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[FAQ] RF synthesizers: What is MASH order and how to determine the suitable MASH order in RF synthesizers?

Can you tell me what is MASH order and how to determine the suitable MASH order?

  • MASH order is equal to delta sigma modulator order.
    In general, use 3rd order for both integer and fractional channels. This way we don't have to worry about changing MASH order for every frequency channel we are working on.
    PLL N-divider has a minimum value restriction and this is MASH order dependent. Datasheet has the details of suggested N-divider vs MASH order. N-divider is the key factor that will affect our choice of MASH order.
    The order of MASH is proportional to the number of discrete N value that are used to implement fraction. In general, a higher order MASH returns better spurs but may degrade phase noise. This is because the PLL gets more randomization with higher order MASH.