[SI-LIST] Re: .NET Statements in HSPICE for S-Parameters
- From: Yu Liu <yu_liu@xxxxxxxxxxxxx>
- To: cmlin@xxxxxxxxxxx
- Date: Tue, 14 May 2002 21:00:57 -0700
Chien-Min,
As far as I know, S-parameter is a port concept. So it creates confusion if
you try to think it as a node concept. However, you can generate
S-parameters
using the .net statement for a circuit node, but the generated
S-parameters are
essentially the same for the two cases you described. Physically
speaking they
are different, but from .net statement point of view, they are equivalent.
As for the S-parameter relations for the cascade networks, I can't find
a simple
relation. There is a straight-forward relation of ABCD matrix for cascaded
networks, and the transform between S-parameter and ABCD matrix. But is
there a
simple relation formula to give out cascaded network's S-parameter,
based on each
subnetwork's S-parameter?
Yu
==
Chien-Min Lin wrote:
>
>Appreciate very much for the subtle comment of Ross.
>Now, it did work as expected in the analytical one.
>To extend the study in S-parameters, the .sp script
>is provided for a typical transmission line network
>with some stubs:
>
> IN---[Tx1]---n1---[Tx2]---n2---[Tx3]---n3---[Tx4]---OUT
> | | | | |
> | | | | [Rd]
>[Vin] [Sb1] [Sb2] [Sb3] |
> | | | | 0
> 0 0 0 0
>
>
>(00) S-Parameters / .NET
>*********************************************************************
>.OPTION Post
> + DCSTEP=1
>*--[ Transmission Line (W element): XFX ]---------------------------*
>
>.subckt nom_W4x1 1 2 3 4 Len_in=10
> $: Er=4.0 Zo =49.89 TD =2.03 num_sig=1 h1=4.65347 h2=4.9505 w=4
> W1 1 2 3 4 Umodel=umod N=1 L=Len_in
>.model umod U Level=3 NL=1 Elev=2 Llev=0 Plev=1 Nlay=2
> + L11=8.453n
> +
> + Cr1=3.397p
> +
> + R1c=0.252
> +
> + Gr1=0
> +
> + R1s=2.90989e-05
>.ends nom_W4x1
>
>*--[ Two-Port Network: Tx + Stub ]----------------------------------*
>*
>* IN---[Tx1]---n1---[Tx2]---n2---[Tx3]---n3---[Tx4]---OUT
>* | | | | |
>* | | | | [Rd]
>* [Vin] [Sb1] [Sb2] [Sb3] |
>* | | | | 0
>* 0 0 0 0
>*-------------------------------------------------------------------*
>
> Vin IN 0 AC 1.0 $: exciation
>
> X_Tx1 IN 0 n1 0 nom_W4x1 Len_in=1.0 $: unit = inch
> X_Tx2 n1 0 n2 0 nom_W4x1 Len_in=1.0
> X_Tx3 n2 0 n3 0 nom_W4x1 Len_in=1.0
> X_Tx4 n3 0 OUT 0 nom_W4x1 Len_in=1.0
>
> X_Sb1 n1 0 0 0 nom_W4x1 Len_in=0.2
> X_Sb2 n2 0 0 0 nom_W4x1 Len_in=0.2
> X_Sb3 n3 0 0 0 nom_W4x1 Len_in=0.2
>
> Rd OUT 0 1E14 $: open load
>
>*-------------------------------------------------------------------*
>.AC dec 500 1 8500Meg
>
>.NET V(OUT) Vin Rout=50.0 Rin=50.0
>
>.probe AC S11 S11(dB) (-50,10) S11(p) (-180, 180)
>.probe AC S21 S21(dB) (-50,10) S21(p) (-180, 180)
>*-------------------------------------------------------------------*
>.END
>*********************************************************************
>
>
>In brief, the S11 and S21 are referred to
> _________
> V1+ | | V2+
> --> | 2-Port | <--
> Vin o-------+ +-------o Vout
> <-- | Network | -->
> V1- |_________| V2-
>
>that is,
> S11 = V1-/V1+ while V2+ = 0
> S21 = V2+/V1+ while V2+ = 0
>
>Nonetheless, is there well defined for S11_ni and S21_ni
>as depicted in the branched network?
>
> IN---[Tx1]---n1---[Tx2]---n2---[Tx3]---n3---[Tx4]---OUT
> | | | | |
> | | | | [Rd]
>[Vin] [Sb1] [Sb2] [Sb3] |
> | | | | 0
> 0 0 0 0
>
>That is, at Node n1: S11=? S21=?
> n2: S11=? S21=?
> n3: S11=? S21=?
>
>Can the .NET statements be applied in the .alt statements:
>
>.alt (01) .NET V(n1) Vin Rout=50.0 Rin=50.0
> .NET V(n1) Vin Rout=50.0 Rin=50.0
> .probe AC S11 S21 $: node n1
>
>.alt (02) .NET V(n2) Vin Rout=50.0 Rin=50.0
> .NET V(n2) Vin Rout=50.0 Rin=50.0
> .probe AC S11 S21 $: node n2
>
>.alt (03) .NET V(n3) Vin Rout=50.0 Rin=50.0
> .NET V(n3) Vin Rout=50.0 Rin=50.0
> .probe AC S11 S21 $: node n3
>
>
>However, it confuses me with my understanding in the 2-port
>network. For instance, at the node n2:
>
> IN---[Tx1]---n1---[Tx2]---n2---[Tx3]---n3---[Tx4]---OUT
> | | | | |
> | | | +----> | [Rd]
>[Vin] [Sb1] [Sb2] | [Sb3] |
> | | | | | 0
> 0 0 0 | 0
> |
> |
> at n2: look into an open end
>
>is it needed to break/remove [Tx3... to the right of n2] by
>terminating at 500000ohms:
>
> IN---[Tx1]---n1---[Tx2]---n2---+[50000ohms]
> | | |
> | | |
>[Vin] [Sb1] [Sb2]
> | | |
> 0 0 0
>
>such that
> .NET V(n2) Vin Rout=50.0 Rin=50.0
>
>can be applied to calculate S11 and S21 at n2?
>
>What is the difference in physics between these two models:
>without removing [Tx3...] and 50000ohms terminated at n2?
>
>Thanks for all your sophisticated advice, indeed.
>
>
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