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LMX2595: frequency above 19GHz

Flavio Heer
Prodigy 60 points
Part Number: LMX2595

What limits the frequency of the LMX2595 at 19 GHz. There is a VCO capable of doing 15 GHz followed by a frequency doubler.

Does the 19 GHz correspond to the frequency range of the doubler?

Is it technically possible to generate slightly higher frequencies, for example 19.5 GHz or 20 GHz? 

  • 0
    TI__Mastermind 28011 points

    Flavio,

    Around 19.5 GHz, which is 9.75 GHz to the VCO, this switches from VCO core 2 to VCO core 3.  When this happens, the output power drops about 10 dB, but 1/2 harmonic does not.

    So you can get a 20 GHz signal out of this device, but you will find that the 1/2 harmonic at 10 GHz will be higher than the desired signal at 20 GHz.

    Regards

    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 60 points

    Thanks Dean,

    that makes a lot of sense and this is not a scenario we would want to work with.

    When does the switch happen, exactly at 19 GHz? Every 0.1GHz we would get in addition would help significantly. 

    Flavio

  • 0 in reply to Flavio Heer
    TI__Mastermind 28011 points

    Flavio,

    The switch happens exactly when the device uses VCO3 instead of VCO1 or VCO2, and this happens around 19.5 GHz, but is part specific.

    By setting VCO_SEL to "VCO2", then you can go maybe go a little higher, but not 20 GHz.  If you set VCO_SEL="VCO3", or a higher VCO, then this happens at a lower frequency.

    The 19 GHz spec may have 500 MHz margin, but as this is a guaranteed limit, it should have some margin.

    What I can tell you is that I have never seen a device that can hit 20 GHz with VCO2.

    I you want to push a few hundred MHz above 19 GHz, do so with the understanding that we do not guarantee this performance above 19 GHz.  With this understanding, if you want to go above 19 GHz, then be sure to set VCO_SEL="VCO2" and a typical device I have seen can get to 19.5 GHz, but as you are doing this at your own risk, I would put some margin.

    Regards,
    Dean


    Regards,

    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 60 points

    Hi Dean, 

    thank you for the response. We may test this and see if we can get 200 MHz. But, as you said, there is some risk involved. 

    Flavio