[SI-LIST] Fw: Re: why do I need mixed mode S parameters?
- From: axel stein <stein_axel@xxxxxxxxx>
- To: si-list <si-list@xxxxxxxxxxxxx>
- Date: Thu, 23 Dec 2010 06:49:06 -0800 (PST)
Hi Peter, Istvan,
yes, I made sure, that my port numbering is correct. I used the scheme, that is
at the very bottom of Jeff's email (port 1 and port 3 being the ports of the
differential pair on one end and port 2 and port 4 being the ports of the
differential pair at the other end).
I also made sure, that my unbalanced S-parameters were making sense. At low
frequencies, S21 and S43 were close to zero dB and S41 and S23 being below
-20dB.
One strange thing is, that if I separate all the unbalanced S-parameters in
real
and imaginary part (linear) and use the formula from Jeff separately for real
and imaginary, I end up in having the real part (or the imaginary part) of
Sdd21
already above 1 (amplified signal), which indicated to me already, that there
is
something wrong.
Any idea what could be wrong?
My Agilent PNA-X is saving the S-parameters in dB-angle format (angle should be
in degrees, not radians). I have converted the amplitude to linear by using
Sxx_lin = 10^(Sxx_dB / 20). The separation in real and imaginary was done by
multiplying with cos(angle) and sin(angle).
I can't find, where my blunder is, so any feedback would be greatly appreciated.
Best regards,
axel
--- On Wed, 12/22/10, Peter.Pupalaikis@xxxxxxxxxx <Peter.Pupalaikis@xxxxxxxxxx>
wrote:
>From: Peter.Pupalaikis@xxxxxxxxxx <Peter.Pupalaikis@xxxxxxxxxx>
>Subject: Re: [SI-LIST] Re: why do I need mixed mode S parameters?
>To: "axel stein" <stein_axel@xxxxxxxxx>
>Cc: si-list@xxxxxxxxxxxxx
>Date: Wednesday, December 22, 2010, 2:01 PM
>
>
>Hi Axel:
>
>I get S31-S41-S32+S42.
>
>The reason that this is different from Jeff's result is the port numbering
>(which is why doing this with formulas really stinks).
>
>Jeff's result seems to be for ports numbered:
>
>1 2
>3 4
>
>My formula is for ports numbered
>
>1 3
>2 4
>
>(where the left two numbers are the +/- singled ended ports that form mixed
>mode port 1 and the
>right two numbers are the +/- single ended ports that form mixed mode port
>2).
>
>
>You will need to verify your port numbering in order to get the correct
>results.
>
>Pete
>
>
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> |stein_axel@xxxxxxxxx
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>| Date: |
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> |12/22/2010 03:50 PM
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> |[SI-LIST] Re: why do I need mixed mode S parameters?
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>I have tried to use the formula from below to convert 4-port S-parameters
>to a
>SDD21 value. Unfortunately, the results was not even close to what my VNA
>would
>give me when directly displaying SDD21.
>
>What I did was:
>-measured the 4-port S-parameters --> results are available in dB-angle
>format.
>-I have converted the values first to linear-angle and then to linear_real
>-
>linear-imaginary format.
>-I have added / subracted the linear_real values according to the formula
>below.
>-I have added / subtracted the linear_imaginary values according to the
>formula
>below.
>-I converted the linear_real & linear_imaginary portions of the calculated
>SDD21
>back to linear-angle and finally dB-angle format.
>
>My expectating would have been, that the SDD21 values that I have
>calculated
>this way would be reasonably similar to the directly measured SDD21,
>however
>these two are showing significant differences.
>
>What have I missed here?
>
>Thanks for your kind help,
>axel
>
>___________________
>
>Loyer, Jeff wrote:
>
>>The formula that I know of is:
>>SDD21 = 1/2 (S21 - S41 - S23 + S43)
>>
>>For the reciprocal, symmetric system, S21 = S43, and S41 = S23. My
>>algebra says that, for this system, SDD21 = S21 - S41. I didn't check
>>your Maxim reference; please double-check it and let me know if it still
>>disagrees with the formula.
>>
>>Also, a quick Google search of "Pozar book" would've found the
>>information about that book - my thanks to Jeff of Agilent for providing
>>that info.
>>
>>Not to beat you up, but please invest a few ergs before responding
>>(especially to the entire list) - I invest a bit of time in my responses
>>(to keep from asking the obvious, mis-stating information, and/or
>>embarrassing my employer), and I appreciate others doing the same.
>>
>>Aside from that, I welcome folks letting me know if I've goofed and/or
>>asking for clarification.
>>
>>Jeff Loyer
>>
>>
>>-----Original Message-----
>>>
>>>For example, for the following circuit:
>>>p1 ------- p2
>>>p3 ------- p4
>>>
>
>
>
>
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