[SI-LIST] : Transmission Line Thy Applied to short interconnects

greg kimball (gkimball@indra.com)
Thu, 18 Mar 1999 08:34:59 -0800

I have a short, but important differential interconnect on a 100 ohm
flex
circuit with a rise time of 1ns and a two-way prop delay of 0.5ns.
My load is a inductive recording head(45nH). My driver is a H-Bridge
current
driver(During the rise/fall times it is complex impedance from
capacitance
effects). My goal is fastest current rise/fall times with overshoot
control.

My knotty question concerns the possible application of transmission
line
theory to this domain of SHORT interconnect length in relation to the
rise
time, unterminatable load, and 'current source' complex Z driver.

This configuration may not be the optimum for my requirements and am
looking
to optimize both the single-layer interconnect Zo and the driver(which
must end
up to be a current driver after the rise/fall time transitions).

One as aspect is reflections and the other is optimum current rise time
in
the head.

Reflections:
Since I will have two down and back reflections from my 'high impedance'
load (during the rise/fall times)with diminishing intensity, i probably
will not
even see reflection effects??? (so i don't need be concerned about
matching?)

Fast current transmission:
Will classical transmission line theory apply here - to the rise/fall
domain?
'If source or load is terminated in Zo of the line, a lossless line
looks
purely resistive'. Therefore, make the current driver look like Zo
during
the transitions,and like a current source thereafter.

Is this 'hybrid' approach the optimum ??
Am i now not concerned so much about longer interconnects,
since i am matched during the critical timeframe??

Thanks and regards,
Greg Kimball
Applications Engr
TI Storage Products GP

**** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****