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LMX2572: Design Freq Hopping System with LMX2572

Derek Wang
Intellectual 615 points
Part Number: LMX2572

Hi TI Experts, 

I would like to use LMX2572 to design frequency hopping system with 1000 hops in one second.

I know I can trigger Muxout pin to monitor VCO Cal Time, and the window of VCO Cal signal is total VCO calibration time.

If I set frequency A hop to frequency B, 

How do I know the exactly time that the signal is disappear on frequency A and appear on frequency B ?

Thanks a lot.

Derek

  • 0
    TI__Mastermind 18070 points

    Hi Derek,

    Our expert on this series of products, Dean, is on vacation until Sep 4. Dean didn't leave much documentation on 2572, so please refer to the following notes on 2594 and see if it helps:7651.Fast frequency switching full assist.pdf

    Regards,

    Hao

  • 0 in reply to Hao Z
    TI__Guru* 98160 points
    Hi Derek,

    Here is some basic on the synthesizer lock time.
    The total lock time when you switching from one frequency to another is equal to:
    1. Register programming time. It depends on how many register you need to program and how fast you are programming it. You can also use Double Buffering to buy some programming time.
    2. VCO calibration time. It is an open loop operation. The calibration time depends on the VCO core and the reference clock (OSCin) frequency. For example, if the new frequency is at VCO6, then the calibration time will be the longest. It is because the calibration algorithm will select the right VCO core in an ascending order. (You can change the algorithm or tell the device where to start calibration with, see datasheet for details). Also if you want a shorten calibration time, use higher foscin. It is because the calibration runs on foscin.
    3. Analog lock time. After calibration is done, the device will close the loop. There is some close loop lock time, which is dependent on the loop bandwidth. Theoretically speaking, the lock time is approx. equal to 4/loop BW. For example, if the loop bandwidth is 100kHz, then the lock time is 40µs.
    You can use OUT_MUTE to mute the output during VCO calibration.
  • 0 in reply to Noel Fung
    Intellectual 615 points
    Hi Noel,

    Thanks for your replys.

    I am going to use this chip in frequency hopping system with 1000 hops / sec.
    Example :
    Frequency A = 2GHz
    Frequency B = 3GHz
    I need to know what exactly time the signal is disappear on frequency A after I click button in TICS GUI.
    and what exactly time the signal appear on frequency B.

    The instruments I have are Spectrum Analyzer and High Speed Oscilloscope.
    Do you know how do I measure it ?

    p.s. Before asked, I have use Spectrum Analyzer with zero span mode to get signal hopping from 2GHz into 3GHz at 3GHz frequency setting.
    But I cannot catch signal at 2GHz frequency setting to see the signal disappear, and know LMX2572 take how much time to let signal disappear at 2GHz.

    Sorry, If I have anything do not explain clear enough, please feel free to let me know.
    Thanks for your great helps.

    Derek
  • 0 in reply to Derek Wang
    TI__Guru* 98160 points
    Hi Derek,

    The output will not disappear unless you mute the output during frequency switching.
    The switching time is not a fixed value, I have explained the factors that determine the switching time.
    To measure switching time, you'd better had a modulation domain analyzer or a test equipment that can measure the transient response.