This strategy uses a periodic reference signal to correct any upsets in the NCO accumulator. This strategy is appropriate for phased-array systems or other systems where the NCO phase must remain coherent with other system components.
- Program NCO_AR=1 to configure the accumulator to be reset on every synchronization event.
- Configure the NCO to use SYSREF as the synchronization source (NCO_SYNC_SRC=2). Program SPI_SYNC=1.
- Make sure the SYSREF generator is configured for continuous/periodic output.
- Since the accumulator is reset periodically, the
user must make sure that the programmed NCO frequency is an integer multiple of
the SYSREF frequency. Consider the frequency raster that the system requires
when choosing the SYSREF frequency.
- If the user cannot choose a SYSREF frequency that satisfies the frequency raster and is also a sub-harmonic of the multiframe/EMB frequency, then use the LSB of the JESD204C data stream to periodically synchronize the NCO. Use NCO_SYNC_SRC=3, and provide a periodic reference signal on the LSB of the I samples for DUC0.
- If any NCO accumulator or internal frequency register is upset, it is restored on the next synchronization event.