ADL5324 Datasheet

Hi,

In the ADL5324 datasheet there are reference designs and layouts.

On page 19, figure 17, the layout for the 3500-3700MHz operation. There is a series inductor on the output, L2.

It is 4.7nH.

At 3500MHz, this gives a reactance of 103 ohms.

Considering the output impedance is 50 ohms, this will attenuate the output signal somewhat....

Am I correct?

If so what value should this be?

Best regards,

Roger.

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  • Hi Rog,

                    the ADL5324 is not internally matched to 50 ohms. This impedance is 6 ohms or so and must be externally matched to 50 ohms. L2 & C2 work with the internal impedance of the ADL5324 to create a 50 ohm match for the ADL5324. The value for L2 is correct and has been tested.

    Regards,

    Jim B

  • Hi Jim,

    Ok, yes I see the S21 is 5.6 ohms and needs to be matched to 50.

    I am also trying to simulate this, but I cannot get it to match to 50.

    Do you have any spice or ADS simulation files on this device, I could then see how I am going wrong.

    Best regards,

    Roger.

  • Hi Rog,

    Is C2, the 0.75 pF cap placed? it is located 125 mils from the output pin. It works in conjunction with the inductor to match the output.

    Regards,

    Jim B

  • Hi Jim,

    Yes. Exactly to the datasheet.

    Does this act as a T network?

    Best regards,

    Roger.

  • HI Rog,

                     Yes, this would act like T network.

    Regards,

    Jim B

  • Hi Jim,

    I can get the S11 and S22 to dip at 3.5 and peak power at 3.5 but the shunt capacitor on the output is 2.0 pF - not 0.75... This is using ADS S parameters simulations.

    I am going to try out a range of cap values on my board and see what gives the best output.

    On a related not but slightly different, I am trying to model load pull.

    To do this I am using ADS harmonic balance.

    I therefore require a model for the ADL5324 that is similar to an actual RF transistor ie: not just it's S params.

    Do you have this?

    Best regards,

    Roger.

    PS: am getting there slowly...

  • Hi Rog,

                    Analog devices does not offer a transistor based models for RF amplifiers. There may be some error between ADS and built matching circuits. I have noticed this at some of the higher frequencies. So that may be why you have a different value inductor.  My trick when that happens, is to shift the frequency by the delta between the ADS freq and the freq the part is actually tuned to in real life. After 2nd simulation with the offset, I find the tuning is spot on.

    Regards,

    Jim B

Reply
  • Hi Rog,

                    Analog devices does not offer a transistor based models for RF amplifiers. There may be some error between ADS and built matching circuits. I have noticed this at some of the higher frequencies. So that may be why you have a different value inductor.  My trick when that happens, is to shift the frequency by the delta between the ADS freq and the freq the part is actually tuned to in real life. After 2nd simulation with the offset, I find the tuning is spot on.

    Regards,

    Jim B

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