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How to phaselock 33522B and 33622A using external TTL pulse as trigger

Question asked by arba87 on Oct 12, 2015
Latest reply on Nov 25, 2015 by cldiller
Hi all, 

I am trying to phase-lock three output channels from two Keysight function generators (33522B, 33622A). The 33522B serves as the master (1 output used) and the 33622A is the slave (two outputs are used).

So far I have used the approach presented in this video: In this approach, one device serves as master, the second device is the slave. Both devices are connected to the same 10MHz reference signal. In addition, master and slave are linked to each other via a BNC cable that connects their EXT TRIG inputs. All outputs are run in "burst mode" with an infinite amount of cycles. The slave's output channels are waiting for an external trigger (--> trigger mode is set to "EXT") and the master's output channel waits for a manual trigger. The manual trigger can either be given by pressing the "Trigger" button at the front panel of the master (33522B) or by sending a software trigger via a computer. In both cases, the master sends a trigger TTL pulse to the slave. This way of triggering gives three output signals that are phase-locked to each other.

My question is now the following.
I would like to use an external TTL pulse to trigger the output of both function generators. To do so, I set all output channels to trigger mode "EXT" (i.e. all output channels are waiting for a TTL trigger pulse) and connected the EXT TRIG inputs of the two function generators to my external trigger pulse. If I now send the trigger pulse, the two function generators will start delivering a signal. So far so good. However, I discovered that the three output signals can have varying relative phases, even though I specified the phase offset of each signal to be of zero degrees. Moreover, the relative phases of the three signals will also change when I trigger the output another time. 

In conclusion, I am looking for a method to phase-lock two function generators by using an external TTL pulse. Right now, I can trigger the two generators such that they start the output of the desired signal at the same time. The relative phases of the created signals are however 1) not reproducible and 2) do not correspond to the values I asked for when configuring "burst mode".

Can anyone help me out?