Low bias current bipolar op amps?

Discussion in 'General Electronics Chat' started by bitrex, Apr 26, 2010.

  1. bitrex

    Thread Starter Active Member

    Dec 13, 2009
    Can anyone recommend a cheap op amp with relatively low input bias current specs? Bipolar input would be preferred to get the lower offset voltage as well. Linear technology makes some JFET input op amps with fantastic specs on both, but they're all like $4 each in small quantities - too expensive. :(
  2. JDT

    Well-Known Member

    Feb 12, 2009
    If you want low offset voltage, bipolar input is the only way to go.

    As far as price goes:- You get what you pay for!

    A lot of manufacturers have a "tree" or a table on their websites where you can compare specs and prices.
  3. peranders

    Well-Known Member

    May 21, 2007
    AD8610 is very nice. I have an item with 20 uV
  4. kkazem

    Active Member

    Jul 23, 2009
    One of my favorites is the ON-Semi (formerly Motorola) MC34072A series. It comes in single. dual, and quad versions. works equally as well on single supply and split supplies, and has a low input bias current of 500 nA typical (that's 1/2 uA). It is a bipolar, has 13.5 V/uSec slew rate, and a gain-bw product of 4.5 MHz, and it operates from 3V up to 44V supply. Its input offset voltage is 3.0 mV max for the "A" suffix versions. Overall, it is a great, general purpose op-amp. If you additionally need lower input offset voltage, the single version has two pins brought out that connect to an external pot for zeroing-out the input offset voltage. These units cost about $ 1.12 at DigiKey for the single version in an SMT package. There are thru-hole dip packages, but they are in short supply right now and are harder to find and are more expensive due to the current shortage. Please see the attached ON-Semi complete datasheet for the series in pdf format.

    Good luck.
    Kamran Kazem
  5. bitrex

    Thread Starter Active Member

    Dec 13, 2009
    Thanks for the recommendations, everyone.
    Those specs look good, except...is 500 nA really that low of a bias current for a bipolar? I think even the humble LM324 has something like 150 nA, max. Otherwise it is one I will keep in mind!