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Hello Sir/Madam,

I am using ADL5380 eval board for same RF/LO Frequency. I have Given both the Input signals through Splitter for synchronizing the input signals. With the guidance of this forum i have bypassed the output side baluns to pass DC value and at R7x and  R6x i have populated a resistor of 500 ohms.  Do you have any data of what should be the IP, IN, QP and QN data for same Input frequency?

According to the datasheet, the impedance of single ended output is 25 ohms and oscilloscope which i am using has an impedance of 50 ohms. So do i have to  use impedance matching circuit between Eval Board and oscilloscope?

Also when i bypass the balun, the circuit becomes differential so can i terminate the port IN and QN port with 50 ohm termination?

  • Hi Ankita,

    • I responded to the other forum thread with some additional guidance for akshay92; please review.
    • You should connect the 500 ohm differential load impedance in place of R7x and R6x. No additional terminations are needed.
    • Also, be careful connecting the baseband outputs into a 50 ohm oscilloscope, because DC voltage will be present. Depending upon oscilloscope, you could exceed the maximum input limit. It's best to observe the baseband outputs with high impedance probes or a DMM, since it's a DC voltage.
    • For the LO/RF signals there will be no issue using 50 ohm impedance test equipment or oscilloscope with 50 ohm input setting.

    Best Regards,


  • Thank you Sir for the quick response.

    I have a doubt regarding outputs. When i am connecting the Ip and Qp to the oscilloscope ports and when i am switching ON the 5V supply only, the output voltage obtained is Ip = 1.7V and Qp= 1.84v. Can you explain me what exactly is this output??

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  • Hi Ankita,

    You're welcome.

    What is the voltage on In and Qn?  You should look at the difference voltage across the 500 ohm load resistor between Ip and In; Qp and Qn.

    If possible, provide a markup of board schematic and a block diagram of your test setup, as this will help troubleshoot.

    Best Regards,


  • Hii Sir,

    Thank you for the response sir. 

    I have attached below the block diagram of my setup and the readings taken with various cable length for phase variation. 

    I have kept the In and Qn port open and just connected Ip and Qp to oscilloscope. When i turn ON only the power Supply(and not RF/LO)  the voltage across R6x and R7x resistor is 840 mV and 930 mV.

    And when i turn ON RF/LO, the voltage varies till approx. 1200mV for different cable length.

    The readings below of VIp and VQp are taken across  500 ohms resistor R6x and R7x  with the help of DMM. But how can i get the outputs at the SMA ports.


  • Hi Ankita,

    • The importance is the DC voltage across the load resistor. As the phase changes it causes the output stage to pump current from one side of the diff pair to the other.
    • Attached is an example diagram for your application. Please try that setup or something similar for measuring the DC voltages across the resistors.
    • As noted in the other thread, you will need to remove the resistor on the ADJ pin for operation above 5GHz.
    • Also, please see this article regarding system phase error calibration when using the ADL5380. Depending upon the implementation and configuration, you may need to follow this guide once you have DC voltage vs phase data.

    Best Regards,


  • Ok, Thank you sir. 

    I tried integrating INA114 instrumentational amplifier with the ADL5380. 

    The same results are obtained as before. when I turned ON the DC supply, the Qp, Ip output of ADL580 was 2.5 V and when i turned ON the RF/LO there was no change in the output of ADL5380 which was 2.53 which was same when i turned on only the DC Supply.

    Sir, what is this resistor for at pin 19?

  • Hi Ankita,

    • I'm not sure why the DC voltage would be present when you turn off the device. There must be something still powered in your setup or there is some capacitance which has been charged.
    • Before connecting the instrumentation amplifier, try getting the ADL5380 working by itself. You should be able to verify functionality with a DMM and then sweeping the phase difference between the RF and LO paths.

    • Regarding pin 19, the pin descriptions in the datasheet state: "A resistor to VS that optimizes third-order intercept. For operation 5 GHz, RADJ = open. See the Circuit Description section for more details."
    • Leaving the resistor open on that pin will optimize the non-itineraries in the mixer for operation above 5GHz.

    Best Regards,


  • Ok Thank you sir. By implementing the changes suggested by you, i' ll get back o you.

  • Hello Sir,

    By testing the ADL5380 board individually, When i am switching ON the  DC supply and RF/LO is OFF, the Voltage across load resistor is 1.4V at I and Q.

    and when i am switching ON the RF/LO there is no change in the voltage across load resistor.

    As you suggested, i checked the voltage across each capacitor which seems to be 2v across C1,C13 ; C6,C3,C7,C8, C11, C9- 5V AND C4, C14 - 0.4V 

    Idle current of the device is 256mA.

    I am not able to understand why still there is a voltage across load resistor when i am turning ON the supply.

  • Also after 2 hours the idle current of the board is displaying 160 mA 

  • Sir,  what should be the Rf and Lo power range if my operating frequency is 5.81 Ghz?