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LMX2571: How to implement FM modulator

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Replies: 3

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Part Number: LMX2571

Hi Team,


Please advise me on my questions bellow.

I wan to implement FM modulator using say LMH2571.

According to E2E article, there are two ways, analog and digital method.


Q1. Are there any TI designs which proof either or both ways?


Q2. In analog implementation, you can realize FM modulation tweaking VCO control voltage.

     Can you show me an example schematic which can tweak VCO control voltage?


    I concern that injecting audio signal to the loop filter may case substantial charge pomp

    current leakage casing the PLL out of lock.


Q3. The method, tweaking VCO control voltage, require low loop band width.

       If you need to support as low as say 100 Hz, PLL loop band width should to be

       lower than 100Hz.

       Can LMX2571 maintain good phase noise, or implement such low loop band width?