Terminating a Single-Ended Input for ADA4940-1


I want to convert single - ended input to differential ended for driving ADC. I have gone through datasheet of ADA4940-1 in which calculations are given to terminate single ended input. For known source impedance I am using LTC6252 as buffer. But LTC6252's output impedance varies with frequency and my application is for different frequency ranging from 1MHz to 10MHz.

So how can I terminate single ended input for ADA4940-1 without using variable resistor?

  • 0
    •  Analog Employees 
    •  Super User 
    on Sep 16, 2019 5:50 PM

    Hi Explorer,

    The increase in output impedance of LTC6252 is pretty typical of most Op Amps. In most applications, the impedance balance discussion within ADA4940-1 datasheet is concerned with the low frequency value of impedance and not its high frequency behavior. Besides, a 50ohm impedance placed in series with LTC6252 output (as shown in ADA4940-1 Figure 66 below) will further reduce any impact of output impedance increase over frequency. In this case, the driver output impedance is considered to be 50ohm for the purpose of impedance balance calculations.

    Hope this answers your question.