[SI-LIST] Re: Simulating s-parameter model in HSPICE - DC Data
- From: Jennifer Maharani <jennifer.maharani@xxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 14 May 2009 22:12:34 +0200
Hi Vladimir,
EM tools usually do not simulate at low freqs. Low freqs data are
usually generated by extrapolation. By having finer steps at low
frequencies, does really bring any help? Because the DC data is still
wrong.
Many thanks.
On May 14, 2009, at 9:27 PM, "Dmitriev-Zdorov, Vladimir"
<vladimir_dmitriev-zdorov@xxxxxxxxxx
> wrote:
>
> 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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