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VGA -> ADC IF undersample: need of filter ?

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axcdd

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In my application I've got the VGA followed by 12-bit ADC (differential signal). System works with IF signal which is undersample in ADC. Should I include any lowpass filter between VGA and ADC? (VGA and ADC bandwith is 10x more then my signal frequency). I ask because in analog devices adcs datasheet is mentioned that there should be no shunt capacitors on differential signals in IF undersample systems - i just dont know why.
 

I presume a low-pass would attenuate the IF frequency and thus the sampled signal.

VGA and ADC bandwith is 10x more then my signal frequency.
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What do you mean with signal frequency? IF? Baseband?
 
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    axcdd

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For IF sampling -- also called bandpass sampling -- you would use a bandpass filter as the anti-aliasing filter.
 
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    axcdd

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My intermidiate frequency is 70MHz and VGA , ADC bandwidth is 800Mhz. ADC is driven by 56MHz clock if I recall correctly. So putting bandpass between VGA and ADC makes sense to limit noise vga ?
 

So putting bandpass between VGA and ADC makes sense to limit noise vga ?
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Probably yes, if no passive bandpass filter in front of the ADC is involved in the design.
 

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