RE: Separate +5V Plane

Grasso, Charles ([email protected])
Fri, 28 Mar 1997 08:55:26 -0700

Interesting discussion. The separation/segmentation of planes is a powerful
tool in achieving EMC. The original question was, I believe, whether or not
to segment 5V. The answer is a YES!!. If the 5V plane is not segmented in a
similar fashion to the ground, then essentially there is high frequency
capapcitance across the ground split thereby limiting its performance.

BTW. If you do not have file attachment capabilities on your E-Mail
service, one way to send graphics in a text format is to use MIME or

From: [email protected][SMTP:[email protected]]
Sent: Thursday, March 27, 1997 6:34 PM
To: [email protected]; [email protected]
Subject: Re: Separate +5V Plane

The last few years has seen a jump in techniques that out pace text books:
some of the benifits from techniques you discussed could be missed if you
take the literal context.

I keep a seperate ground for Digital circuits and Analogue circuits,
because it helps keep the emissions down. I design microcontrollers that
plastic cases and have to meet CISPER 22. Keeping micro, ASIC, FPGA and
memory switching noise away from my interface wiring is essential: having
common ground substantially raises the emissions. One area where I take
special care is where the A to D is. I cannot afford a 16 bit convertor, so
have a single slope integrator one implemented. The Comparator outputs are
located near the point where I tie A and D gnds together.

Providing seperate planes for each IC has been tried, but to only limited
succes in my case. I suspect that the nature of my traces prevents this
method from getting good results. Two chaps in MN have published papers on
this topic at the EMC Symposiums, and I'm sure I have copies somewhere. I
believe the term is "micro-island". If you need to know more I could try
dig them out.

Please let the list know how you go on.

Best regards,

Derek Walton.
L F Research EMC test facility

PS Anyone know of a good way to share graphics over the mailing list?
allow me to distribute some emission curves.