DWM3000 Clock Distribution

Hi All,

I’m building clock distribution system with four DWM3000 modules.
Trying leverage ideas decribed in
Clock distribution issues - #5 by mciholas related DW1000 device.
The DWM3000 module does not have external clock input and I did some rework on module, removing original XTAL and caps and connecting external clock directly to XTI H15 ball through 2200pF series capacitor.

Please see full setup diagram attached.
DW3000 Clock Distribution.pdf (299.2 KB)
We didn’t test the system yet and asking your review based on scematics and oscopes shots included.
Do you see anything wrong - clock signal quality and swing at H15 ball and G14 output?

I started to power PL135-47OC from 1.8V LDO to reduce swing of output clock, but found quality of clock across all clock distribution path worse compared with 2.5V LDO I used.
Is any restriction on DW3000 XTI clock level as it was decribed for DW1000?

I see clock DC offset at XTI pin. Is any additional termination or DC biasing required at XTI H15 ball?

The clock buffer datasheet attached, XTAL TXC 8Y38472012 and low noise NCP163 LDO 2.5V used.

2015TXC_8Y_15.pdf (966.2 KB)
NCP163-D.pdf (1.3 MB)
PL135-47.pdf (356.8 KB)

Thank you!

Hi Lou.mobrey,

Since you are using a clock buffer, it is a similar approach to using external TCXO. Therefore, everything looks good except the DC block capacitance. You should use XTI pin for external reference overdrive pin. And XTO pin should remain floating. Thus, you should use 2200pF in series with XTI pin. In this way, there won’t be any DC offset on XTI pin.

Moreover, I would suggest that using a Phase noise analyzer to measure the quality of your clock signal and compare the phase noise values with the datasheet.

Best regards,
Emre Ozbas

Hi Emre,

Thank you for your comments.
I did exactly the same as you noted.
In my rework I have 2200pF connected in series with XTI pin (H15) and external clock buffer connected to this 2200pF capacitor. The XTO pin (G14) left floating.

Subject of rework:

  • XTAL removed;
  • XTAL capacitors removed;
  • trace going from G14 to XTAL cap. pad was cut off;
  • XTAL capactor’s pads used to solder 2200pF capacitor across;

I do not have concern about circuits, but signal level at XTI (H15) after 2200pF cap. concerning me.
When no external clock, but DW3000 powered, I see positive DC offset +500mV at XTI pin.
When clock is presented - the clock shifted negative around -500mV at XTI pin.
I’m not sure it’s correct or not.
I have measured clock signal at XTO floating pin and found it +/-1V symmetrical related zero level.

Just wouldlike to make sure nothing is wrong with those levels.

Tnank you!

Hi Lou,

It is expected because DC offset at XTI pin present there and coming from IC although there are DC block capacitor. Thus, it should be working. But I am not sure of the performance of your setup because we don’t know phase noise of reference clock.


Thank you for review and comments. We are testing performance.