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ADF4360-8 Compensation Node

Category: Hardware
Product Number: ADF4360-8
Software Version: N/A

Using the ADF4360-8 in a FM modulation scenario generating a VHF carrier with an audio signal tied into the VTUNE pin.  Loop filter is configured with a cutoff frequency of 100Hz to allow the audio to pass through the PLL.

As the FM deviation is increased above 20kHz, the harmonics in the received demodulated audio increases which is a concern for our application.  Desired FM deviation is 75kHz but based on measurement need to keep FM deviation below 20kHz to manage harmonic levels.

Looking for more information on the Internal Compensation network as the harmonic content is present on the CC pin.  Currently using the suggested decoupling (CC = 10nF and CN = 10uF) but there is limited info on the what the internal compensation consists of and any possibility of optimization with these pins.

  • Hi,

    I do not have any experience with generating FM modulation by driving audio signal into Vtune pin. Based on the ramping PLLs (ex. ADF4159) datasheet, I would expect the LBW to be wider. Such 100Hz narrow BW may cause the PLL to unlock. Perhaps your application is different and that works for you.. 

    Regarding the CC and CN pins, not sure what I can provide other than the caps on these nodes are used as bypass caps and to filter out the noise. You may try different values to see if they help. You may also try connecting the cap on CN to GND instead of VVCO. 

    Regards, Kazim