On Friday 04 July 2003 16:10, Mike Singer scribbled:
> Neil wrote:
> > Current-mode signals are generally less susceptible to
> > electronic noise (than voltage-mode signals), so great
> > for sensors in industrial or other noisy environments.
>
> Neil, what do these obscure phrases mean: "Current-mode
> signals", "voltage-mode signals"?

Fairly standard phrases, as I've seen them in various places before, and =
have=20
heard these spoken when talking to some support-reps.  I've heard this=20
usually with reference to sensors, but also somewhere with dc-dc converte=
rs. =20
"Current-mode signals" pretty much means -- "signals that generate a vari=
able=20
current output", and "Voltage-mode signals" means "signals that generate =
a=20
variable voltage output".


> Why not plain words describing actions: "setting output
> current" or "setting output voltage"?

Because the "standard" (?) phases seem to explain it in fewer words, and=20
again, I felt it to be fairly standard.  I could also say=20
"N-doped-silicon-sandwiched-between-bi-P-doped-silicon-material device" b=
ut=20
instead choose to say PNP transistor. :-)  Yeah, I'm in a smart-ass mood=20
today. :-)

There are lots of terms on this list that I don't know/recognize, so I lo=
ok=20
them up, and if not, then I ask.


> It's not "noise" consideration, when one choose to set
> output current instead of setting output voltage, I think.

It *is* actually a factor when choosing sensor output types in industrial=
=20
systems.  Do a google search, and I'm sure you'll come up with a bunch of=
=20
good answers why.


> It's just a humble desire to get a signal on the other
> end of the line, which doesn't depend on the line
> resistance. (Ask Olin how to set current in a line. He
> is well-known common-base and cascode scheme guru now :-)
>
> When setting output voltage you can fight noise by setting
> high enough voltage on a low enough load resistance.

Sure, but in many situations (given an existing system, existing voltages=
,=20
cost limitations, etc), you are limited by how high of a voltage you can=20
generate. In a vehicle for example, 4-20 mA should be better than a volta=
ge=20
signal due to the high noise level.  If your input "system" also has a lo=
w=20
input impedance, perhaps you can choose a current output instead of buffe=
ring=20
with another op-amp to raise the input impedance.  Etc, etc, etc.


> Mike.

Cheers,
-Neil.

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