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3406B AWG output sampling

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3406B AWG output sampling

Postby naminator2003 » Tue May 26, 2015 4:36 pm


I am using the AWG from Picoscope 3406B for generating different waveforms, generally containing linear slopes and fixed values (something like a trapezoid shape signal). I am using standard Picoscope 6 software, updated to the latest version. I can see that the output signal's number of samples can be configured to any value between 128 and 16382. The signal is read from a .csv file.
Is the AWG coherent from one generated period to another, no matter what the number of samples is ? My applications is highly dependent on this phase coherence.
I have noticed that I can select almost any output frequency for the AWG, which means that the wave can be stretched or shrink-ed on the time axis with any factor. Is there any relation between the wave number of samples and the output frequency, so that the generator is coherent ?
In other words, what is the output sampling frequency of the DAC inside? is it always 20MS/s, as stated in the datasheet, or can it be less?

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Re: 3406B AWG output sampling

Postby Hitesh » Fri Jun 05, 2015 10:25 am

Hi Mihai,

The DAC frequency is always 20MS/s. There is a description in the Programmer's Guide (see section 4.54 in the document available via https://www.picotech.com/download/manuals/PicoScope3000SeriesAApiProgrammersGuide.pdf):

The arbitrary waveform generator uses direct digital synthesis (DDS). It maintains a
32-bit phase accumulator that indicates the present location in the waveform. The top
bits of the phase accumulator are used as an index into a buffer containing the
arbitrary waveform. The remaining bits act as the fractional part of the index, enabling
high-resolution control of output frequency and allowing the generation of lower

There is a better level of control when using the Software Development Kit in order to control the AWG. The PicoScope 6 software interpolates the data from a csv file to a large number of samples and also the rate of stepping through the buffer is calculated from the requested frequency and number of samples, so it makes it difficult to know the settings to use in order to get the exactly the same samples out on each cycle through the waveform.

I hope this helps.


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