Synchronize external LO with ZCU111

[arve9066]

Hi

I am looking to drive a PLL ( which acts as an LO for a mixer in my design) with a reference frequency from the ZCU111 board. Is there a 10MHz reference available in the ZCU111 evaluation board? I see 10-20MHz written right next to the SMAs J7 and J10, but am not able to find if this is indeed the right one? Can someone clarify? 

[klumsde]

Have a look at the diagram in ug1271. 

Figure 3-18

I think that you can take a ~10mhz reference clock out of the Lmk on j109.

I need to double check it.

It should be just a case of enabling it in the programming of the lmk 

Regards, 

Keith

[arve9066]

Thanks Keith ! 

Yes. I had noticed that before, but wasn't sure how to get it out. Is this detailed anywhere as a procedure? 

[klumsde]

Hi @arve9066

CLKOUT5 is on the LMK04028

You can turn this on in the TICSPRO tool and create a hex file for the system controller. 

It will give you a 12.8Mhz clock out on J108

i've attached the hex file it is just the same as the standard one that make a 122.88 clock for the LMX PLLs except it is outputting the 12.8Mhz clock to the SMA. 

Does this work for you???

[arve9066]

Thanks Keith!

The synthesizer requires a 10MHz reference.Is there a way to change the LMK to output a different frequency ? 

Also, is it better to use an external reference to phase lock the ZCU111 board or use the  12.8MHz external reference in the LMK04208 to phase lock the external synthesizer? 

[klumsde]

The RF pll can be programmed with a hex file from the TicsPro tool.

If you look in the gui you'll be able to see about changing the settings on the output dividers. It may be tricky to pick a setting that divides out to 10mhz.

Another option could be to provide an external 10mhz reference to the lmk. You can pull out a jumper and power off the oscillator and provide the reference externally. 

Keith

[klumsde]

To be more specific. 

You need to pull out jumper J110. 

This will power off the TCXO

Then you need to provide the clock from J109. 

You should look at the TICSPro tool to see what you can do with this 10Mhz reference you are proposing. 

[arve9066]

Thanks Keith ! That explains and clarifies a lot of things I downloaded the TICS Pro software and played with it a little. I found that by modifying the register R5 and having the clock divider for the clock out 5 at 307, I can get 10.006514MHz at ClkOut5 and with clock divider at 308 I get 9.970245. This the only number I am able to play with to get as close to 10MHz as possible, correct?

Also If I change the Internal VCO output from 3072MHz, the Clock out 5 frequency also will change? Or in otherwords, the 10 MHz I will get is only fixed relative to the internal VCO frequency. I am wondering if changing the ADC tile sampling frequency will change the ClkOut5 value also as well? My understanding is that it should not since that is decided by the LMX PLLs? 

Is the 122.88 MHz Xtal buffered output available from an SMA out that can be used?

[klumsde]

You've got to come up with settings that meet your needs in this case.

The lmk is a jitter cleaner so you are using it to create a set of clicks for the lmx 

You have to modify it such that you can provide a clock to the lmx and also give you this nice 10mhz reference you need

[arve9066]

Thanks! 

I got it. One final question. Is the TCXO frequency 12.8MHz or 122.88MHz? From the RF DC Evaluation GUI it is mentioned as 12.8MHz? 

[klumsde]

Hi @arve9066

In this case the TCXO is 12.8Mhz. Remember you have to option to pull out J110, this will power off the TCXO. you can then provide an external clock. Perhaps you could clock the LMK here with a 10Mhz clock from outside and then also use this clock to drive the IQ modulatr external LO.

[216673_rsp]

Hello,

I have been trying to sync the zcu111 board with external 10MHz reference clock from the signal generator.

I tried to feed this clock to the clkin1 input of the LMK04208 and configured the LMK04208 to generate 122.88MHz using the TICS PRO. Please find the image wrt this in the attachment.

Thinking that this way i could sync zcu111 clock generation with the external signal generator(which is used to feed the RF input for the ADC), I programmed the RFSoC with the generated files. But it didnot work out.

Any help in this regard will be highly appreciated.

Thanks

[ptrkrysik · Accepted solution]

I was struggling with the same problem of finding the right LMK04208 settings in TICS Pro in order to synchronize ZCU111 with 10 MHz external clock. Finally I've found them, but no one will give me back the time I lost on this. In order to spare others from loosing their time on solving this issue, I provide here a full guide. This, in my opinion, should have been done by Xilinx employees long time ago, as many of your customers need this feature. That is shown by numerous forum threads about this topic, that are left without conclusive solution.

