-------- In message <20190709053037.2d244406...@ip-64-139-1-69.sjc.megapath.net>, Hal Mu rray writes:
>What's the advantage of a PSRR in the MHz range? Is it as simple as reducing >the number and size of the caps needed? The caps have only ever acted as a low-pass filter, to move the noise down in the frequency range of the power-supply regulation. The digital switching noise happens in (pico- and nano-)Coloumbs, not in volts or amps, which means that as the supply voltage decreases, it becomes percentwise larger voltage noise. To deal with that passively you would need bigger caps with better high frequency performance, and lower ESR and more, expensive PCBs (more layers etc.) The trend is therefore to move the corner frequency of the passive low-pass filter higher, that allows you to use ceramic capacitors, instead you must increase the bandwidth of the final power-supply, typically a LDO, and move it physically closer to the load. On high-end kit, it is not uncommon to see a big chip surrounded by a ring of tiny LDO's spaced as little as a centimeter apart along its periphery. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.