WRS-FL-LJ
This report shows the performance of WRS-FL-LJ, a special version of
WRS-FL[1] with low-jitter circuits support.
Comparing to standard WRS-FL, the WRS-FL-LJ includes two major
improvements:
1: adding a extra AD9516 for 10MHz clock input
2: replacing the TCVCXO VM53S with a better TCVCXO or OCXO (
T604-025.0M[2] used in this test).
The phase noise performance and Allen deviation test results are summarized below.
| WRS-FL-LJ as GrandMaster | WRS-FL-LJ after 10 cascade stages | |
|---|---|---|
| Phase Noise Performance | -100.1dBc/Hz at 1Hz, -103.0dBc/Hz at 10Hz, -119.8dBc/Hz at 100Hz, -135.5dBc/Hz at 1KHz | -87.1dBc/Hz at 1Hz, -84.3dBc/Hz at 10Hz, -115.7dBc/Hz at 100Hz, -134.9dBc/Hz at 1KHz, |
| Allen Deviation | 7.97E-11 (Tau=0.01s),1.23E-11 (Tau=0.1s),1.32E-12 (Tau=1s),1.43E-13 (Tau=10s) | 1.93E-10 (Tau=0.01s),9.57E-11 (Tau=0.1s),9.98E-12 (Tau=1s),9.24E-13 (Tau=10s) |
| PPS/10MHz Jitter | < 10ps | <10ps |
1. Measurement setup
- 10 WRS-FL with low jitter circuits, one acts as GM and the others act as Boundary(Slave)
- Several 3 meters fibers
- Several 1 meter coaxial-cables
- Symmetricom 8040C - Frequency Standards
- Microsemi 3120A as phase noise analyzer. Currently, the device cannot get the modified allan deviation and time deviation as lacking of copyright
- High performace oscilloscope, Lecroy HDO9108A, 12bit, 10Gbps, 1G input bandwidth
- Warm-up time: Slave 1-9 reach full thermal stability after 24h of continuous running. Grandmaster, 8040C, 3120A, HDO9108A run for about 2h before starting the measurements below.
- Teshbench is as shown in Figure 1. The connections of performance test are illustrated on Figure 2 and Figure 3. Rubidium clock source (Microsemi 8040C) is chosen as the time reference. Ten layers of WRS-FL-LJ are cascaded in the performance test. Port 1 and port 2 of each WRS-FL-LJ act as slave and master respectively. Phase noise performance is measured by 3120A while the skew jitters of PPS/10MHz out are measured by the oscilloscope. Phase noise tests are done one by one while the skew jitter tests are run in parallel. As the limited ports of oscilloscope, only GM, Layer-1, Layer-2, Layer-3, Layer-4, Layer-5, Layer-7, Layer-9 WRS-FL-LJ are tested.
The gateware running on all switches is based on wr-switch-sw v5.0.1 and mattia low jitter branch. All source code could be found at branch hm-wrsfl-lowjiiter, wr-switch-sw[3]/wr-switch-hdl[4]/wrpc-sw[5] repository.
2. Experimental results
2.1 Phase noise measured by 3120A
Figure 4 and Figure 5 show the phase noise performance of different
layers of WRS-FL-LJ, in which the blue trace is the GrandMaster
WRS-FL-LJ.
2.2 Allan deviation measured by 3120A
Figure 6 and Figure 7 are the results of allan deviation of different
layers of WRS-FL-LJ, in which the blue trace is the GrandMaster
WRS-FL-LJ
switch.
2.3 10MHz clock out jitter performance measured by oscilloscope
Figure 8 shows the 10MHz clock out jitter between the Grandmaster and WRS-FL-LJ in different layers, in which CH1 is the 10MHz clock out of Grandmaster. The skew means the time difference at 1-volt between two input 10MHz clock.
2.4 PPS out jitter performance
Figure 9 shows the PPS out jitter between the Grandmaster and WRS-FL-LJ in different layers, in which CH1 is the PPS out of Grandmaster. The skew means the time difference at 1-volt between two input PPS signals. The test lasts about 2.7h.
3. Summary
This report talks about the preliminary performance test of WRS-FL-LJ.
The phase noise performace, as well as the allan deviation performance
are worsen along with cascaded levels increase. However, the phase noise
performance of ten stage cascade still remains relatively low. These
results show huge improvement comparing to normal WR Switch and that's
the reason why the PPS out /10MHz out skew jitter is below 10ps after
ten stage cascade connection, which has a large improvement comparing to
current WR Switch (~90ps skew jitter after 10 stage cascade
connection).
In future, more performance test could be done with other measurement
devices. More compatible TCVCXO and OCXO will also be tested to achive
better performance.
[1] https://www.ohwr.org/project/wrs-fl-hw/wiki
[2] http://www.conwin.com/datasheets/tx/tx176.pdf
[3] https://www.ohwr.org/project/wr-switch-sw/tree/master
[4] https://www.ohwr.org/project/wr-switch-hdl/tree/master
[5] https://www.ohwr.org/project/wrpc-sw/tree/master