Post Go back to editing

ADF4159 PI and T attenuator

Category: Hardware
Product Number: ADF4159

Hello team,

We have designed a PLL card taking ADF4159 EVM as reference. Our requirement was to generate a frequency between 9.3GHz and 9.45GHz, so accordingly we have designed the loop filter in the card and the VCO we used was HMC510LP5E. Reference input frequency was 100MHz.

One thing that differs our designed card and EVM design was the inclusion of T attenuator along with the PI attenuator.  We included only the PI attenuator. Due to which we assume that RF IN (VCO/2 of the HMC510LP5E) that was fed to PLL chip has exceeded the RF input power range i.e., -10 to 0dBm.

Our queries are

1. Can the exclusion of T attenuator affect the phase noise of the RF signal?

2. We are able to see spurs at -50dBc/Hz to peak signal. Can the spurs be generated due to non-presence of T attenuator in our design?

3. Can it lead to thermal shutdown of the PLL? We observed the thermal shutdown of PLL when the pll was kept in thermal chamber where temperatures were greater than the 55 degree centigrade.

Your answers will be helpful.

Thanks,

GAR.

Top Replies

    •  Analog Employees 
    •  Super User 
    Aug 29, 2023 +1 verified

    Hi  ,

    In the evaluation board, we have two attenuation structures, One is Pi-Attenuatetor which is placed to provide 3dB attenuation for the RFIN pin of the ADF4159. 

    Another one is the T…

Parents
  • Hi  ,

    In the evaluation board, we have two attenuation structures, One is Pi-Attenuatetor which is placed to provide 3dB attenuation for the RFIN pin of the ADF4159. 

    Another one is the T structure which is placed on the evaluation board to serve as a resistive power divider. This structure also provides attenuation around 6dB.

    Therefore, there is a total of 9dB attenuation in this path

    In your system, there is only 3dB attenuation. The output power of the HMC510 is 4.7dBm, this will exceed the maximum ratings of ADF4159. Anormal behaviors most probably result from this violation. 

    I recommend changing the Pi Attenuator value to 6dB in order to stay within the limits of recommended specifications. 

    After this modification, if the issue persists we can continue to debug your project.

    Thanks,

    Emrecan

Reply
  • Hi  ,

    In the evaluation board, we have two attenuation structures, One is Pi-Attenuatetor which is placed to provide 3dB attenuation for the RFIN pin of the ADF4159. 

    Another one is the T structure which is placed on the evaluation board to serve as a resistive power divider. This structure also provides attenuation around 6dB.

    Therefore, there is a total of 9dB attenuation in this path

    In your system, there is only 3dB attenuation. The output power of the HMC510 is 4.7dBm, this will exceed the maximum ratings of ADF4159. Anormal behaviors most probably result from this violation. 

    I recommend changing the Pi Attenuator value to 6dB in order to stay within the limits of recommended specifications. 

    After this modification, if the issue persists we can continue to debug your project.

    Thanks,

    Emrecan

Children
No Data