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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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Blogger
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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Blogger
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
User Rank
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
After looking at the performance metrics in the online ADC simulator tool it is a great time to look at another online ADC tool called the Frequency Folding Tool. It is a useful simulator that helps to understand the effects of aliasing in an ADC.
. I received a very good reader question from my last blog post regarding the various parameters that are reported by the tool. Letís take a look at an example and explore the parameters that are returned. In this example we will look at the AD9643-250.
Now letís look at the web-based evaluation tool. This does not require downloaded software to run as it is purely ran from the web
First, to make any ADC operate we need to set up the input stimuli.
We begin this series of blogs by taking a look at ADIsimADC, which is a quite relevant design tool for Jonathan Harris, an applications engineer in ADI's high-speed ADC group.
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