I am designing a circuit for driving a differential input ADC. As operational amplifier I use LTC 6254. My design works fine when simulating in LT Spice. However, when it comes to analyzing one of my outputs using a spectrum analyzer voltage level collaps

I simulated my circuit in LTSpice, as the spectrum analyzer I placed 50 ohm resistors. It works fine. 

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  • Yes my input signal is always below 5MHz.
    I have looked through the differential amplifiers you suggested  AD8139,    LTC6404-1,  ADA4940,  LT1994.
     
    One other requirement in my design is that the input source is a high impedance source and can only drive capacitive loads of ~15pF.
     
    Therefore I require the configuration I send in the above schematics. 
     
    1) Is it possible to drive the amplifiers you suggested in a similar way?
     
    I will check my circuit again about the 50 ohm load driving problem.
     
    thanks
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  • Yes my input signal is always below 5MHz.
    I have looked through the differential amplifiers you suggested  AD8139,    LTC6404-1,  ADA4940,  LT1994.
     
    One other requirement in my design is that the input source is a high impedance source and can only drive capacitive loads of ~15pF.
     
    Therefore I require the configuration I send in the above schematics. 
     
    1) Is it possible to drive the amplifiers you suggested in a similar way?
     
    I will check my circuit again about the 50 ohm load driving problem.
     
    thanks
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