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AD9957 Multichip Sync with External Pulse

Question asked by doncas on Apr 3, 2013
Latest reply on Apr 24, 2013 by KennyG

I have been able to successfully sync two AD9957's on separate PC boards using the SYNC_OUT from one device as the SYNC_IN for the other device.  However, we would like to be able to sync both of the devices to an externally generated sync pulse.  Our sysclk=960Mhz and the external pulse we want to use is 75ns wide and has a period that can vary but is on the order of 1-20 ms.  The external pulse is not generated directly from the 960Mhz clock but is generated from a 160Mhz clock that is phase locked to the 960Mhz.


Using the external pulse as the SYNC-IN for both devices, I have NOT been able to obtain a successful set of setup/hold validation data.  The SYNC_SMP_ERROR bit is always set when I enable the sync timing validation function.  I have tried the validation sequence with the sync validation delay set to 1 and 2 but was unsuccessful.  In this external sync pulse configuration neither board is configured as the sync source.


Using an external sync pulse is mentioned in the AD9957 data sheet (see below).  Is there anything I need to do related to using an external SYNC_IN pulse in place of the AD9957 generated sync pulse that is not documented?  Any help would be appreciated.


"When a device other than another AD9957 provides the SYNC_IN signal it must be LVDS compatible. Furthermore, although SYNC_IN is typically considered to be a periodic clock signal, it is not an absolute requirement. It is feasible to drive the SYNC_IN pins with a single synchronization pulse as long as its edge transition meets the setup/hold timing required for the internally generated sync pulse (as detailed later in this section). "