AD9864 White Noise and Sampling Rate Questions

Hello,

Answers to your questions are as follows:

1)The white noise contribution is from the LNA/VGA/Mixer while the colored noise contribution is from the sigma delta ADC.  Operating with 24-bit  IQ data can reduce the colored noise contribution from ADC when operating with lower bandwidth signals.  Beyond 50 KHz of BW......not much difference exists between the Noise Figure for 16-bit vs 24-bit mode.   Operating with higher VGA settings causes the ADC's colored noise to dominate more.  Refer to figures 11-19 of datasheet.   

2) Note sure if you mean SSI clock rate vs the IQ rate.   The IQ rate is the ADC clock rate divided by the decimation factor.  Typically one should have the IQ rate be equal or greater than 2x the desired signal bandwidth.   The SSI clock rate can be equal to the ADC clock rate or divided down integer factor of it provided that that the SSI data frame can fit within the time period of the IQ data rate.