I know this is a bit of a fundamental DSP question but I want to finally understand this and I think I need some help to finally put it all together.
Let's say I have an RF complex sampling ADC with a sample rate of 4GSPS. The device has built in decimation with a minimum decimation of 4X so my maximum capture bandwidth is 1GHz (I know slightly less to allow for aliasing guard bands etc.).
So I would put a 1GHz analog anti alias bandpass filter in front of the ADC to avoid any aliasing, and capture the full 1GHz bandwidth with the ADC. At this point I effectively have 4X oversampling and my data is output to the FPGA at 1000MSPS IQ samples.
The question I have is if I now want to break up this bandwidth in the digital domain into smaller pieces for simultaneous processing of different channels, lets say 100MHz chunks for simplicity.
Is that possible with decimation without breaking Nyquist rules? My analog anti alias filter is still 1GHz, it would seem like if I decimate by 40x to get the 100MHz bandwidth channels from the original samples that I would now have an effective sample rate of 100MSPS.
Does this work because the original data was taken with a higher sample rate and I am decimating and digital filtering non-aliased data?
I think that is the root of what i was getting at, would those filters need to be analog and limit the BW to half the final sample rate after decimation? The real question ends up being: is it possible to sample a wide-bandwidth (1GHz) and break it up digitally by digital filtering and decimating?