[SI-LIST] Re: Double-AC coupling

  • From: "Chen, Sherman" <sherman.chen@xxxxxxx>
  • To: "ilam.paridhi@xxxxxxxxx" <ilam.paridhi@xxxxxxxxx>, "balaseven@xxxxxxxxx" <balaseven@xxxxxxxxx>
  • Date: Thu, 13 Nov 2014 15:12:05 +0000

Yes, overly small coupling cap can cause droop on the DC component contained in 
the signal. Also, when the impd. of the coupling cap is large enough,  ISI will 
be generated due to both bandwidth limitation and reflection caused by the cap. 
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of I Ilamparidhi
Sent: Thursday, November 13, 2014 11:25 AM
To: balaseven@xxxxxxxxx
Cc: Venkat Pappu; si-list@xxxxxxxxxxxxx; Chris.Cotton@xxxxxxxxxxx
Subject: [SI-LIST] Re: Double-AC coupling

Hi,

Apart from discontinuity issues, having two ac-cap may also cause “DC wandering”



But the performance degradation highly depends on the data pattern i.e.
more precisely the amount of energy below the corner frequency. Generally the 
impact is very negligible on highly dc-balanced data like 8b/10b encoded.


Ilam

On Wed, Nov 12, 2014 at 11:39 AM, bala <balaseven@xxxxxxxxx> wrote:

> Hi All,
> What will happen if my serdes clock has two ac coupling capacitor.Does 
> this increase low frequency jitter?
>
> Regards
> bala
> On 12 Nov 2014 02:45, "Venkat Pappu" <ppreshu@xxxxxxxxx> wrote:
>
> > Depends on the Impedance of the cap at the data rate.
> > Location of the cap, it will be better if it is closer to the receiver.
> >
> > -Prashant
> >
> > On Tue, Nov 11, 2014 at 8:02 AM, Cotton, Chris 
> > <Chris.Cotton@xxxxxxxxxxx
> >
> > wrote:
> >
> >> You don't mention data rate but generally a link that runs 
> >> successfully with internal AC coupling will also run with 
> >> additional external AC coupling albeit with reduced margins. The 
> >> amount of reduced margin will depend on how much of a discontinuity 
> >> the external AC capacitors
> (including
> >> any additional vias or etch that me required to get the AC cap)
> presents.
> >>
> >> Chris
> >>
> >> -----Original Message-----
> >> From: si-list-bounce@xxxxxxxxxxxxx 
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx
> ]
> >> On Behalf Of bala
> >> Sent: Tuesday, November 11, 2014 2:02 AM
> >> To: si-list@xxxxxxxxxxxxx
> >> Subject: [SI-LIST] Double-AC coupling
> >>
> >> Hi,
> >> What will happen if a link has two set of AC coupling(internal as 
> >> well
> as
> >> external).
> >>
> >> I know this will reduce the total effective capacitance, does this 
> >> contribute to Link error?
> >>
> >> --
> >> bala
> >>
> >>
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--
Regards,
Ilam
Mobile No :  +65 86982621


" Any action that results in pain to self or others at present or in the
future, through body or mind - that is sinful action! "

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