are so short, in the 1980's it was different ...
IBIS models for devices of interest and the wisdom of HoJo's oeuvre are the classic
references
https://www.amazon.co.uk/High-Speed-Signal-Propagation-Advanced/dp/01308440…
The series R/L in a signal line for parisitic oscillation/ringing suppression actually
goes back to the early tube days, well before logic, where they can be found on tube
grids, esp. power amps, even audio freq.