From: Tony Anthony (X2Y@X2Y.COM)
Date: Fri May 12 2000 - 13:33:39 PDT
I believe that you could filter the application you are talking about with
one component. I have recently tested a capacitor that filters common mode
and differential mode noise differentially (180 deg. out of phase ) and has
excellent attenuation characteristics. I compared that filter to other
filters and the results of that test (and the set up used) were published in
the April edition of Item 2000 Magazine.
I have a link to the article as well as an explanation of the basic
principles of the technology at www.x2y.com/FORSItestresults.htm. If you
decide you want to use this device, I need to have a better understanding of
your circuit and placement of the component.
X2Y Attenuators LLC
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org]On Behalf Of Spencer, David H
> Sent: Wednesday, May 10, 2000 9:12 AM
> To: 'email@example.com'
> Subject: [SI-LIST] : Reducing Power and Ground Noise
> Hi All,
> I'm working on a board currently which has "high" power and ground
> noise. I'm looking for effective methods of reducing this noise.
> I spent a bit of time making power and ground noise voltage measurement on
> the current configuration of this board. The results show that the power
> and ground system have noise spikes which are 180 deg. out of
> phase from an
> output clock on the board. I won't go into the measurement set
> up too much,
> but here are the basics:
> Using two FET probes to make the measurements. The ground
> reference was the
> digital ground input to the board. Scope was triggered off the suspect
> clock (64Mhz) .
> I suspect that an input filter to the device generating the
> signal (an ASIC)
> would improve things. I'm not sure about the correct
> configuration for this
> filter. Currently there are .1uF caps across each of the input power pin.
> I can think of two configurations that may be effective.
> A ferrite bead in series with each of the input power connections (keeping
> the .1uF caps) may be effective but I'm not sure what "side effects" may
> A inductor and resistor in parallel (also keeping the .1uF caps)
> setting the
> values .75uH and 5 ohms.
> I'm not sure what the draw backs of these configurations are. Or is there
> are better solutions.
> Additionally, I plan on decreasing the power and ground spacing (the board
> is a four layer) to 7mils, increasing the bulk capacitance to the
> board, and
> possibly placing .001uF caps in parallel with each of the .1uF caps.
> Any comments would be appreciated
> Best regards
> David Spencer
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