LMX2820: LMX2820 frequency hopping phase synchronization

do you have any other LMX device that can support the automatic re-sync for the frequency hopping?

if we skip VCO calibration, will it still need manual recalibration? If so, how fast the re-calibration takes? I would like to estimate the total time including settling time plus calibration. I can manage the settling time to <20usec by adjusting loop filter BW but re-calibration time is uncertain.

Hi Youngho,

Currently we don't have any part support auto-resynchronization. 

In your last post, did you mean VCO re-calibration but not phase resynchronization? If you use instant calibration, there is no "VCO calibration" at all, it will take a couple of micro-seconds for the PLL to settle down to the new frequency. Phase synchronization, however, may take hundreds of micro-seconds.

Youngho,

Can we be more specific about what automatic resynchronization is?

Toggling the SYNC pin with FCAL_EN=1 will trigger a re-calibration if you are using standard calibration, so in this sense, you can combine VCO calibration with SYNC, but standard VCO calibration is much slower.

LMX2820 has instant calibration, so this is much faster.  LMX2820 has shadow registers as well, so I'm not sure how this works.

About the time, we have to make sure that there is no cycle slipping when the final divider is engaged, so the calibration time is dominated by MASH_RST_COUNT

So if you are using the output divider, we can not synchronize this until we know that the PLL is settled enough that there is no cycle slipping.

Regards,

Dean

Dear Dean,

Thank you for responding this thread. About automatic re-synchronization, In frequency hopping systems, the challenge is resynchronizing the multiple devices after changing frequency. This causes a dead time in operation and also causes process load on the controller. ADF4368 provides automatic resynchronization feature.  This means any frequency changes are automatically synchronized and no additional synchronization request is needed. ADF4308 is a good candidate for that purpose but did not show any lock time plus synch time. So, if TI's part can offer those features for hopping, that will be very helpful.

Best,

Youngho

Hi Youngho,

Thanks for the clarification. Noel is out on travel but will assist you when he is available.

Best,

Evan Su

Noel,

For LMX2820, what is the best way to re-sync multiple devices for frequency hopping if this is possible with external trigger. What would be the total settling time would be including this re-sync? Do you have any information about it? Or, do you have any other product that enables multi-device re-sync over hopping?

Thank you. 

Hi Youngho,

Noel will get back to you next week.

Best,

Evan Su