ADC12DJ3200EVM: I need to capture all the signals from 3GHz to 6GHz .

Hi seungyeon

The ADC EVM inputs will respond to signals from very low frequencies up to higher than 6 GHz.

When sampling at 6.4 GSPS (JMODE0 or JMODE1 at 3.2 GHz clock rate) the FFT plots the first Nyquist zone which is 0 to 3.2 GHz.

Any signals above 3.2 GHz will fold down into the first Nyquist zone. See this blog post for more information on that concept:

http://e2e.ti.com/blogs_/b/analogwire/archive/2015/07/22/rf-sampling-aliasing-can-be-your-friend

If you want to capture signals from 3 to 6 GHz, then you should change the clock frequency to 3 GHz so the sample rate is 6GSPS. Then the first Nyquist zone is from 0 to 3 GHz and the second Nyquist zone is from 3 to 6 GHz. Signals from 3 to 6 GHz will fold into the first Nyquist zone, folding around the Fs/2 frequency point, so the spectrum will be inverted compared to what it would look like in the second Nyquist zone.

If your signal source doesn't have any frequencies below 3 GHz or above 6 GHz your measurements should work OK. If these signals are present you will need to use low-pass and high-pass filters to block out those unwanted frequencies that are outside the second Nyquist zone.

Best regards,

Jim B