[SI-LIST] Re: RLGC matrix

The Req, Leq, etc. takes Bob back to the lumped domain. I think he's trying
to see the impact of media change from wire to trace, or trace to ball. In
this case, if you do calculate the sqrt(Lwire/Cwire), that'll be a huge
impedance since the wire will mostly have inductance, and a very small
capacitance.

When I was looking for an equivalent circuit, I even thought about running
analysis without wires, and then adding the wire as a separate Inductor,
even if I go with a "1nH per mm" kind of value.

The signal has to go through the different tunnels with different
transmission properties and some of it will have to reflect at every point
of change. So, I don't know if taking the average  value will take you where
you want.

My $0.02

Erhan



-----Original Message-----
From: Inmyung Song [mailto:imsong@xxxxxxxxxxxxxx]
Sent: Wednesday, January 23, 2002 8:07 PM
To: whizplayer@xxxxxxxxx; si_list
Subject: [SI-LIST] Re: RLGC matrix





-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On
Behalf Of Bob Patel
Sent: Wednesday, January 23, 2002 2:04 AM
To: si_list
Subject: [SI-LIST] RLGC matrix



Hi! I know this could be a dumb question but let me
put it out because somehow I am at loss in figuring it
out.
I have simulated a transmission line i.e. using the
stack up & trace dimensions to come up with the RLGC
matrix in HSPICE. Now, should I use Z =
sqrt(R+jwl/G+jwC) to calculate Z. And the R, L,C,G
values can be calculated by solving the individual
matrix in determinant form.

-> In case of low frequency or below 1GHz, the R and G is ignored to make it
simple.

The next question is can I calculate impedance in this
way for individual sections because I have three
sections: Driver( bond wire length) + trace 1(width =
9mil to achieve 34 ohm)+ Trace 2( width = 5mil to
achieve 50ohms).The overall impedance seen by the
driver has to be around 34 ohms but I know with the
values given above that it won't be so. Hence I am on
this path to calculate the impedance of each section
and then take the average to calculate Zeffective and
also the propagation delay.

-> You mean,
---------^^^-----()()()------------
              |            |
              >           |
              <          =
              >           |
              |            |
------------------------------------

   is equal with
 ---------^^^-----()()()---------------------^^^-----()()()-----------------
----^^^-----()()()------------
              |            |                     |            |
|            |
              >           |                     >           |
>            |
              <          =                     <          =
<            =
              >           |                     >           |
>            |
              |            |                     |            |
|            |
----------------------------------------------------------------------------
--------------------------------
How about using the summation for example, Req=R1+R2+R3, Leq=L1+L2+L3,
Ceq=C1+C2+C3, Geq=G1+G2+G3?
Then I think the Zeffective = sqrt(Req + jwLeq/Geq + jwCeq).


Thanks in advance
Bob

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