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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    •  Analog Employees 
    on May 7, 2018 7:45 AM

    Hi,

    You would at least need an amplifier with a THD of -72 dBc at fin= 5 MHz,  a much faster op amp would do so. Here are the possible choices: LTC6268/LTC6269, and ADA4857. Take note that ADA4857 runs at 5V and LTC6268/9 can run at 3.3 V. Also, reconsider your design. LTM9008-14 is specified to accept a differential input voltage of 2 Vpp. In your current schematic, you're running it at 4.8 Vp-p differential.

    Regards.

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  • 0
    •  Analog Employees 
    on May 7, 2018 7:45 AM

    Hi,

    You would at least need an amplifier with a THD of -72 dBc at fin= 5 MHz,  a much faster op amp would do so. Here are the possible choices: LTC6268/LTC6269, and ADA4857. Take note that ADA4857 runs at 5V and LTC6268/9 can run at 3.3 V. Also, reconsider your design. LTM9008-14 is specified to accept a differential input voltage of 2 Vpp. In your current schematic, you're running it at 4.8 Vp-p differential.

    Regards.

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