Digital circuits and analog devices

Tony Duell ard.p850ug1 at
Fri Dec 2 11:29:07 CST 2016

On Fri, Dec 2, 2016 at 3:57 PM, Paul Koning <paulkoning at> wrote:

> On the bit about grounds, I still have tucked away somewhere a very funny (but also serious) memory by Bob Steward (lead designer of a number of VAXen) entitled "Do not cut your grounds".  He described how a poorly chosen PCB layout turned a ground plane into a slot antenna, among other things.

However there are times when cutting away part of a ground plane can
reduce noise in
(say) a sensitive amplifier as it can prevent currents from other
parts of the circuit
going through that part of the ground plane.

> These are the sort of issues that supercomputer designers at CDC or Cray all understood thoroughly -- you can't build machines like that without this knowledge.  But a lot of logic designers working at slower speeds weren't taught properly and/or didn't really get it, and they might not get in trouble right away.

I do not believe it is possible to be a digital designer without also
understanding (and understanding well)
RF analogue electronics. There are plenty of people who claim to be
able to do that, suffice it to say
I've seen some of the messes so created.

A lot of the time it's not (just) the clock frequency that matters,
but also the rise time of the signals. So
a modern fast IC has to be decoupled, ground-planed, etc properly even
if you only clock it at 1Hz.


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