[SI-LIST] Re: .NET Statements in HSPICE for S-Parameters
- From: Ross Jatou <RJatou@xxxxxxxxxx>
- To: "'cmlin@xxxxxxxxxxx'" <cmlin@xxxxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Fri, 10 May 2002 14:20:49 -0700
Remove the Rx of 50 Ohms and you should be ok. A quick way to solve this is
by making 50 --->50000.
By having the 50 ohms on the load only, you are double terminating one side.
______________________________________________
Ross Jatou
Senior Manager, PCB Design Methodology
Tel. 408-486-2841 Fax 408-486-4841
Nvidia corporation
2701 San Tomas Expwy., Santa Clara, CA 95050
-----Original Message-----
From: Chien-Min Lin [mailto:cmlin@xxxxxxxxxxx]
Sent: Friday, May 10, 2002 2:02 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] .NET Statements in HSPICE for S-Parameters
Hi, Dear All,
In reference to
David M. Pozar, Mircowave Engineering, 1990 on Page 223:
Find S-parameters of the 3dB attenuator circuit --
o---(8.56ohms)--o--(8.56ohms)-----o
|
Port 1 ==> (141.8ohms) <== Port 2
|
o--------------GND----------------o
the S parameters are given by: S11 = 0 and S21 = 0.707.
In use of HSPICE 2001.4, here is its equivanent .sp script:
*********************************************************************
* David M. Pozar, Microwave Engineering, 1990: Page 223
* Also, Reference: HSPICE 2001.4 User Guide: Page 12-17
*********************************************************************
.OPTION Post
+ DCSTEP=1
*--[ 3dB Attenuator]------------------------------------------------*
*
* IN---[R1]---A---[R2]---OUT---[Rx]
* | | |
* [Vin] [Rc] 0
* | |
* 0 0
*-------------------------------------------------------------------*
Vin IN 0 AC 1
R1 IN A 8.560
R2 A OUT 8.560
Rc A 0 141.800
Rx OUT 0 50.000
*-------------------------------------------------------------------*
.AC lin 30000 0 3000Meg
.NET V(OUT) Vin Rout=50 Rin=50
.plot AC S11 S11(dB) (-50,10) S11(P) (-180,180)
.plot AC S21 S21(dB) (-50,10) S21(P) (-180,180)
*-------------------------------------------------------------------*
.END
*********************************************************************
The simulation results are | S11 | = 166.9m and
| S21 | = 471.8m
Nonetheless, the analytical solution would be
S11 = V1-/V1+ = (Zin - Zo) / (Zin + Zo) = 0 (matched)
ZB Rx
S21 = V2-/V1+ = --------- x --------- = 0.707
ZB + R1 R1 + Rx
where ZB = Rc // (R2 + Rx) = 41.444
Would you all please comment on the simulation results?
Meanwhile, how to probe the AC analyses for V1-, V1+, and
V2-? Is there something wrong with the .NET statement in
the .sp script? Is it needed to put a source resistor in
series with Vin s.t.
Vin IN 0 AC 1
Rs IN S 50.000
R1 S A 8.560
R2 A OUT 8.560
Rc A 0 141.800
Rx OUT 0 50.000
(It turns out: | S11 | = 263.07m and | S21 | = 297.95m)
Appreciate so much for all your comment and assistance.
- Jamie
.AC lin 30000 0 3000Meg
.NET V(0) Vin Rout=50 Rin=50
.plot AC S11 S11(dB) (-50,10) S11(P) (-180,180)
.plot AC S21 S21(dB) (-50,10) S21(P) (-180,180)
.plot AC Zin(M) (5,130) Zin(P) (-90,90)
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