Fixed phase relation between the two generators signal

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Bulova
Posts: 38
Joined: Fri Jan 09, 2015 6:07 pm
Location: Babenhausen/Germany

Fixed phase relation between the two generators signal

Post by Bulova » Fri Feb 20, 2015 2:57 pm

Hello,

is there any possibility to make a setup for the two generator outputs to create a fixed and defined phase relation? When I try the APP, I can create phase relations which seem to be shifted to any angle, but the result when I do so (by dejusting one of them to a slightly different frequency and then at a time back to the same frequency as the other generator output) seems to be random somehow and I doubt if this phase relation will be stable forever. To controle via console doesn't provide a phase declaration either, just channel amplitude frequency <type> only.

The goal for this application is to generate a tranducer signal and a rectangle signal for a synchronized rectifier respectively a lock-in amplifier. The phaseshift between thos two should be fixed and adjustable.

Is there a way theoretically in general?

Dieter

Nils Roos
Posts: 1441
Joined: Sat Jun 07, 2014 12:49 pm
Location: Königswinter

Re: Fixed phase relation between the two generators signal

Post by Nils Roos » Tue Feb 24, 2015 10:33 pm

Hi Dieter,

The internal architecture of the AWG guarantees that the phase relation between the two channels remains constant indefinitely, when both channels generate the same frequency.

The AWG also makes it quite easy to generate two signals with a defined phase relation. Program both channels with the same waveform, frequency etc., set the start offsets into the array of samples to appropriate values (ie reflecting the desired phase difference at the target frequency), start both channels simultaneously and you are done.

Unfortunately, neither the scope+gen app nor the generate utility offer a way to start both channels at the same time. You'll need to modify the software to do that. Or use the monitor command line utility to write to the AWG's control register directly, but that would be awkward.

Cheers
Nils

Bulova
Posts: 38
Joined: Fri Jan 09, 2015 6:07 pm
Location: Babenhausen/Germany

Re: Fixed phase relation between the two generators signal

Post by Bulova » Fri Feb 27, 2015 6:51 pm

Hello Nils,

thanks for the response. I thought already about such a way, although my command line knowlegde is not that experienced yet. But I will try to get through it.

In the meantime I found a different method: I used the possibility to load oscillation data into the buffer in the scope&generator-APP, where both oscillations represent the wanted phase shift to eachother. So far, so good. But in fact to avoid the random phase relation, I have to trigger the system externally. And if I want to have a free oscillating system, there is a need to trigger channel 2 by channel 1 i. e. Unfortunately the external trigger input (DIO_0P) prefers a CMOS level of about 3.3 Vpp, totally shifted into the positive range, while the generator's output just provides 2 Vpp symmetrical at maximum. With a combination of 2 resistors and one capacitor the trigger can work, but an active buffer would be more proper.

By the way I am just writing a small article for the magazine ELEKTRONIK PRAXIS, featuring RedPitaya as a possibility to manage complex measuring tasks. And the focus should be on its hardware capabilities.

Dieter

Bulova
Posts: 38
Joined: Fri Jan 09, 2015 6:07 pm
Location: Babenhausen/Germany

Re: Fixed phase relation between the two generators signal

Post by Bulova » Sat Feb 28, 2015 11:26 am

Hello Nils,

I found the script RedPitaya_HDL_memory_map, where all registers are described. I am missing a little bit some example syntax, especially for the ASG managing. For instance it is possible to identify

Code: Select all

monitor 0x40100004 0x8
that this could be the trigger source for the oscilloscope as 8-arbitrary wave generator application positive edge. But how to define scale and offset for the ASG after
Ch A amplitude scale and offset
?
monitor 0x40100004 0x4
and then? I have no glue. As I said some significant examples would be helpful to understand and to apply the right syntax.

Dieter

Bulova
Posts: 38
Joined: Fri Jan 09, 2015 6:07 pm
Location: Babenhausen/Germany

Re: Fixed phase relation between the two generators signal

Post by Bulova » Sat Feb 28, 2015 11:51 am

Hello Nils,

now I understand the meaning of the document -- I have to identify the right bit numbers and set them. The
monitor 0x40200004 0x3fff0000
would set the offset of channel A to a very extrem value. But still, there is no effect up to now on my RP. Maybe there are some other registers to setup first.

Some more tests ...

Dieter

Nils Roos
Posts: 1441
Joined: Sat Jun 07, 2014 12:49 pm
Location: Königswinter

Re: Fixed phase relation between the two generators signal

Post by Nils Roos » Sat Feb 28, 2015 11:57 am

Hi Dieter,

Since offset and amplitude share the same register, writing 0x3fff0000 would set the offset to 0x3fff and the amplitude to 0x0000, so I'd expect a flatline output at the max positive offset. The monitor utility always writes the full 32 bits.

Have fun experimenting,
Nils

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