On the SNR slide, the Noise floor looks like it is around 100dB, so how is SNR 57dBc?
This is a great question, I had to look it up myself as I come from a low frequency background. SNR is the signal power compared to the noise power for a certain signal bandwidth. The noise floor power is typically the integration of all the noise within a given frequency bandwidth excluding the fundamental signal and its 6 harmonics. Which means that the larger the frequency bandwidth the worst the noise power is which translates into worst SNR. This is clearly shown by looking at the noise power equation: Pnoise = 10log(Pnoise) dB/Hz + 10log(BW) Hz. 10log(1GHz) is 90dB. So looking at the AD9625 example, the NSD at 1.25GHz is -149dB/Hz so the SNR = Psignal – Pnoise = -1 + 149 - 10log(1.25G)) ~ 57dBc. If the frequency bandwidth of interest is much lower than 1.25GHz, a LPF can be used to limit the bandwidth and in turn improve the SNR value.