4 Jun
2006
4 Jun
'06
9:13 p.m.
Tony wrote:
True enough. I don't set up a TDR every time I wire up a simple logic
circuit.. (I have been known to assume that a twisted pair of wire-wrap
wire with 3 twists per inch has a chracteristic impedance of 120 Ohms,
though. That is near enough for most circuits!).
I haev never understood how you can understand
digitial electronics
properly and not understand analogue electronics. I certaimly couldn't
understnad digital stuff until I understood things like transmision
lines, termination, etc.
You can understand it well enough to use for many
practical purposes by just
knowing a few "rules of thumb"*. A better, but still not necessarily detailed, understanding of the analogue background can
help considerably in
some of the more tricky situations - especially if you are
"stretching"/abusing the "rules". Too detailed a consideration of
the
background can actually get in the way [the best example I have of this is
the realisation that one has much more tolerance in termination than
analogue theorists tend to expect - half or double the normal termination
A good understanding includes an understanding of tolerances IMHO. I have
no time at all for so-called engineers (and I've met plenty of them) who
can calculate component values to 10 significant figures but have no idea
how accurate they actually need to be (hint, for pull-up resistors a
factor of 10 may make little difference).
A good undersanding of the analogue side of 'digital eleectronics'
includes, therefore, knowing when you need to terminate a signal, and how
accurate that teminator needs to be.
-tony