[SI-LIST] Re: [Q] IR Drop - try this free demo software
- From: Cosmin Iorga <ci249534@xxxxxxxxx>
- To: Benjamin Kim <kdkim@xxxxxxxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Mon, 11 Oct 2010 16:59:38 -0700 (PDT)
Benjamin,
Besides the same distance the direction matters too. DC electric current lines
distribute within the plane following two rules:
1. They try to flow through the lowest resistive path, and
2. Parallel current lines repel each other.
The result is a current distribution within the plane similar to the magnetic
filed lines distribution of a magnet. If your current lines from VRM to
Sink(1A) overlap with the current lines to Sink(2A) on a given region of the
power plane then you need to add the overlapped current lines when applying
Ohm's law.
For multiple Sink/Source points this analysis becomes more complicated since
now
same direction current lines repel each other and opposite direction current
lines attract each other. The result is a 2-D distributed voltage drop across
the plane. If you are interested you can download the free demo of ChipQuake
Power Integrity Explorer software and play with the location of power/ground
(VDA/VSA) pins as sink/source points on the chip and see how the supply voltage
distribution changes across the chip (2-D map). This is for chip not PCB, but
the mechanisms of current flow are the same.
You can download thefree demo version of ChipQuake Power Integrity Explorer
from
NoiseCoupling.com ; http://www.noisecoupling.com (look for link on mid left
side
of home page). This is a limited functionality demo but it covers what I
suggested you to try.
Cosmin Iorga, Ph.D.
founder NoiseCoupling.com
http://www.noisecoupling.com
________________________________
From: Benjamin Kim <kdkim@xxxxxxxxxxxxxx>
To: Cosmin Iorga <ci249534@xxxxxxxxx>
Sent: Mon, October 11, 2010 4:13:04 PM
Subject: RE: [SI-LIST] Re: [Q] IR Drop
Dear Cosmin,
Thank you for your nice reply.
Now, I understand even if it is DC region, more voltage drop as current path
longer.
If so, I'd like to ask you one more question.
When all sinks are located at same distance from VRM,
There will be same voltage drop at each sink location.
But, I don't know what I can understand by using Ohm's law
if differenct amount of current flow for each sink.
Though that may be stupid question, I wonder how you think about it.
VRM-----Sink(1A)
VRM-----Sink(2A)
:Same distance from VRM
Thanks and Regards,
ê¹?기ë??(Benjamin Kim)
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
CMS Technologies
Sigrity Application Engineer
E-Mail : kdkim@xxxxxxxxxxxxxx
T +82-31-711-8290~3
F +82-31-711-8431
M +82-10-5262-4509
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
I'm not native. My meaning can be misunderstood.
If you have any question, please feel free to contact me.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Cosmin Iorga
Sent: Tuesday, October 12, 2010 1:40 AM
To: ê¹?기ë??; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: [Q] IR Drop
Benjamin,
This is not a surprise; you probably have shared impedance on your planes for
multiple current sinks. So look at the current flow path from VRM to each sink
location and identify the plane regions where these currents overlap. On these
overlapped sections you apply Ohm's law using the sum of corresponding sink
currents and your experiment will then make sense.
Cosmin Iorga, Ph.D.
founder NoiseCoupling.com
http://www.noisecoupling.com
________________________________
From: ê¹?기ë?? <kdkim@xxxxxxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Fri, October 8, 2010 4:02:43 AM
Subject: [SI-LIST] [Q] IR Drop
Dear all mentors,
I¡¯m beginner at SI/PI area based on microwave eng¡¯g.
Currently, I¡¯m doing simple example which have one voltage source(=3.3V)
and three current sink location.
Can anyone explain to me why IR drop amplitude is bigger at which smaller
sink current passes?
Stackup
------------ Signal02 VRM-----Sink(1A)-----Sink(2A)-----
Sink(1A) : Distance from VRM
------------ PlaneVSS 3.196V 3.189V
3.187V : IR Drop
------------ PlaneVCC
------------ Signal01
Thanks and Regards,
Benjamin Kim
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