I need to translate a frequency band generated by a DDFS designed in a FPGA (using Xilinx DDS Compiler). My output to the NCO is in I/Q format. I chose to use a NCO to perform the frequency shift but I am wondering what is the best solution to do this:
- Is it better to define the frequency band generated by the DDFS around the center frequency 0 Hz and defining in the NCO the center frequency?
- Is it better to define the frequency band from 0 Hz and shifting it using the startband frequency?
In the DDS Compiler documentation, p.27, example 2 provides the way to describe negative frequency by using aliased positive frequency (Fs + (negative frequency)). But as these frequencies are high and close to Fs clock, will there be enough data points to correctly describe the signals for these frequencies?