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AD604 as front end

I am interested in use AD604 as the front end to an instrument, this instrument will work up to 1Mhz, I need lowest noise possible and Input Impedance of 20K

  • sorry, it looks I deleted the question:

    Do I need a 50 Ohms resistor at PAI to GND?

    Do I need an OPAMP in front of AD604?


  • Hi Carlos,

    It depends on the application. If you have a 50ohm source it usually means the source needs to be terminated, and this is shown in fig 52, for example. In this instance the source isn't shown, but a great many US transducers were once 50ohms.

    If your application isn't 50 ohms, or if it is terminated you may not need 50 ohms but you may need to terminate fo preserve waveform integrity. depending on the distance to the signal source.



  • Hi Jstaley:

    thanks for your answer, let me explain what I am trying to do:

    It is an instrument with a 2 o 3 feet coaxial cable probe, therefore length is not the problem, but I can not load the circuit I am measuring, therefore I am just guessing 20K will do, the measurements are from mV to 40 V rms, this are my questions:

    1. Can I add a decoupling capacitor in series to PAI to have just AC measurements?
    2. I see the input resistance is 300K, can I input the low voltage signal (+- 400mV) to be measured straight to PAI without an input resistor 
    3. For the higher voltages up to 40V rms can I just use a simple resistor divider? in order to be below the +-400mV?


  • This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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    EZ Admin