+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Junior Member level 1
    Points: 1,143, Level: 7

    Join Date
    Feb 2008
    Posts
    15
    Helped
    0 / 0
    Points
    1,143
    Level
    7

    voltage follower unknown OA

    Hello all,
    i would like to build a voltage follower. I found the scheme (see the attachment). Unfortunately, I am not able to get neither LM102 nor LM107. It seems they are obsolete.
    What other ICs shall I use. I need to track, as accurately as possible, 2 differential signals, 60kHz, +-100mV.
    Shall I employ bipolar of JFET operational amplifiers?

    Thank you guys in advance,
    regards Meereck

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 40,458, Level: 49
    Achievements:
    7 years registered
    LvW's Avatar
    Join Date
    May 2008
    Location
    Germany
    Posts
    5,790
    Helped
    1729 / 1729
    Points
    40,458
    Level
    49

    Re: voltage follower unknown OA

    If you need an instrumentation amp as shown in your circuit diagram you can, in principle, use any unity gain compensated opamp.
    As the input opamps are unity gain followers, itīs off less importance if they are equipped with BJT or FET input stages. However, of great importance are exact resistor values of the output stage.
    Because of good accuracy at a frequency of 60 kHz the GBW should at least be (3..5) MHz. But donīt forget the slew rate.



    •   AltAdvertisement

        
       

  3. #3
    Junior Member level 1
    Points: 1,143, Level: 7

    Join Date
    Feb 2008
    Posts
    15
    Helped
    0 / 0
    Points
    1,143
    Level
    7

    Re: voltage follower unknown OA

    Quote Originally Posted by LvW
    If you need an instrumentation amp as shown in your circuit diagram you can, in principle, use any unity gain compensated opamp.
    As the input opamps are unity gain followers, itīs off less importance if they are equipped with BJT or FET input stages. However, of great importance are exact resistor values of the output stage.
    Because of good accuracy at a frequency of 60 kHz the GBW should at least be (3..5) MHz. But donīt forget the slew rate.
    Hi, thank you for a fast and useful reply.

    Any examples of OA which is unity gain compensated?

    Have a nice day. Meereck



    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 5
    Points: 40,458, Level: 49
    Achievements:
    7 years registered
    LvW's Avatar
    Join Date
    May 2008
    Location
    Germany
    Posts
    5,790
    Helped
    1729 / 1729
    Points
    40,458
    Level
    49

    Re: voltage follower unknown OA

    Another comment:
    Donīcare about the 1 kOhm resistor for offset trimmming. It can be removed.
    If you select an opamp with sufficient small offset voltage (say 0.1 mV) such a balance circuitry is not necessary because of the resistor tolerances of the output stage.



--[[ ]]--