Differential driver, Differential input, made with OpAmps

Discussion in 'The Projects Forum' started by kender, Jul 30, 2011.

  1. kender

    Thread Starter Senior Member

    Jan 17, 2007
    263
    0
    Folks,

    I’m designing an analog circuit that should take a voltage from a pot, remove offset, output 2 complementary analog voltages. The circuit has both positive and negative supply rails, but the lower end of the pot should be grounded. Signals are DC. Low output impedance would be nice.

    I have an idea about how to achieve this with 2 instrumentation amps. Here’s the schematic

    [​IMG]

    But I wonder, is there’s a more elegant way of achieving this with 2 or so OpAmps?

    Any suggestion, insight or reference is really appreciated!

    Cheers,
    - Nick
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,107
    3,038
    A quick read of the datasheet is my only reference, but your circuit looks like it would work. Make sure to think about what "ground" is, for the signal and the power supply.
     
  3. kender

    Thread Starter Senior Member

    Jan 17, 2007
    263
    0
    Well, I knew that the circuit in the O.P. works. At the same time, I don't like it, because it uses InAmps. So, I wonder if there's a descent OpAmp circuit for this. That's the main question of the O.P.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I don't know why you dislike instrumentation amplifiers? It's folly to try to "roll your own" using opamps & resistors, because you will have a dickens of a time trying to get the thing balanced. Even if you're using 0.1% resistors, you still won't match the CMRR of an instrumentation amplifier; the latter are laser-trimmed at the factory.

    An instrumentation amplifier has a far higher input impedance than a fully differential opamp, which is great for accuracy and stability. A fully differential amp is better for generating precise differential outputs.

    So, you're using a couple of instrumentation amplifiers to produce a differential output; it has the advantages of both, but with the disadvantage of increased cost.

    If you're going to try this, It would be best to use a dual instrumentation amp package so that both amps will be at the same temperature, and the gain resistances will obviously need to be matched very closely.
     
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