[SI-LIST] AW: Re: SDD21 and SDD11
- From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
- To: "john lin" <johnlinc@xxxxxxxxx>, si-list <si-list@xxxxxxxxxxxxx>
- Date: Wed, 30 Nov 2011 12:09:58 +0000
Hi John,
There is a good chance that your signal will pass without problems even though
S11 is violated, but it isn't guaranteed by spec.
In the Spec you mention, S11 limit is mainly set to protect the transmitter
from strong reflections. If your transmitter has a higher reflection
acceptance, your violalting S11 might not be a problem as long as you stick to
that transmitter (i.e. no component changes for cost reduction...).
BTW: Did you check if the Reflections are caused by your DUT and not the probes
or other equipment? It sounds as if you took your data from measurements, and
an impedance mismatch right at the probing point can mess up your S11 figures
dramatically.
BR
Gert
-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
Auftrag von john lin
Gesendet: Mittwoch, 30. November 2011 11:16
An: si-list
Betreff: [SI-LIST] Re: SDD21 and SDD11
Hi Wolfgang,
Thank you for shedding your light on my questions.
The spec I talk about is IB, running QDR and FDR.
Masks are given for insertion loss and return loss.
Can I say to meet S21 shall be OK for signal transmission?
S11 is something related to EMI control, mentioned by Daniel Lai in his mail.
The masks are given in different purposes. S21 is necessary, but not S11.
or, are both "MUST"?
Thanks,
John Lin
2011/11/30 <Wolfgang.Maichen@xxxxxxxxxxxx>
> Hello John,
>
> keep in mind that for a loss-less transmission path (i.e. no energy
> absorbed, so anything that does not come out at the other end - S21 -
> must get reflected back - S11) energy conservation tells us that
>
> S11^2 + S21^2 = 1
>
> Or in other words, S11 = sqrt(1 - S11^2). Note that the formula takes
> the numbers as attenuation factors, not dB!
>
> S21 = -0.5dB = 0.944 gives a horrible S11 = 0.33 = -9.6dB.
> Even almost perfect S21 = -0.1dB = 0.989 still gives a relatively poor
> S11 = 0.15 = -16dB.
>
> Regards,
>
> Wolfgang
>
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of steve weir
> Sent: Wednesday, November 30, 2011 4:36 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: SDD21 and SDD11
>
> You can have passable Sx21 and still crummy Sx11. That is fairly
> common. You need to hunt down what is going on. It could be your
> measurement, or it could be you have a real problem with SDD11.
>
> Steve.
> On 11/29/2011 7:13 PM, john lin wrote:
> > Hi SI experts,
> > Could you please help to comment about I have a good SDD21,
> > insertion loss, but not a good SDD11, return loss?
> > Shall low insertion loss have a low return loss?
> > The total power shall include transmitted and reflected powers.
> >
> > From my recent S4P extraction for a differential pair about 3 inch
> > in length, I can see
> > SDD21 does meet spec. However, the SDD11 violates the spec, less than
> > -10dB.
> > will it be OK? Is the SDD21 our main concern?
> >
> > Thank you for your helps in advance.
> >
> > Best Regards,
> > John
> >
> >
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>
> --
> Steve Weir
> IPBLOX, LLC
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- » [SI-LIST] AW: Re: SDD21 and SDD11 - Havermann, Gert
