[SI-LIST] Re: Interpreting s-params to physical voltage levels.
- From: "Lakshmi N. Sundararajan - PTU" <lakshmi.s@xxxxxxxxxxx>
- To: <istvan.novak@xxxxxxx>
- Date: Sat, 6 Mar 2010 11:37:09 -0800
Hi Istvan,
Very nicely put.
I had forgotten the frequency dependency since I was looking at a single
s-param value within a range of freq where the s11 and s21 was at a max.
Now, given the frequency dependency, is there any way short of using a
spice tool, to see what would be the max attenuation for a given input
voltage level on this channel?
I assume that if the specs for this channel were to specify S11 and S21
for a given range of frequency for valid operation, then one can make a
judgement straight out of s-param values for the channel.
But otherwise, to make any sense of a s-param for a channel, is to see
the time domain graph for a given input signal.
And this can be made only using some spice tool.
I am curious at this point to understand, what other judgements can be
made straight out of s-param?
Thanks,
-LN
-----Original Message-----
From: Istvan Novak [mailto:istvan.novak@xxxxxxx]
Sent: Friday, March 05, 2010 9:16 PM
To: Lakshmi N. Sundararajan - PTU
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Interpreting s-params to physical voltage levels.
Hi Lakshmi,
This way of calculation would be limited to frequency-independent S
parameters, which they are definitely not. Keep in mind that in your
equations the S parameters are in the frequency domain, your voltages
are in the time domain.
Regards,
Istvan Novak
Oracle
Lakshmi N. Sundararajan - PTU wrote:
> Hi Gurus,
> Let us suppose I have s-param for a channel.
>
> I wanted to figure out from those s-param numbers, assuming I have a
1V
> input signal, how much would my receive signal magnitude be?
>
>
>
> Assuming, s-params are in decibels, then I figure the following
> definitions for each of them..
>
> Sxx_db = 20 Log (Sxx)
>
> Sxy_db = - 10 Log ((Sxy ^ 2)/(1 - Syy^2)) /* negative sign is
normally
> ignored since it is defined as loss */
>
>
>
> >From the above two equations, I can figure out Sxx and Sxy.
>
> And if I assume Vincident,x = 1V
>
> Then are the following equations correct?
>
> Vreflected,x = Sxx * Vincident,x
>
> Vinsertion,y = Sxy * Vincident,x
>
>
>
> If the above equations are correct, then I can translate manually from
a
> given set of s-params to a typical voltage levels to see the amount of
> attenutation,
>
> Magnitude wise on the channel, which is what I am looking for.
>
>
>
> Please correct me here in case my thinking is way off.
>
>
>
> Thanks,
>
> -LN
>
>
>
>
>
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