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This news has made AMD'ers happy



 
 
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  #61  
Old May 14th 04, 03:49 AM
Robert Redelmeier
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In comp.sys.ibm.pc.hardware.chips KR Williams wrote:
Please, "LC filters" aren't used for EMI reduction *AT ALL* in
this application. Al LC filter simply rings at its resonant
frequency, it doesn't attenuate anything. If you're thinking of
ferrite beads, they're not an 'L' at all. They're 'R's at the
frequency of interest. It takes an 'R' to dissipate power.
That's my point. There aren't LC circuits used to attenuate
anything, unless they're *REAL* morons. Perhap;s they can't pick
the right ferrite, but that's another issue (if they cannot even
follow the reference design...).


Well, maybe my terminology is off. I see three sets of "L"
components and "C" components on vidcards near the VGA connector.
They are most probably connected to the RGB analog output lines
and reduce the sharp corners, overshoot and high rise rate of
digital signals for analog transmission.

I don't buy it. The ferrite on the I/O won't help one iota if the
card is radiating elsewhere. Sure there are crappy designs, but
I'm not buying your LC filter theory. ...at least as stated.


Ah, but if the card is otherwise good, or nearly so, then
won't L & C omponents on the output stages help reduce EMI
from the monitor cable (aka antenna)?

-- Robert



  #62  
Old May 15th 04, 09:15 PM
KR Williams
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In article ,
lid says...
In comp.sys.ibm.pc.hardware.chips KR Williams wrote:
Please, "LC filters" aren't used for EMI reduction *AT ALL* in
this application. Al LC filter simply rings at its resonant
frequency, it doesn't attenuate anything. If you're thinking of
ferrite beads, they're not an 'L' at all. They're 'R's at the
frequency of interest. It takes an 'R' to dissipate power.
That's my point. There aren't LC circuits used to attenuate
anything, unless they're *REAL* morons. Perhap;s they can't pick
the right ferrite, but that's another issue (if they cannot even
follow the reference design...).


Well, maybe my terminology is off. I see three sets of "L"
components and "C" components on vidcards near the VGA connector.
They are most probably connected to the RGB analog output lines
and reduce the sharp corners, overshoot and high rise rate of
digital signals for analog transmission.

I don't buy it. The ferrite on the I/O won't help one iota if the
card is radiating elsewhere. Sure there are crappy designs, but
I'm not buying your LC filter theory. ...at least as stated.


Ah, but if the card is otherwise good, or nearly so, then
won't L & C omponents on the output stages help reduce EMI
from the monitor cable (aka antenna)?


No. You really want *resistors* there (ferrite beads are really
resistors at the frequency of interest). The idea is to absorb
the energy, not so much "filter" it. Who knows what silly
people do though. Lesse... opens G550 box ...nope no L's
there!

--
Keith
 




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