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LMX2594PSEVM: LMX2594PSEVM frequency settling and sweep

Steven Nagle
Prodigy 10 points
Part Number: LMX2594PSEVM
Other Parts Discussed in Thread: LMX2820, LMX2594

Hi all,

Can anyone tell me if the LMX2594PSEVM board and/or the chips on this board, can sweep frequency, say, from 100s of MHz to 20 GHz in as little as 100 ns? I'm unfamiliar with the PLLs and VCOs, and my read of the datasheets suggests that individual frequency transitions require microseconds. If that is the case, what would be the proper chip to do fast high-frequency sweeps? Thank you for any info.

  • 0
    TI__Guru* 81400 points

    Hi Steven,

    A synthesizer cannot switch its frequency in nanosecond. 

    You may consider using two LMX2820 in ping-pong architecture to switch frequency. 

    Here is an appnote FYI.

    https://www.ti.com/lit/pdf/snaa357

  • 0 in reply to Noel Fung
    Prodigy 10 points

    Thank you for this.

    Could one use more than two synthesizers, synchronized, and do more than one step between a starting and ending frequency? It seemed that the LMX2594PSEVM could be sync'ed with additional LMX2594PSEVM boards, but I wonder if the mute and unmute transitions happen on the nanosecond timescale, and can be offset within a few nanoseconds reliably?

    The reason that we want a frequency sweep is to drive en electro-optic modulator (EOM) which itself is steering a beam to move a trapped atom.

  • 0 in reply to Steven Nagle
    TI__Guru* 81400 points

    Hi Steven,

    The phase relationship between two sync'ed LMX2594 will change after frequency is changed, we will need to sync them again. Each synchronization takes time (hundreds of µs).

    If you need linear frequency sweep between 100s of MHz to 20GHz, this is not possible with any synthesizer. 

    If staircase frequency sweep is acceptable, LMX2820 is the best option.

    Mute and unmute in LMX2594 requires register programming. In addition, output does not shunt down or enable sharply, it takes 2.5µs to gradually turn ON or OFF.