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Sampling with the ADC12J4000 at rate lower than 1.96608GSPS

Boaz Rippin
Prodigy 70 points
Other Parts Discussed in Thread: LMX2581, ADC12J4000, ADC12J4000EVM

I am using the ADC12J4000EVM together with the TSW14J56EVM. The SW I use is High Speed Data converter Pro 2.6, together with the ADC12J400EVM GUI version 1.3

Running with an internal clock -- the lowest frequency I can set up the ADC12J400EVM using GUI version 1.3 is 1966.8MSPS. If i want to set it up to a  lower sampling frequency, how should I do it? Can this be done via the specific configuration of the chip registers?

Thanks

Boaz 

  • 0
    TI__Mastermind 44680 points

    Hi Boaz

    The most flexible way to sample at other rates is to re-configure the board for external clocking and use a bench RF clock generator. The modifications are described in the EVM User's Guide in section C.2. When using an external source it is best to use a bandpass or lowpass filter on the generator output to remove harmonics and noise.

    There isn't any easy way to arbitrarily set a non-standard frequency. If you have a specific sample rate in mind I can create a custom register setting file for the LMX2581 and post it on the forum.

    Regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Prodigy 70 points

    Thank you Jim

    Since the lowest available sampling rate is 1966 MSPS, it would be helpful if you could publish settings for 550 MSPS and 1200 MSPS, that, together with the available rates shall cover a wide range of rates.

    Best regards

    Boaz 

  • 0 in reply to Boaz Rippin
    TI__Mastermind 44680 points

    Hi Boaz

    The 550MSPS request is below the lower clock frequency limit (1000 MHz) for the ADC12J4000.

    I will create a setting file for the LMX2581 that generates a clock at 1200MHz.

    Regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Prodigy 100 points
    Hi,

    I am also using the ADC12J4000EVM together with the TSW14J56EVM.
    I tried to configure the LMX2581 via the Low Level View to get another sampling rate than the by the ADC12J4000EVM Gui (v1.3) provided. It did not work, even if I read only one Register from the LMX2581 the PLL get´s unlocked.
    So I tried to add a new configuration file to the GUI (I added a file to the Configuration Files Folder) but I didn´t find a way to load the file to the LMX2581 in the GUI.
    Which way do you recommend to configure the LMX2581 for another sampling rate and do I have to reconfigure the LMX2581 too?

    Best regards,
    Markus
  • 0 in reply to haertlms
    TI__Mastermind 44680 points

    Hi Markus

    Unfortunately it's not really possible to interactively change the LMX2581 frequency through the Low Level controls for that device.

    I'm writing up a procedure that should work to support other LMX2581 frequencies using configuration files in the same format as the ones included by default. If you have a specific frequency you need right now please let me know, and I'll provide a .cfg file for that frequency with the procedure.

    Regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Prodigy 100 points

    Hi Jim,

    Thank you for your response.

    A procedure so that I could configure other frequencies would be very helpful. I have a specific frequency (2460 MHz) but I don´t need it now and probably I can also use the provided 2457,6 MHz in this case. But it is possible that the the needed sampling frequency changes and therefor it would be good if I could configure the LMX2581 by flexible by myself.


    Regards,

    Markus

  • 0 in reply to Jim Brinkhurst1
    Prodigy 70 points

    Dear Jim B.

    Following your answer from July and Markus' request -- could you publish or send me  the CFG file for 1200MHz frequency

    Many thanks

    Boaz

  • 0 in reply to haertlms
    TI__Mastermind 44680 points

    Hi Markus

    Attached is a configuration file to set the LMX2581 to 2460 MHz. Please give it a try, by copying it to this file location: C:\Program Files (x86)\Texas Instruments\ADC12J4000EVM GUI\Configuration Files  (assuming the software is installed in the default location)

    LMX2581_Fs_2460Msps.cfg

    To use this I would first configure the EVM GUI settings to External clock mode, with a frequency of 2460 MHz and then click the Program Clocks and ADC button. Then navigate to the Low Level View tab and Open the new file "LMX2581_Fs_2460Msps.cfg".

    After this file is loaded, then navigate to the JESD204B/DDC tab and click on the JESD Block Enable button two times to stop and re-start the link. Then navigate to the Control tab and click on the Execute Foreground Calibration button one time to re-calibrate the ADC at the new operating frequency.

    At this point you should be able to configure the HSDC Pro capture software and capture data at this sample rate.

    I'll publish the procedure to create the custom LMX2581 configuration files in a separate post.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    TI__Mastermind 44680 points

    Hi Boaz

    Here is a configuration file to set the LMX2581 to 1200 MHz output rate.

    LMX2581_Fs_1200Msps.cfg

    Please follow the procedure described in my previous post to pre-configure the board, load the file and initialize things appropriately.

    Best regards,

    Jim B