FPGA output 2Mbit/s code stream based on FSK to AD9954, AD9954 internal clock is 400MHz, if baseband board and DDS has the same reference crystal, DDS output(100MHz) modulate spectrum is good, if not the same reference crystal, output spectrum is poor,DDS register is configured by MCU, and in addition, configuration is RAM segment and sweep mode to realize FSK modulation, output is not good ,too.
pls help analyze, thanks!