Here is the description of what I had to do in order to synchronize ZCU111 with external 10 MHz clock reference signal:
1. Disconnect jumper J110 to disconnect power of 12.8 MHz TCXO that is connected to CLKin0 of LMK04208.
2. Connect 10 MHz clock reference to J109 SMA port on ZCU111.
3. Download TICS Pro (https://www.ti.com/tool/TICSPRO-SW).
4. Find and download LMK04208 and LMX2594 settings in tcs (TICS Pro) format proven to work with ZCU111 (to avoid solving two issues at once).
This wasn't easy, as it should have been. Finally I found them in rdf0476-zcu111-rf-dc-eval-tool-2019-2.zip file that can be found i.e. here:
https://www.xilinx.com/member/forms/download/design-license-xef.html?filename=rdf0476-zcu111-rf-dc-eval-tool-2019-2.zip)
They are located in rdf0476-zcu111-rf-dc-eval-tool-2019-2/GUI/Distribution_RF_DC_Evaluation_UI_1.5/Distribution_RF_DC_Evaluation_UI_1.5/Externals/Data/Clocking subdirectory.
The pair of files that I used was:
- 'LMK04208_ZCU111_revAB_CKin1=12M8_VCO=3072M_Out=122M88.tcs' - the LMK04208 config that needs to be edited,
- 'LM2594_0245M76.tcs' - some working LMX2594 config which won't be changed.
5. Edit the LMK04208 config file in TICS Pro:
- open TICS Pro and go to Select Device -> Clock Generator/Jitter Cleaner (Dual Loop) -> LMK04208,
- open 'LMK04208_ZCU111_revAB_CKin1=12M8_VCO=3072M_Out=122M88.tcs' file,
- change the settings marked with red rectangles on screenshot below:
  - disable EN_CLKin0,
  - enable EN_CLKin1,
  - set CLKin1 value to 10 MHz,
  - change 'Selected Clock Input for PLL1' to CLKin1,
  - set correct 'R Divider' (R) and 'N Divider' (N).

You can't change external VCXO frequency, which is 122.88 MHz. At least you can't without replacing it. However you can easily change R and N. What are correct R and N values? The R and N values control how PLL1 turns CLKin1 clock frequency to VCXO frequency:

N/R*CLKin1 = VCXO_freq

We need such N and R so:

N/R*10e6 = 122.88e6.

I don't know why on earth 122.88MHz frequency was chosen but it turns out LMK04208 is capable of turning 10 MHz into 122.88 MHz. The lowest R and N are:

R=125 N=1536.

They need to be set in 'R Divider' and 'N Divider' fields.

This is all what is needed. Now you can save the tcs file (it can be used in RF Data Converter GUI) or export LMK04208 and LMX2594 registers values (that can be used everywhere else).

I'm attaching the original LMK04208 config and one that was edited to turn J109 port into 10 MHz reference input ('LMK04208_122M88_ref_10M.tcs'). The settings are proven to work with 10 MHz  reference signal output from USRP.

Best Regards,
Piotr Krysik

[oriol.font]

Thanks a lot for this detailed answer @ptrkrysik! It is indeed a much needed feature for many of us.

If you don't mind, though, we'd like to make you another question related to using a 10 MHz external reference. In the user guide of the zcu111 (ug1271, pages 52-55) it is explicitly stated several times that in order to enable the use of an external reference you have to modify the board (i.e., desolder capacitors, etc.), with different modifcations being required depending on the means used to enter this reference (FMC, sysref SMAs, etc). Yet, from your answer, it seems that if we follow the procedure you describe and provide the reference clock from J109, then there is no need for any board modification at all. Is that correct?

Thank you very much in advance,

Oriol

[ptrkrysik]

@oriol.font, I've seen that part about the modification of capacitors and it was also confusing for me at first that it is requirement for external clock. But if you look at figure 3-18 from ug1271 the capacitors are directly in front of ADC/DAC clock inputs. You need to replace them only if you want to completely bypass LMK and LMX chips and provide your own clocks through Samtec LPAF 8x40 connectors (i.e. with use of  SMA inputs on XM500 card). To use the J109 input that feeds clock reference to LMK04208 ('SMA External Ref' on figure 3-18) no modification of elements on PCB is required.

[oriol.font]

Yes, I see that now. Thanks a lot!