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Jonathan Harris

ADC Noise: More on the Analog Inputs

Jonathan Harris
jonharris0
jonharris0
1/24/2014 9:12:07 AM
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Re: PCB layout impact
Hi Jayaraman, there isn't really an alternative action.  I realize that maybe I should clarify evena  bit further.  Symmetry must be maintained between the positve and negative analog inputs of each channel to the ADC.  The positive and negative of each input should be as symmetric as possible in layout. Assyemmtry will degrade even order distortion.  I was not referring to symmetry in layout between two or more channels in the ADC.  Of course, it is also good to keep symmetry between the channels but it will not affect the even order distortion of a given channel, it will just have an effect on the timing between the channels (delta would be based on the prop delay delta between the channels).  Hope this helps clarify a bit.

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JAYARAMAN KIRUTHI VASAN
JAYARAMAN KIRUTHI VASAN
1/24/2014 8:21:52 AM
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Master
Re: PCB layout impact
Jonathan Thx for the clarification. It would be great if you can discuss alternative action in case pcb symmetry in this regard is not possible.

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JAYARAMAN KIRUTHI VASAN
JAYARAMAN KIRUTHI VASAN
1/24/2014 8:21:44 AM
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Master
Re: PCB layout impact
Jonathan Thx for the clarification. It would be great if you can discuss alternative action in case pcb symmetry in this regard if not possible.

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jonharris0
jonharris0
1/24/2014 8:04:19 AM
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Re: PCB layout impact
Hi Jayaraman, that is exactly the assymmetry that I was referring to.  It is very important to keep the layout of the analog inputs to the ADC as symmetric as possible.  Thanks for the comment!

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JAYARAMAN KIRUTHI VASAN
JAYARAMAN KIRUTHI VASAN
1/23/2014 11:58:08 PM
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Master
PCB layout impact
Jonathan,

Nice post.

"Any asymmetry in the analog input network will lead to an increase in the even order distortion of the ADC."

I am curious to know the efffect of any asymmetry introduced by the PCB layout of the analog input network.

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More Blogs from Jonathan Harris
The topic of this blog came up while at the IMS show and one of my colleagues mentioned that I should discuss the ADIsimRF tool as a part of the series. I thought this was a marvelous idea. I’ll have to precursor this discussion with the fact that I am actually an RF guy from my previous employment at an RF company which was my first position when I graduated from college.
One of the questions that appeared on one of the IMS blog posts was about the details of the demonstration I had set up at the Analog Devices booth.
The last and final day of the show is usually has the most relaxed atmosphere and this year that proved to be the case once again. It is the shortest day of the show lasting from just 9:00 AM to 3:00 PM.
After having a pretty good first day of the show, I was looking forward to a good second day and it did not disappoint. The second day of the show on Wednesday is the longest day of the show as the exhibit hours go from 9:00 AM until 6:00 PM (day one is 9:00 AM to 5:00 PM and day three is 9:00 AM to 3:00 PM).
The IMS2015 show is already off to a great start here in sunny Phoenix, Arizona and I hope that those of you attending are enjoying it so far.
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