[SI-LIST] Re: Simulating s-parameter model in HSPICE - DC Data
- From: "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 14 May 2009 13:27:32 -0600
Neo,
Check what the sampling step is in your touchstone at low frequency. It
may well be the case that the time constant of your series capacitor is
large, (i.e. the lowest pass through frequency is low) and your sampled
dependence cannot adequately represent the transition from DC to this
low frequency because the step is too large. Then, it appears as if your
DC point is 'isolated' from the rest of your continuous data. If this is
the case, the touchstone should be re-sampled with finer step, to show
smooth transition from DC to higher freq. The base frequency should be
set accordingly.
Vladimir
--- On Thu, 5/14/09, Neo neoflash2008@xxxxxxxxx wrote:
From: Neo <neoflash2008@xxxxxxxxx>
Subject: [SI-LIST] Re: Simulating s-parameter model in HSPICE - DC Data
Point I
One thing I missed in the first post is that the simulated channel
contains AC coupling capacitors.
I think capacitor's DC response is open. The insertion loss is infinite.
The return loss is 0dB.
The tool might get fooled in such situation. The question is that how we
get rid of it? Simply taking away the DC data point seems working but
doesn't make me feel confident enough about the results.
Regards,
Neo
--- On Thu, 5/14/09, Beal, Weston <Weston_Beal@xxxxxxxxxx> wrote:
From: Beal, Weston <Weston_Beal@xxxxxxxxxx>
Subject: [SI-LIST] Re: Simulating s-parameter model in HSPICE - DC Data
Point Issue?
To: si-list@xxxxxxxxxxxxx
Date: Thursday, May 14, 2009, 4:08 PM
Neo,
I'm not the most expert on this topic, but I'll share what I know. Maybe
any wrong statements that I might make will prompt the real experts to
clarify my words. S-parameters are measured in the frequency domain.
When you use them to simulate a circuit in the time domain then the
simulator must transform the data from frequency to time. The process
should be simple in theory, but the data doesn't always fit the theory.
Most simulators use some kind of pole fitting algorithm to make a
time-domain simulation model from the frequency domain data. If your DC
data doesn't fit well into the pole fitting method, then it can cause
strange behavior. Also, some programs fit the magnitude of the data to
the poles and leave out the phase data. This can lead to time-domain
models that are non-causal. When you take out the DC data, which
apparently is inconsistent with the rest of the data, then the transform
algorithm is free to create a time-domain model that fits better to the
poles.
We could help you more specifically if you could share the S-parameter
data with us. I hope this short introduction gets you going in the right
direction.
Regards,
Weston
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