From: Jim Muccioli ([email protected])
Date: Wed May 09 2001 - 11:08:38 PDT
Bhavesh,
I have a third approach. Eliminate the L-C filter because of its' narrow
frequency response and replace it with one X2Y component that is more effective
over a wider band.
That would require utilizing techniques published in this paper:
http://host9273.hostamerica.com/pdf_files/image_plane.pdf
Link to paper by Henry Ott, Robert German and Clayton Paul
This paper talks about techniques that utilize a reference plane for noise
reduction. The single X2Y four terminal device incorporates these principles by
providing attachments to your + and - lines and also parallel referencing the
high frequency return plane with the G1 and G2 terminations, which will reduce
via inductance. Of course all this is contingent on availability of a reference
plane.
We have been practicing these techniques filtering DC motors by substituting the
reference plane they propose with the metal shell of the motor housing. In doing
so, a single X2Y cap has replaced as many as seven other filter elements used to
help products meet EMI specs. This has been repeated with over 20 different
motor manufacturers we have worked with in the Automotive sector. These
companies have tried virtually every filter combination you can think of (L-C,
R-C, PI's, feedthru's) and they have yet to match our results using one device.
I presented these techniques at the recent EMC FEST 2001 in Detroit which can be
accessed at this link www.jastech-emc.com.
I have also reduced emissions on an automotive microprocessor board by providing
a reflective plane with a single X2Y attached (G1 and G2 terminations hooked to
the reflective plane) and the power leads attached to the A and B of the device.
This again significantly reduced emissions.
An interesting byproduct of conditioning both lines with one component that has
this internal reference, the internal line to line balance is 1-2.9% (inherent
in the mfg). That makes for very effective elimination of common mode noise.
Best Regards,
Jim Muccioli
X2Y Attenuators, LLC
www.x2y.com
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Michael Nudelman
Sent: Wednesday, May 09, 2001 8:09 AM
To: 'Patel, Bhavesh'; SI_LIST (E-mail)
Subject: RE: [SI-LIST] : Power filtering?
Bhavesh:
What we did (successfully) - we did not cut out planes; for PLL power we
just used two-pole LC filter (actually Ferrite-C and LC filter), and fat
trace around the chip. Right now we will do the experiment on the RC filter.
Mike.
-----Original Message-----
From: Patel, Bhavesh [mailto:[email protected]]
Sent: Tuesday, May 08, 2001 9:24 PM
To: SI_LIST (E-mail)
Subject: [SI-LIST] : Power filtering?
Hi! Gurus, I had a question regarding the amount of noise rejection that can
be achieved 1)by using a filter 2) using separate power plane.
If the IC manufacturer said that the PLL power to be supplied has to be
'clean' then he is mentioning about the noise rejection that he would like
to have on these power pins that feed power to his internal PLL's.
The manufacturer will typically recommend an RC filter and I believe the IC
mfgr has verified on his test board that this the filter values that will
achieve the noise rejection.
Now, some designers want to cut up the power plane i.e. say from the main
3.3V plane cut up a small portion use the Resistor as a bridge to feed the
power to the island.
I believe we have achieved two levels of rejection 1)filter 2) cut up plane.
Can I just use the filter and not cut up the power plane and if I have to
how do I calculate the noise rejection number by using the filter & using
the island approach.
Thanks in advance
Bhavesh Patel
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