ADL5569 power gain


I am using the ADL5569 op amp to an ADC and am currently doing a line up analysis of the system.  I want to use the single -ended input configuration determine the power gain of the system.  The datasheet lists the voltage gain only.  Using the s-parameter data, I was hoping to calculate a small signal gain approximation of the power gain (with the input matching network from 50 ohm) to place into my line-up analysis.  How would I go about this?  I am using an ideal transformer at the output which transforms the signal to a 50 ohm single ended output to estimate the gain, but the result does not make sense. 

Am I interpreting this correctly?  How exactly is the voltage gain measured, as in how is R_L loaded and where is Vout being measured?

  • +1
    •  Analog Employees 
    on Mar 11, 2020 1:38 PM

    This is tricky because ADL5569 is designed to be operated mis-matched, that is, it has an output resistance of 14 ohms but is specified driving 100 ohms. And the voltage gain is specified under those conditions. If you are going to make a model that shows the power gain, the model needs to have an input resistance of 100 ohms and an output resistance of 14 ohms. You figure out what the power gain would be if the device was matched on the input and output (i.e. Rload = 14 ohms; this is just a theoretical number; you cannot load the output with 14 ohms). Then in your simulation, you put a 100 ohm load on the part. You should then get the voltage gain number from the datasheet.

    An attempt is made to do this in ADIsimRF which has a model for ADL5569. You may find this helpful. This is diff-in diff-out though. I'm not sure what to do about the single-ended input drive.

  • What is the condition the s-parameters are measured?  Is it a 50 ohm system directly into the chip, or is there additional matching to 50 ohm when the measurement is formed?

    Thank you!

  • +1
    •  Analog Employees 
    on Mar 13, 2020 7:00 PM in reply to HJ_spex

    The s-parameters were measured with a 4-port network analyzer with a differential  impedance of 100ohms.  A fixture removal function was to move the reference plane to the DUT by was entering the length of the pcb traces.