Trigger output delay and jitter on Rigol scopes
After the recent postings about possible jitter problems on the 1000Z series, I couldn´t resist to run some tests of my own, especially since I´ve got access to the three (lower) lines of recent Rigol scopes which are DS1054Z, MSO2072A-S, MSO4014, all "improved" to the highest possible version and with the latest firmware installed. Actually, I´m now able to report some interesting findings and maybe a bug or two...
What did I test?
I fed a 100kHz square wave signal (on MSO2072A-S and MSO4014 from the internal generator of the MSO2072A-S and on the DS1054Z from a Hantek HDG2002B). I verified before that these sources are fairly free of phase jitter by phase comparison with a rubidium oscillator.
I connected the trigger out signal of the scopes to the second or third channel (of the same scope of course) in order to measure trigger out delay and phase jitter. In case of the DS1054Z, I also inserted a delay of 50ms to view the 5000th slope of the 100kHz signal after the trigger.
What did I find?
DS1054Z:
Trigger out delay: 355ns
Trigger out phase jitter: 8ns
5000th slope delay jitter: neglible, some 1/f type drift observable
MSO2072A-S:
Trigger out delay: 219ns
Trigger out phase Jitter: 8ns
MSO4014:
Trigger out delay: 30.5ns
Trigger out phase jitter: approx. 300ps
The trigger out delay is extended by the delay of the BNC cable, so in reality it may be a few nanoseconds less than specified.
What does that mean?
Apparently, the trigger out phase jitter of the two lower models isn´t related to PLL jitter since the 5000th slope is virtually jitter-free. The trigger out phase jitter must have its origin somewhere in the signal processing downstream of the triggering logic / slope discrimination itself. The relatively long delay between the trigger event itself and the signaling at the trigger output also indicates that something´s got to be going on there. Maybe the triggering is done in software. This may also explain the high phase jitter of 8ns on both the DS1000Z and the MSO2000A machines (the same is probably valid for all the models in the corresponding classes).
On the contrary, the MSO4000 series almost for sure has implemented the triggering logic completely in hardware (FPGA). The extremely short delay of the trigger out (about 30ns) and the virtually not present jitter is a clear indication for this.
What peculiarities did I find?
These basically concern the DS1000Z:
- If the scope is operated in "Zoom" mode (press the timebase sec/div button), and the acquisition is stopped (press RUN/STOP button), only the last trace is displayed on the screen, just as if the scope was operated in single shot mode. It´s doing this regardless of the selected display persitance time.
- In Zoom mode, if persitance time other than minimum or infinite is selected, the user interface gets so laggy it´s almost unusable.
- In Zoom mode and display persitance time other than minimum or infinite selected, the attempt to do a screenshot locks up the scope and requires a power cycle to get out of this (at least I didn´t find an alternative or didn´t wait long enough
).
Attached are some screenshots of the tests.
I hope this may be of interest for some of the readers.
Cheers,
Thomas