LMK04828: multi-board RFSOC

Hello,

I will get back to you tomorrow. 

Regards,

Will

Jingda, 

Nothing jumps out to me in your LMK04828 config.  Are you seeing synchronized outputs from the LMK04828?  

Regards,

Will

Hi Wiliam,

Due to the absence of a detection port for the sync signal on the clock board, I am unable to measure the sync output of the LMK04828. However, I can measure the phase difference between the two SDout1 outputs, which should be consistent with the sync output. I used VNC to measure the phase of the two 5M outputs. In trc1, a phase jitter of 5 degrees can be observed.

The following image shows the outputs of the LMX2594 on two different clock boards. It appears they are not aligned and have phase jitter.

Am I missing some configurations or using a wrong sync structure? As for LMX2594, our case falls under cat. 1. Should an external sync signal be needed for synchronization? However, when I enable sync mode(vco_phase_sync), the clock fails to lock.

Regards,

Jingda

Jingda, 

I will get back to you tomorrow.  Sorry for the delay. 

Regards,

Will

Hi Jinda, 

JINGDA LIU said:

As for LMX2594, our case falls under cat. 1. Should an external sync signal be needed for synchronization?

If operating LMX2594 in CAT1, External SYNC pulse is not required. 
If you set MUXOUT_LD_SEL to "Lock Detect" , the signal should be high if VCO has locked. 

Regards, 

Vicente 

Hi Prado,

Do you mean I need to disable the two sync signals provided by the LMK04828 to the 2594?

My case falls under the right side cat1. Does this mean I only need to select vco_phase_sync and do not need to provide an external Sync pulse signal?

Regards,

Jingda

Hi Jingda, 
If I'm not mistaken, you don't need to provide enable VCO_PHASE_SYNC but I can verify this tomorrow - I am not 100% certain but if I am correct I would agree with your statement, you will not require two SYNC signals from LMK. 
If the device is locked, I expect LD to be high. 

Regards, 

Vicente 

Hi Prado,

Thank you for your explanation. 

I currently have two clock evaluation boards, each containing one LMK04828 and two LMX2594. When testing two LMX2594 on the same evaluation board, the phases can be aligned. However, when measuring the LMX2594 from different evaluation boards, the phases cannot be aligned. I suspect this might be because the two LMK04828 are not properly synchronized.

Regards,

Jingda

Hi Jingda, 
After further research it appears for CAT1 SYNC, VCO_PHASE_EN must always be set, you will not require external PSYNC . All devices just need to share same reference clk source to maintain phase relationship. 
https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1174807/lmx2594-some-questions-about-category-for-sync-mode

You will need to ensure the outputs from LMK device that feed into LMX are phase aligned. If I'm not mistaken, there are two ways two do this:

1. Use an external SYNC to align outputs across the LMK devices. 

2 Utilizing ZDM (Zero delay mode) 

I will allow the apps engineer more familiar with the jitter cleaners to comment more on this though. 

Regards, 

Vicente 

Hi Prado,

To be honest, when I enabled this option, I observed that the output could not be locked.

If possible, could you provide a clock file template based on the .tcs file I provided earlier?

/cfs-file/__key/communityserver-discussions-components-files/48/LMX2594_5F00_500M_5F00_Ref_5F00_500M_5F00_Out_5F00_3000M.tcs

Thanks.

Regards,

Jingda

Hi Jinda, 
That is definitely odd. Assuming the outputs from the LMK device are stable you should be able to lock the VCO of the LMX device even if they're out of phase. 
In your config, PFD frequency is extremely low. Typically we want to make PFD as large as possible for optimal phase noise. 

I attached a revised config. Please note the issue with device not being to lock is separate from not having phase aligned outputs across devices. We first need to ensure devices locks beforehand. Once we manage to lock devices consistently we need to focus on having the reference clks from the LMK device being phase synced as they're fed into the LMX devices. 

I will let Will provide his input on the appropriate LMK configuration.

2867.LMX2594_500M_Ref_500M_Out_3000M.tcs

Regards, 

Vicente

Jingda,

vicente flores prado said:

1. Use an external SYNC to align outputs across the LMK devices. 

2 Utilizing ZDM (Zero delay mode) 

Vicente is correct, in order to sync all outputs you will need to trigger a SYNC to reset the output dividers.  Let me know if you need support in configuring this.  Zero Delay mode is useful for creating a deterministic phase relationship from the input to the output. 

Regards,

Will