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ADA4945-1 single-end input terminating from ADA4896-2 output

Category: Hardware
Product Number: ADA4945-1


I am going to use ADA4030-24 which prefer driver is ADA4945-1 and ADA4896-2 combination. The ADA4945-1 need to terminate a single-end input, and get a circuity as Figure-109 in the datasheet. But in my design, how could I define the Rs if the source of ADA4945-1 is from a ADA4896-2 output. If I can’t define the Rs, then I can’t get the Rt value.

Another question is if I don’t care the terminating, and use below LTSpice circuity to simulate. Then the ADA4945-1 differential output is double of the ADA4896-2 output. That make sense because Rf/Rg is 2. Why it has to terminate the single-end input? May I use my circuity in LTSpice without terminating? because the results looks good. Is there any risk?

figure 109 in datasheet:

figure 109 in datasheet

my LTSpice circuity :


  • Hi Shu,

    You should be getting the proper output on your 2nd case since most likely output impedance is not typically modeled on our part.

    On your first question, it is a source-load termination scheme especially when driving a line, or high speed signals are involved. But if you are driving the FDA directly, termination is not that needed. 

    Let me know if you have clarifications.



  • Thank you Goz. That make sense. I shall use my circuity in LTSpice without termination.

    It doesn't need termination if I use an amplifier to drive the FDA. Is it because the amplifier output impedance is very small? It doesn’t need to match impedance. But source-load is too large to ignore it for impedance match on high speed signal? Am I right?


  • Yup, exactly! You can check on Figure 36 below for the output impedance behavior of ADA4896 over frequency if it concerns your application.

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