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White paper on HS DAC built in interpolation, and new mix modes to get signals in higher nyquist modes?

Viktorija Cecil
Mastermind 18501 points


Team, 

My customer is asking:

We are looking into RFDACS. I’m aware of built in interpolation, and new mix modes to get signals in higher nyquist modes.

Is there a design or planning document to work out the process?

 

E.G. we have a 45 and 75MHz bandwidth signals. We want to use a single RFDAC to output in 700-900, 1700-1900, 2100, and 2600MHz bands.

This would dramatically simplify the up-conversion and with the exception of post filters, we might be able to use the same hardware.

Any reference, or guidance would be greatly appreciated.

Thanks

Viktorija

  • 0
    TI__Guru* 91947 points

    Viktorija,

    Is the customer trying to get both bandwidth signals up converted at the same time on a single DAC or two DAC's? In either case, this can be done with a single part. Do they want the signals up converted to all four frequency bands at the same time? What DAC sampling frequency do they plan on using? Attached are a couple of documents that may help them. 

    Regards,

    Jim

    RFSamplingTrainingBinder_v1p0.pdfIntro to RF Sampling.pptx3730.Multi-tone Gen TI Design.pdf

  • 0 in reply to jim s
    Prodigy 30 points

    Thanks Jim. As an old timer, these new dacs with interpolation, mix-mode nyquist, and NCO's, I'm not sure how to architect a configuration.

    Is there a tool to find the optimal nyquist zone, interpolation rate and NCO frequency? We are aiming to replace multiple upconverter designs with a single RF DAC design.

    No we do not need to transmit to all the bands simultaneously, but would like to be able to configure to do any band on the fly. Thank you for the documents. I will review them..

  • 0 in reply to John Washell
    TI__Genius 12965 points
    John,
    Also consider looking at this high speed DAC appnote.
    www.ti.com/.../slaa523a.pdf

    It talks some about interpolation and digital mixing.

    At a high level, I would consider interpolation as a means to allow you to input a low data rate signal (to simplify digital baseband processing) and then use the interpolation to expand the accessible nyquist band (you can extend this into high IF - 100s MHz, to RF up to 3-4GHz). The DAC NCO (32-48b accuracy, sub Hz) can then be used to shift this to any frequency within the output Nyquist (which will be Nx wider than the input signal datarate).

    So as an example, if you had a 75M BW signal, it would need an input datarate of about 100Msps complex (with 0 IF signal), or at least 150Msps real (IF signal at around 75/2M). You could then use interpolation to increase the output rate of the DAC to some number multiple of the input rate (lets say 64x) such as 100M input rate*64=6.4Gsps output rate. You could then employ a digital NCO mixer at 2GHz (well within your 3.2GHz Nyquist) to shift your signal there.

    At the analog output of the DAC, you will have your signal at 2GHz, as well as sinx attenuated images at each of the nyquist zones - these images can be filtered out with a wide simple analog filter.

    Ken.