VGA -> ADC IF undersample: need of filter ?

[axcdd]

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.

 

[FvM]

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.

What do you mean with signal frequency? IF? Baseband?

 

[permute]

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

 

[axcdd]

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 ?

 

[FvM]

So putting bandpass between VGA and ADC makes sense to limit noise vga ?

Probably yes, if no passive bandpass filter in front of the ADC is involved in the design.