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ADRF6755 Baseband IQ Input signals are attenuating when connected to ADRF

Yuktheshwar
on Sep 29, 2020

Hi,

We are generating the I,Q differential signals at the required level 540mv DC mean and 280mv P-P on each line.

But when we connect the these 4 lines(I+,I-, Q+, Q-) to ADRF, all these four signals are loading and changing values to 540mv  mean and 180mv P-P

We tried giving them to 450mv P-P also, still they are attenuating.

What could be the reason? How can I resolve this?

Regards

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  • 0
    •  Analog Employees 
    on Oct 6, 2020 8:29 PM

    Hi,

    Baseband inputs of ADRF6755 are high impedance (30Kohm at 1MHz, roll off at higher frequency) and it should be driven from a low impedance source. Then the voltage swing level on the source is driven to baseband inputs on ADRF6755 fully. If the source impedance is not low enough compared to the input impedance, the driven voltage to ADRF6755 will be down by voltage divider. And  we recommend the dc bias level at 500 mV +/- 25mV. 

    Please refer to "Baseband Inputs" section on page 24 in datasheet.

    Thanks

    Tony

  • 0 on Oct 9, 2020 4:28 AM in reply to THA
    Hi Tony,
    Thanks for the reply,
    I am using a current based DAC which can produce a 1.125mA to 3mA DAC current.
    I configured it 1.1.25mA and followed configurations shown in "Figure 62. Typical Baseband Input Configuration". To match my current ratings, I have used 500 Ω resistor instead of 50ohm.1kΩ instead of 100 Ω. Do you suggest using a 100 Ω resistor in place of a 1 kΩ resistor?  
    Pl advice. 
  • +1
    •  Analog Employees 
    on Nov 25, 2020 9:33 PM in reply to Yuktheshwar

    Hello,

    Sorry for late. 1Kohm in place of a 100 ohm in FIGURE 62 will match to the differential 2* 500 ohm termination resistors.

    Make sure if DAC in use meets the output common mode range with 1.125 mA and 499 ohm.

    Thanks

    Tony 

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