VGA and channel filter

[fanshuo]

normally, people put the channel filter in front of the VGA to get rid of the interference

but I found it is still possible to put the filter behind the VGA.

Any comparisons of the two choice?

 

[Mazz]

we are talking about receivers
The answer is in the noise vs linearity balance. The filter in front of VGA will relax the VGA linearity (infact the VGA will avoid the interference) but the filter noise have to be low.
Take into account that in modern receivers VGA and Filter are made by multiple stages like as:
VGA1- filter1-VGA2-filter2-VGA3-filter3 or the VGA is embedded inside the filter and the overall gain can be programmed in order to minimize noise or interference.
I hope it can help.
Mazz

 

[fanshuo]

I understand that either VGA or filter will have high requirement on its noise and linearity.

Mazz, can you give some reference on your mentioned

"VGA1- filter1-VGA2-filter2-VGA3-filter3" structure

Thanks!

 

[abcyin]

the filter before the VGA can relax the requirement of the linearity of the VGA, and the filter after the VGA is always for anti-aliasing before the ADC in the receiver system.
hope it helps!

 

[Mazz]

I'm not able to give you reference, sorry.
To better explain what I mean: both VGAs (or better PGAs, programmable gain amplifiers, that are step-VGAs) and filters are commonly made by multiple stages. If you design them putting one VGA stage and one filter stage (and so on) you can better control and balance noise vs linearity.
Mazz