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LMX2820: Implementation of PSYNC function

JH Shin
Guru 10890 points
Part Number: LMX2820

Hello,

My customer considers using the PSYNC function of the LMX2820 for multi-device synchronization.

1. Do they have to go through both 7.3.12.2.1 using MASH_SEED to Create a Phase Shift and 7.3.12.2.3 Fine Adjustments to Phase Adjust in the datasheet to use the PSYNC feature?

    Please explain the role of both procedures.

2. If there is any material that easily explains the procedure for performing multi-device synchronization using PSYNC, please provide it.

3. After performing PSYNC, how much can the synchronization difference between multi-devices be managed within?

Thank you.

JH

  • 0
    TI__Genius 10985 points

    Hello JH,

    JH Shin said:

    1. Do they have to go through both 7.3.12.2.1 using MASH_SEED to Create a Phase Shift and 7.3.12.2.3 Fine Adjustments to Phase Adjust in the datasheet to use the PSYNC feature?

        Please explain the role of both procedures.

    To set up PSYNC, you would need to go through section 7.3.12.2.1 to create a phase shift. The role of this procedure is explaining how to use MASH_SEED which is what sets the PSYNC functionality. It also covers a few considerations when setting up MASH_SEED. Section 7.3.12.2.3 just asks you to consider whether you are using static or dynamic phase adjust, and whichever you are using, how to set the LMX2820 for programming.

    Consider that the MASH_SEED word is constantly changing, by adding the previous value of MASH_SEED to a current value. If using static phase adjust, then you would require to set the MASH_SEED word to the desired value and toggling MASH_RST_N to force the value. However, if using dynamic phase adjust, you would set a smaller MASH_SEED value and the program would run through the summation described previously to add to a cumulative MASH_SEED value.

    JH Shin said:
    2. If there is any material that easily explains the procedure for performing multi-device synchronization using PSYNC, please provide it.

    I could not find any more material on setting PSYNC except section 7.3.12 that you've already reference and potentially this E2E.

    JH Shin said:
    3. After performing PSYNC, how much can the synchronization difference between multi-devices be managed within?

    We will get back to you on this later! Hope this helps.

    Best,

    Andrea

  • 0 in reply to Andrea Vallenilla
    TI__Guru** 106960 points

    Hi JH,

    Phase sync and MASH_SEED are two difference function. 

    MASH_SEED is used to adjust the RF output phase w.r.t. the input reference clock. It does not require PSYNC to work.

    Phase sync is used to make the delay between RF output and the input deterministic. After synchronization, the delay is approx. 60ps. This is written in the datasheet.

    We are working on an appnote on how to phase sync multiple LMX2820, hopefully it can be released within this month. Please check back ti.com in two weeks. 

  • 0 in reply to Noel Fung
    Guru 10890 points

    Hi Noel,

    Thanks for your reply.

    The customer has further questions.

    1. They are ultimately looking to achieve synchronization of multiple LMX2820s using only the PSYNC pin input.
        Is there any other procedure other than inputting the same SYNC signal to multiple LMX2820s? Please let us know if there is.

    2. If they synchronize 22 or more LMX2820s with only the PSYNC pin input, is the maximum time difference about 60ps correct?

    3.If the output frequency changes or the device resets after performing a PSYNC sync, will they have to perform the PSYNC sync procedure again?

    Best Regards,

    JH

  • 0 in reply to JH Shin
    TI__Guru** 106960 points

    Hi JH,

    Q1 and Q3, the user's guide I mentioned has addressed these questions. The user's guide will be available in ti.com on Tuesday US time. 

    Q2. The 60ps delay between input and output is a typical value, we do not have data showing the part to part variation.