> On Fri, Apr 14, 2000 at 12:19:45PM +0100, Kenn Humborg mentioned:
> > > On Fri, Apr 14, 2000 at 12:09:37PM +0100, Kenn Humborg mentioned:
> > > > So the question comes down to "are the extra conductors in a UDMA66
> > > > cable used for differential signalling or for ground wires"?
> > >
> > > And, does it matter, as they are pretty similar ideas, with pretty
> > > similar effects ? <grin>
> >
> > They're completely different ideas. They require very different
> > driver and receiver designs and have very different high-frequency
> > and noise characteristics.
>> How would drivers differ ?
If the two conductors in the pair are Signal and GND, then
the driver only needs to drive the signal line. That's one
output stage. The other line is connected directly to
ground. Also, the driver doesn't need to be very
symmetrical (LOW->HIGH performance can be different to
HIGH->LOW) because we can get away with different slew
rates on the LOW->HIGH and HIGH->LOW signal transitions.
If the two conductors are +Signal and -Signal, then the
driver needs two complementary drivers. The drivers need
to be very symmetrical, so that the LOW->HIGH on one line
corresponds very closely with the simultaneous HIGH->LOW on
the other.
The electrical characteristics (capacitance, inductance and
transmission line characteristic impedance) are also different
in each case, which can require different driver characteristics
to get optimum performance.
Later,
Kenn
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