Transistor Suggestions for Differential Amp

Discussion in 'Analog & Mixed-Signal Design' started by sailmike, Jun 25, 2016.

  1. sailmike

    Thread Starter Member

    Nov 11, 2013
    143
    3
    Hi, I'm looking for transistor suggestions to use in a differential amplifier. I need a pair of N-channel MOSFET's or JFET's to use and could use some suggestions on which ones to use. The supply voltage will be 0 to 5 volts and the input signal will be around 100 to 300 mV not including any offset.

    Thanks a lot,
    Mike
     
  2. ifixit

    Distinguished Member

    Nov 20, 2008
    639
    108
    The 2N5564/65/66 dual FET would work for you depending on other factors that need to be considered.

    Ifixit
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,163
    1,796
    Is that all you got for requirements? That's not much to go on.
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,804
    The transistor you would use at 100 Hz are very different from 100 MHz. Other factors also need to be considered depending on your application.
     
  5. sailmike

    Thread Starter Member

    Nov 11, 2013
    143
    3
    Oh sorry forgot about that. The input signal will go up 100 kHZ.
     
  6. sailmike

    Thread Starter Member

    Nov 11, 2013
    143
    3
    The differential amplifier is part of an op-amp that will be used as one of two in a sample and hold circuit. The input for the sample and hold will go up to 100 kHZ. The rest of the op-amp works fine.

    The 2N5564/65/66 doesn't appear to be available. I checked Mouser, Digikey, and Newark for this part. Does anybody else have suggestions?

    Thanks,
    Mike
     
  7. RichardO

    Well-Known Member

    May 4, 2013
    1,238
    385
    Keep in mind that J-FET''s (and MOS-FET's) have very inexact threshold voltages. Because of this the amplifier will have a large amount input offset voltage. You can reduce this by either using a dual device or matching the J-FET's yourself.

    Are you building your own op-amp? :eek:
     
  8. sailmike

    Thread Starter Member

    Nov 11, 2013
    143
    3
    Yeah I'm required to design and build the op-amp from discrete components. So, doesn't anybody have suggestions?
     
  9. Papabravo

    Expert

    Feb 24, 2006
    10,163
    1,796
    It's not something that anybody besides a student would do. So it seems that you should pour over datasheets until you find one that is suitable. I would shortcut the process by using the search tools from Digi-Key or Mouser and finding one that was cheap and available. If it turns out not to meet the requirements at least you will have some ironclad justification for your choice. Who needs a design that can't be built and costs an arm and a leg on top of that. Relax -- you'll be fine regardless of your choice.
     
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