ADMV1014 IF filter - must it be reflectionless?

Hello EZs,

I'm designing a PCB using the ADMV1014. I don't require a large IF bandwidth so don't really care about anything above 300 MHz, therefore am putting a low-pass filter on the I and Q differential outputs. 
My current filter choice (Mini-Circuits' LFCG-320+) is reflective in its stopband (500 - 6000 MHz) - what will happen when most of the output power at frequencies above 300 MHz is reflected back to the ADMV's I_P, I_N, Q_P and Q_N pins? Is this okay, or should I get a reflectionless filter?
Cheers
Joe
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  • +2
    •  Analog Employees 
    on Dec 2, 2019 6:42 PM over 1 year ago

    Hi Joe,

    If your Baseband Bandwidth (I'm assuming you're using IQ Mode) is up to 300MHz then I would be concerned about the 2*RF-8*LO (LO frequency referenced from ADMV1014 LO ports) frequency at 600 MHz. The datasheet spur table suggests that this would be approximately 60dBc lower than the main baseband output. Even so the Mini Circuits filter has a very poor VSWR (~12) at 600MHz and all the power at 600MHz will be reflected back into the part. If you already have these filters then I would strongly recommended adding a 3dB or even better 6dB attenuator in line between the filter the and IQ pins. 

    Thanks,

    Taz

Reply
  • +2
    •  Analog Employees 
    on Dec 2, 2019 6:42 PM over 1 year ago

    Hi Joe,

    If your Baseband Bandwidth (I'm assuming you're using IQ Mode) is up to 300MHz then I would be concerned about the 2*RF-8*LO (LO frequency referenced from ADMV1014 LO ports) frequency at 600 MHz. The datasheet spur table suggests that this would be approximately 60dBc lower than the main baseband output. Even so the Mini Circuits filter has a very poor VSWR (~12) at 600MHz and all the power at 600MHz will be reflected back into the part. If you already have these filters then I would strongly recommended adding a 3dB or even better 6dB attenuator in line between the filter the and IQ pins. 

    Thanks,

    Taz

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