impedance

[blu at vl.com (Tom Metro)]

markw at mohawksoft.com wrote:
>> (he meant impedance, rather than inductance).
> 
> Actually no, pedant point here, however, and inductor has inductance. A
> cable (any wire, really) acts like an inductor.

It acts like a resistor and a capacitor as well, and thus impedance[1] 
is more accurately descriptive.


> In fact, impedance is not your problem in digital transmission, it is
> inductance. An inductor resists the change in current flow.

In fact the capacitance can be the greater barrier to high speed 
operation in many applications, particularly the examples you originally 
cited where the signaling was voltage, rather than current based. For 
example, RS232 cable length is limited by the cable capacitance[2].

I agree, for a current mode transmission, the inductive component of the 
impedance will be the limiting factor, though it appears that SATA uses 
voltage mode drivers.

  -Tom

1. http://en.wikipedia.org/wiki/Impedances
2. http://en.wikipedia.org/wiki/Serial_cable#Maximum_cable_lengths

-- 
Tom Metro
Venture Logic, Newton, MA, USA
"Enterprise solutions through open source."
Professional Profile: http://tmetro.venturelogic.com/

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.