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Old 9th May 2002, 05:25 AM   #11
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Default On shakey ground

Go for the solid ground plane And good decoupling for the digital power pins like 0.1uF SMD ceramics. This is a very complicated subject even among RFI and digital engineers. Getting the noise coupled into a good ground plane will help minimize to need to isolate it from analog circuitry. Dr. Johnson's book and the www.sigcon.com website will give you the most insight into this subject as well as ap notes on mixed signal design at the major semiconductor sites like www.analog.com I spent two years working on a two layer digital analog telecom line card and a large part of that was on grounding and decoupling.

H.H.
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Old 9th May 2002, 05:37 AM   #12
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Default Radiation........

Yes, indeed..........

But that is why you bypass all connections in/out of the enclosure.

Jocko
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Old 9th May 2002, 05:59 AM   #13
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Wink Radiation

You hear the most outrageous lies about it. Half-baked goggle-boxed do-gooders telling everybody itís bad for you. Pernicious nonsense! Don't forget to seal the trunk of your'64 Chevy Malibu!

H.H. (Hot and Hazardous Helping hand)

Harry Dean Haller
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Old 9th May 2002, 11:04 AM   #14
sonnya is offline sonnya  Denmark
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Default split versus not split

You could use the split thing to some level.

Example :

Your PLL for the DIR1701/1703. You have 3 pins : AVDD (pin 24),AGND (pin 23) and FILT(pin 22).

Your DGND is placed on (pin 6).

Then look at the image. It is not split up that much. Normaly you would take you AVDD from your DVDD through a filter (ferritbead, RC filter ... )

Sonny

PS : I forgot to say that this is a way of prevent digital current loops flow through the PLL filter wich is your ciruit needed to make a stable and jitter "free" clock. This is not possible when you do not make such thing to you PCB design.
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Old 9th May 2002, 02:11 PM   #15
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Default Fun with Groundplanes

Read the notes at www.analog.com on the AD8307 logarithmic converter. If you don't ground this baby correctly you can have a very nice wide band receiver (with great dynamic range!). I liked the comment on www.sigcon with respect to fixing a groundplane problem -- if you are succesful this becomes your job description. I also read on one of the analog sites the tale of finding emi problems by using an inexpensive (aka very cheap) a.m. radio and passing it over the circuit to find the offending elements.
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Old 9th May 2002, 07:29 PM   #16
tiroth is offline tiroth  United States
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An article which addresses multiple ICs requiring quiet grounds:

http://www.sigcon.com/articles/edn/multipleadc.htm

I am planning on going with the "multiple moat" approach and use differential outputs, avoiding any reference to chassis (or external) ground.

Does this change your single-ground recommendation Harry?

Your bypassing note is well taken Jocko.
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Old 10th May 2002, 01:55 AM   #17
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Did a CD player mod......about 12 years ago with a ground plane. Radiated like mad. Mainly from the analog output jacks.

Jocko
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Old 10th May 2002, 02:26 AM   #18
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Default Ground plane

A ground plane is the most effective grounding schema for digital circuits in terms of low noise coupling and low EMI. Nothing I have ever read of measured has shown me any reason to believe otherwise. I did EMI reduction as part of my last three jobs and gave a lecture to 150 people on the subject. For a list of good books:

http://www.emiguru.com/bibliog.htm

The following are the best that I have read and are the standard references that I have seen on many engineers bookshelves.

"EMC and the Printed Circuit Board," Mark Montrose, IEEE Press, 1999

"High-Speed Digital Design," Howard W Johnson and Martin Graham, PTR Prentice Hall, 1993

"Introduction to Electromagnetic Compatibility," Clayton Paul, John Wiley & Sons, 1992.

"Noise Reduction Techniques in Electronic Systems," Henry W. Ott, John Wiley & Sons, 1988

H.H.
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Old 10th May 2002, 04:58 AM   #19
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On the CD player mod, it was necessary to put a cap (few hundred pF) from the output to the ground on the RCA, then put a 0.1 uF from the RCA ground to the chassis ground. With short leads. EMI gone. The analog ground leads acted like a good antenna.

Jocko
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Old 10th October 2002, 05:49 PM   #20
kenev is offline kenev  Greece
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I' m in the process of designing a PCB (double sided) for a TDA1541 non-oversampling DAC, which will be driven directly from the I2S output of my CD-PRO2 drive. Actually, the DAC will use two TDA1541 dac chips in parallel.
Reading the posts in this thread, the following question arose: should I use a single or dual (A + D) ground plane? The board will not include other chips except the two TDA1541 dac chips. According to the posts, the dac chip should be considered as analog part and should rest entirely on the analog ground plane. But, on the other hand, this chip has already two seperate ground pins, one analog and one digital ground. If the designer of the chip chose to have two different ground pins, why should I consider them as a single ground point?
So,which way to go, single or double ground plane?
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