30 Mar
2017
30 Mar
'17
9:07 p.m.
On Thu, Mar 30, 2017 at 9:13 PM, Noel Chiappa via cctalk
<cctalk at classiccmp.org> wrote:
I'm still not clear, from the discussion, how
exactly that nice 'square-wave'
interference is happening - could it be capacitative crosstalk? (I'd have
thought capacitative cross-talk would be inverted - driving a positive voltage
on one 'side' of the 'capacitor' would, I would think, induce an
oppposing
voltage on the other. But I'm clearly no EE! :-)
The fundamental rule is 'You can't change the voltage across a capacitor
instantly'. There is a related one 'You can't change the current through
an inductor instantly'. It (of course) doesn't matter if said capacitor
or inductor is an actual component or 'strays'.
So instantaneously, a capacitor acts like a constant voltage drop.
If the charge on the capacitor doesn't change much (fast signals,
high resistors so not much current flow), the 2 sides of the
capacitor will be much the same signal (possibly with a
constant voltage offset).
-tony