[SI-LIST] A Hspice question about current on W-element
- From: "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 9 Apr 2008 10:15:31 -0600
Hi Zhen/Hassan,
First, I'm skeptical about the general ability of W-element to support =
two distinct ground nodes at its two sides. Remember that W-element is =
derived from telegrapher's equations where it was assumed the common =
ground. The model - as it was created internally - simply cannot support =
this mode, as long as it is important for you that in_gnd and out_gnd =
are different nodes.
Second, I disagree with the statement that if both in_gnd and out_gnd =
are connected to ground (are they indeed?) then their currents should be =
the same. There is no unambiguous definition of the 'node current'. =
There is a definition of the node voltage (potential) and the branch =
current. When we speak about currents, we need to define branches. I =
cannot reproduce your problem, but if I could run the simulator, I would =
connect the source and load through zero-value voltage sources and =
measured the currents through those sources. That is, measure the =
currents by external probes. The current balance you are seeking should =
immediately follow from current balance at the two 'input' and two =
'output' nodes, since they should have only single source or load branch =
connected. If it is not the case, look for the connectivity outside of =
the line, it may be improper.
Third, also terminology related: your W-element is four-terminal, but =
two port device (not the four port device as you call it). That means, =
the only voltages and currents you can hope to get right from this =
device are V(in, in_gnd), V(out, out_gnd) and the currents through the =
source and load branches. At this point, the allowed connectivity is the =
one where you can guarantee that the net current crossing the near/far =
end conductor + ground totals to zero. Some other connections are =
illegal. For example, the result of simulating:
W1 in gnd_in out gnd_out rlgcfile=3Dw1.rlgc L=3D1
V1 in out 1V
Rx gnd_in gnd_out 100
.connect gnd_in 0
is unpredictable, because the pairs of terminals (in, out) and (gnd_in, =
gnd_out) cannot be used as ports.
Vladimir
From: xuzhengrong <Zhengrong.Xu@xxxxxxxxxx>
Subject: [SI-LIST] =B4=F0=B8=B4: A Hspice question about current on =
W-element
Hassan,=20
Thanks for your reply.=20
I also paid attention to the problem.
As we expect, i3(W1)=3Di4(W1)=3Di1(W1) =3D-i2(W1) when the nodes of OUT =
and
OUT_GND is open.
But when the nodes of OUT and OUT_GND connect to an input buffer as a =
load,
still i3(W1)=3Di4(W1) i1(W1) =3D-i2(W1), and i3(W1) just has some =
transmission
delay to i1(W1) but has the same direction to i1(W1).
If IN_GND and OUT_GND both of that connect to 0 are thought as the =
same
node, why i4(W1) is not equal to i2(W1) or i3(W1) is not equal to =
i2(W1)
when i3(W1) has some transmission delay to i1(W1)?
How can I understand the current of the fourth node, i4(W1)?
=20
Best Regards,
Zhengrong
_____ =20
=B7=A2=BC=FE=C8=CB: Hassan O. Ali [mailto:hassan@xxxxxxxx]=20
=B7=A2=CB=CD=CA=B1=BC=E4: 2008=C4=EA4=D4=C28=C8=D5 20:25
=CA=D5=BC=FE=C8=CB: xuzhengrong
=D6=F7=CC=E2: Re: [SI-LIST] A Hspice question about current on W-element
=20
You said in_gnd and out_gnd both connect to 0 so it is the same node =
hence
expect same current that is directed in the opposite direction to the =
source
current i1(W1) and same direction to i3(W1).
Hassan.
On Tue 08/04/08 5:55 AM , xuzhengrong Zhengrong.Xu@xxxxxxxxxx sent:
Hi all,=20
I recently used Hspice to observe the current on a W-element.=20
W-element is a four-ports element as a distributed transmission line.=20
For example,=20
W1 in gnd_in out gnd_out rlgcfile=3Dw1.rlgc L=3D1, assuming that gnd_in=20
and gnd_out both connect to 0.=20
I used .print i1(W1) i2(W1) i3(W1) i4(W1) to observe corresponding i(in) =
i(gnd_in) i(out) i(gnd_out).=20
I(gnd_in) is the return current of i(in), so i(gnd_in) should be the =
inverse
phase of i(in). The same to i(out) and i(gnd_out).=20
The simulation results show that i1(W1)=3D - i2(W1) (as we have =
expected), but
i3(W1)=3D i4(W1) surprisingly.=20
Why is i4(W1) equal to i3(W1) instead of i4(W1)=3D-i3(W1) in this =
simulation?=20
Is anything wrong about my idea?=20
Appreciate anything about it.=20
Best Regards,=20
Zhengrong=20
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