Re: [SI-LIST] : Terminator location with larger BGA's

About this list Date view Thread view Subject view Author view

From: Bob Lewandowski ([email protected])
Date: Fri Apr 07 2000 - 18:52:17 PDT


I agree, it's usually better to put a capacitive discontinuity (device input) across the line ahead of the termination than to put it at the end of a stub line beyond the termination. Capacitors at the
end of a stub get significantly enhanced (multiplied) by the line length of the stub. If you put the capacitive discontinuity on the line ahead of the termination you can make some effort to compensate
for it by raising the line impedance by narrowing before and after.

---Bob Lewandowski

Ron Miller wrote:

> A technique which though sub-optimal, helps is to run the traces through the
>
> chip pads and continue on to an open area, terminating there. What happens
> is you get a capacitve glitch on the TDR a few picoseconds before the term.
>
> ron miller
>
> > -----Original Message-----
> > From: [email protected]
> > Sent: Friday, April 07, 2000 1:17 PM
> > To: [email protected]
> > Subject: [SI-LIST] : Terminator location with larger BGA's
> >
> > We are using some 484 pin BGA's (FPGA's), which have edge rates of about
> > 170ps.
> > Using a series termination, it would have to be placed within 1/10 of the
> > transition length according to Howard Johnson. On FR4, the transition
> > length
> > would be .98, making the distance from source to termination .098. It is
> > not
> > possible to get all of the required termination's within that distance.
> >
> > Aside from slowing down the edges (not desirable), waiting longer for
> > things to
> > settle, or going with buried resistance, are there any other solutions for
> > placement of termination's? How are other people terminating large, high
> > pin
> > count devices?
> >
> > Thanks
> >
> > Bill McGiffin
> >
> >
> >
> > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > [email protected]. In the BODY of message put: UNSUBSCRIBE
> > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > ****
> >
>
> **** To unsubscribe from si-list or si-list-digest: send e-mail to [email protected]. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> si-list archives are accessible at http://www.qsl.net/wb6tpu
> ****

**** To unsubscribe from si-list or si-list-digest: send e-mail to [email protected]. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
****


About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Thu Apr 20 2000 - 11:36:06 PDT