Fully differential current integrator.

Discussion in 'The Projects Forum' started by Filippo, Apr 13, 2012.

  1. Filippo

    Thread Starter New Member

    Apr 13, 2012
    Hi everyone,
    working through my project that consists in developing an integrated analog circuit for the readout of a sensor I'm now facing a new problem: how to fix the common mode input voltage of a fully differential amplifier that must work as a current integrator.
    To be more precise: the fully differential is set with the two feedback capacitors for the integration, and there is a current signal source (that is the drain pin of the output mos of the sensor, whose voltage is not defined).
    If anyone did understand or at least have an idea about the problem please let me know.Thanks

    (The description is probably not so clear so for any doubt don't hesitate to ask)
  2. jimkeith

    Well-Known Member

    Oct 26, 2011
    1. First, add load resistor to current source output.
    2. If this load resistor may be grounded the problem is simplified and no differential amplifier is required.
    3. If it cannot be grounded, measure voltage across resistor with a basic differential amplifier.
    4. Then integrate the voltage signal from either #2 or #3 above with an integrating amplifier
    5. If necessary, the voltage output may be converted again to a current source via an additional op amp

    All this should be easily accomplished with a dual or quad op amp
  3. Filippo

    Thread Starter New Member

    Apr 13, 2012
    Thanks for the advide but I have the need to integrate the current and not a voltage; with voltage I wouldn't have any problem. Anyway just yesterday I found a solution that seems to be working; need to test a little bit more.