RFSoC Development Kit Getting Started Guide
Page 19
3.
Adjust the ADC tile clock to 1081.344 MHz. This controls the sampling rate for both RF-ADCs in the tile.
Figure 17 - Setting RF-ADC sampling rate
4.
The NCO frequency for the complex mixer within the digital downconverter represents the shift in frequency
to apply to the signal of interest at the ADC input, centered at F
c
in the analog domain. In this case F
c
= 1842
MHz for LTE Band-3. We wish to shift the CW tone at 1843 Mhz back to 1 MHz.
The complex mixer operates in the digital domain; NCO frequency settings in the range of -10 GHz to 10 GHz
translate to an 'effective’ NCO frequency in the digital domain (from -Fs/2 ... Fs/2). If the analog signal
centered at F
c
is in a higher Nyquist zone relative to the ADC sampling rate, a digital alias will be shifted back
to DC. This is sometimes referred to as sub-sampling, as described on page 48 of
Set the ADC complex mixer to -1842 MHz.
Figure 18 - Setting ADC complex mixer frequency
