nport in Spectre

Hi,

I have an S-parameter file that needs to be included in my test bench.
This is a 4-port model. For some reason I don't know, the GUI nport
doesn't work so I borrowed such a small test bench from the manual
with slight modifications:

global gnd
simulator lang=spectre

model Sdata nport file="Sample.4port.data"

Port1 (i1 0) port num=1
TL1 (i1 0 o1 0) tline z0=25 f=1M
Port2 (o1 0) port num=2
Port3 (i2 0) port r=50 num=3
X1 (o2 0 o2 0) Sdata
Port4 (o2 0) port r=50 num=4

Op_Point dc
Sparams sp stop=0.3MHz lin=100 ports=[Port1 Port3 Port2 Port4]

But I still get errors

Error found by spectre during DC analysis `Op_Point'.
Matrix is singular (detected at `X1:t1').
No DC solution found (no convergence).

The values for those nodes that did not converge on the last Newton
iteration are given below. Also given is the manner in which the
convergence criteria were
not satisfied in the following form:
Failed test: | Value | > RelTol*Ref + AbsTol

How to use nport command in Spectre?

Thanks.

 

Well, for a start, if it's a 4 port s-parameter file, you've only specified 2
ports in the instance statement for the model Sdata. Often nport is used without
a model statement, but it should be OK doing what you're doing.
Each port is defined as pair of nodes (signal and reference, if you like).

Also, you've connected the two ports you have specified to be the same
(o2 connected to both).

Regards,

Andrew.