It's not a "rule", it's a TDR observation. You don't notice the dip if the
edge is slow enough or the pad deviation is small enough. As for most things
in SI, "it depends".
-----Original Message-----
From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
Sent: Thursday, August 27, 2020 2:39 PM
To: olaney@xxxxxxxxx; shashankdatta1218@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: Cutout and Power reference for AC coupling
Capacitor
There is no impedance dip from this pad. This is a rule that is not founded
on good science. Much like our Covid program.
Lee Ritchey
Speeding Edge
P.O. Box 817
Bodega Bay, CA
94923
408-781-0253
I took the energy needed to be mad
And wrote some blues
Count Basie
Worry is like a rocking chair,
It keeps you busy, but doesn't get you anywhere.
Ross Ritchey
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf
Of Orin Laney
Sent: Wednesday, August 26, 2020 10:57 PM
To: shashankdatta1218@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Cutout and Power reference for AC coupling Capacitor
The purpose of the cutout is to minimize excess capacitance to ground and
the associated local impedance dip. This is only a problem if the cap is
wider than the trace. It doesn't matter much if L2 is assigned to ground or
power, since the power layer is at RF ground (to a first approximation) and
has the same effect. Another strategy is to use a cap that is the same width
as the trace or a little less. It acts like a continuation of the trace,
there is no impedance dip (to a first approximation), and you won't need (or
benefit from) a cutout. Tune your stackup to make the trace width compatible
with a standard cap size. For a coupling cap you can use one of the smaller
sizes. Just check that your manufacturing process can handle it. The
littlest ones are scary small.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf
Of Shashank D
Sent: Wednesday, August 26, 2020 9:27 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Cutout and Power reference for AC coupling Capacitor
Hi SI Experts,
Hope everyone is fine.
I have a doubt in providing Cutout for AC Coupling cap Pad to minimise
Impedance mismatch.
In my case, L1 is Cap placement, L2 is GND where i need to provide cutout
for Cap pad and L3 is Power layer.
So when i give Cutout in L2, Cap pad will have Power Ref in L3. Is it okay?
Or we need to change that to GND???
Kindly advise and do the needful.
Regards,
Shashank D
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
