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DDS with phase marker?

Hello,

I am designing a Howland Current Pump, and I have previously used the AD9954 and AD9833 to generate the sine waves. I was looking to use the AD9102 as it seems easier to get hold of from suppliers, and has a broader frequency range for a single clock.

However, one feature I would like to add to my design is a phase marker i.e. a pulse on another pin when zero phase is reached. Is there a DDS IC that has this feature? or is there an example circuit (like a comparator after the DAC output?) 

Thanks for any advice you can offer!

Jimbles

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  • Hey Will,

    I wasnt sure if the comparator could be used at the same time as the sine wave generator? As I was looking at the AD9954 evaluation board, and it looks like you have to select which output you wish (Note 4 page 36 of datasheet). Have I got this confused? 

    Thanks

    Jimbles

  • Hello Jimbels,

    The datasheet assumes that you either want a sine wave or a square wave, which is the case for most users. But since you want both you can use both. Depends on how much you care about the alignment between the sine wave and the square wave, you might not want to use two separate filters, especially if the two filters have different transfer functions, which looks like the case in the datasheet. You can potentially just have one differential filter between the transformer and IOUT/IOUTB, and feed the comparator from the output of the filter is kick back is acceptable.

    Regard,

    Will

  • Hi Will,

    Thanks again for your input. I think an external comparator might be a good solution in my case. I was looking into the AD9102, and there is the DOUT pin which can be controlled by the pattern generator. Does this still work with continuous waveforms? As that might be a good enough for my needs.

    Regards,

    James

  • Hello James,

    The DOUT pin can be configured to indicate either the pattern generation is on or off. I am not sure if it works in DDS mode, but even if it does, it will just stay high while the DDS is running, rather than send out a rectified (or MSB) of the sine wave.

    Regards,

    Will

  • Ah I see! That makes sense. Thanks for your continued advice

    James