[SI-LIST] Re: Effective Radius of Decoupling Capacitor
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 27 Aug 2013 02:21:34 -0700
There are a couple of different time/frequency dependent mechanisms: 1)
That arises due to the transmission delay between a power disturbance
and the capacitor, and 2) that arises from the frequency dependent
impedance of the capacitor.
1) If you consider a situation where a bypass capacitor is some distance
from a load, the capacitor itself cannot deliver charge to that load
faster than the round-trip transit time through the interconnect between
the capacitor and the load. For a capacitor to be effective at all its
impedance needs to be low compared to the load. A quarter wave
resonator translates a low impedance at one end: the capacitor to a
high impedance at the other end: the load. Therefore a given capacitor
placed 1/4 wavelength away from a load actually raises the impedance
seen by that load. For things with very fast edges this distance is an
issue.
2) Above the capacitor's SRF, a capacitor's impedance quickly becomes
inductive, and eventually the impedance rises linearly with frequency.
But just as important is the effective impedance and delay of the
interconnect, which is why we physically distribute bypass capacitors in
the first place. A fixed relationship such as radius = 1/(200 * 2pi
Fsrf) is an attempt to state a coarse distance away from the capacitor
where it will still appear capacitive. It is based on a presumption of
the interconnect characteristics and like any rule of thumb should be
used with caution.
Steve.
On 8/27/2013 12:52 AM, Jack Si wrote:
> Hi experts,
> I read from an application note that the effective radius of the capacitance
> if 0.005*lamda. lamda is the actual wavelength of the capacitor's resonance
> frequency.i.e, 2pi*vp*sqrt(LC). where vp is the propagation velocity. From
> this equation, i infer that the inductance(ESL) and capacitance are directly
> proportional in square root. i.e, radius increase with the increase of ESL or
> C.
>
>
> But in paper "Effective Decoupling Radius of Decoupling Capacitor" i found it
> is inversely proportional. Please suggest me where i miss the way.
>
>
> Thanks and Regards,
>
> Jack
>
> ------------------------------------------------------------------
> 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
>
>
>
--
Steve Weir
IPBLOX, LLC
1580 Grand Point Way
MS 34689
Reno, NV 89523-9998
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
All contents Copyright (c)2013 IPBLOX, LLC. All Rights Reserved.
This e-mail may contain confidential material.
If you are not the intended recipient, please destroy all records
and notify the sender.
------------------------------------------------------------------
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
Other related posts: