AD5930 strange behavior

Hi all,

I'm currently using the AD5930 as a function generator on a development board. The AD5930 is clocked with a 41.94304MHz clock signal resultig in a frequency increment of 2.5Hz.

The AD5930 allows fixed frequency mode as described in AN-1044. Furthermore the AD5930 supports burst mode by setting the burst time register (TBURST). I now wanted to combine both modes in a fixed frequency burst.

Therefor the AD5930 is configured as described in the datasheet and the application note to a fixed number of output waveform cycles. This works well up to the point the number of "on" cycles plus "off" cycles exceed the value of 48.

For example a 1MHz burst signal with 24 cycles (24µs) and further 24 cycles off time (further 24µs) works well, but the combination 25 cycles burst (25µs) and 24 cycles off time (further 24µs) doesn't work.

I've also tried to manually set the register values to exclude a bug in my software, the result is the same.

Up to now I couldn't find a correlation to explain this behavior.

Can anyone confirm that the AD5930 behaves this way? Is there a possible work around know?

Thanks for your reply.

Kind regards, HSGIMAT

  • Me again,

    to give it some more detail:

    Syncout is used as trigger source for scoping. With Syncout configured to show the end of a sweep I get a burst with 24 periodes on and 24 periods off time and a 96µs trigger interval. That's what I would expect.

    With 25 periods on time and 24 periods off time the result is a continuous wave with a 98µs trigger interval at the above given example of 1MHz output frequency and the AD5930 clocked with the 41.94304MHz.

    Kind regards, HSGIMAT

  • 0
    •  Analog Employees 
    on Oct 4, 2011 6:17 PM over 9 years ago

    Moved this discussion from the RF Components community to the DDS Community.

    Eamon

  • 0
    •  Analog Employees 
    on Oct 4, 2011 7:12 PM over 9 years ago

    Hi HSGIMAT,

    Can you give some scope plot examples here if possible? I don't think I have seen this issue before.

    Regards,

    Liam

  • Hi Liam,

    sure I can show some pictures. I could isolate the problem a bit more detailed. Fmclk is still 41.94304MHz, the AD5930 is configured for burst and single frequency output (1MHz), as you can see in the proramming sequences.

    In the first case the AD5930 is configured with burst to a multiples of MCLK periodes. Programmed sequence is:

    creg: 0x0E1F

    fstart: 0xCA80 0xD061

    deltaf: 0x2000 0x3000

    ninc: 0x1002

    tint: 0x67DD

    tburst: 0xA3EE

    That means 24µs on and 24µs off time or elsewise expressed 24 periods on and further 24 periods off, remember the output frequency of 1MHz. This is what the picture 1 shows. Everything is fine up to here.

    In the second case the AD5930 is configured with burst to a multiples of MCLK periodes. Programmed sequence is:

    creg: 0x0E1F

    fstart: 0xCA80 0xD061

    deltaf: 0x2000 0x3000

    ninc: 0x1002

    tint: 0x699B

    tburst: 0xA418

    That means 25µs on and 24µs off time or elsewise expressed 25 periods on and further 24 periods off. The result shows picture 2, it's a continuous wave output, a strange behavior.

    In the third case the AD5930 is configured with burst to a multiple of cycles of the output frequency, 25 periods on and 24 periods off time. This works fine. Programmed sequence is:

    creg: 0x0E1F

    fstart: 0xCA80 0xD061

    deltaf: 0x2000 0x3000

    ninc: 0x1002

    tint: 0x4031

    tburst: 0x8019

    Any ideas?

    Kind regards, HSGIMAT

  • Hi Liam,

    I wonder that noone has answered yet. Could you or your team members verify the problem with the behavior of the AD5930?

    Kind regards, HSGIMAT