Inphase (I) and Quadrature (Q) components of signals

--- Quote Start ---

For Fs/2 case I don't see how you can get sin/cos. You only get real frequency.

--- Quote End ---

Sorry, Kaz is right, I misread your 40MHz as the sampled bandwidth, rather than the sampling frequency.

If you are sampling a signal centered on 20MHz at 40MHz clock frequency, then you will likely have aliasing. So you have probably not understood how you need to sample your signal.

As shown in the slides, you can use a NCO at Fs/2 (1, -1, 1, -1, sequence) to flip sidebands, however, that would not apply in your case, since the signal would alias and be corrupted.

Cheers,

Dave