The SYSREF
signal is the timing reference for the system
and must therefore be handled correctly to ensure it does not degrade the
synchronization. This signal has the following requirements.
-
SYSREF
must be a high-quality, free-running, low-jitter signal, to allow it to be captured consistently by the analog sample clock. See the Zynq UltraScale+ RFSoC Data Sheet: DC and AC Switching Characteristics (DS926) for theSYSREF
requirements. - The
SYSREF
frequency must meet the following requirements:- If synchronizing RF-ADC and
RF-DAC tiles with different sample
frequencies, the frequency must be an integer submultiple of:
GCD(DAC_Sample_Rate/16, ADC_Sample_Rate/16)
-
SYSREF
must also be an integer submultiple of all PL clocks that sample it. This is to ensure the periodicSYSREF
is always sampled synchronously. - Less than 10 MHz.
- If synchronizing RF-ADC and
RF-DAC tiles with different sample
frequencies, the frequency must be an integer submultiple of:
-
SYSREF
must be safely captured by the PL, before passing to the core:- Setup/hold of
PL_SysRef
toPL_clock
must be handled as part of the user design. - Clock generation on the PCB can be used to facilitate this, if supported.
- Setup/hold of
- Analog
SYSREF
and PLSYSREF
must be the same frequency and have a constant phase relationship. If deterministic latency is required, the analogSYSREF
and PLSYSREF
must keep the same phase difference over reset to reset cycles. - For MTS synchronization, which covers both divider phase sync and
FIFO latency sync, the analog
SYSREF
and PLSYSREF
must be a continuous clock for the duration of the MTS procedure. It can be either AC-coupled or DC-coupled. TheSYSREF
signals can be shut down after the completion of the MTS procedure.Note: The signals should be turned on and stabilized prior to the MTS function call. - If analog
SYSREF
is being used to synchronize the phase of the DUC/DDC mixer NCOs across multiple AMD Zynq™ UltraScale+™ RFSoCs, then it must be DC-coupled with the ability to generate single or multiple pulse waveforms.