amplificateur d'instrumentation

Discussion in 'The Projects Forum' started by azerty1, Jan 22, 2014.

  1. azerty1

    Thread Starter New Member

    Apr 30, 2013
    I want to simulate the circuit seal it and I want to determine the differential and the common gains and the CMRR by simulation. for that i must apply all the equations of these parameters on the same assembly or there is a specific way to do it.
    thank you...
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
    I think -5 volts supply at Pin 4 is connected wrong.
  3. azerty1

    Thread Starter New Member

    Apr 30, 2013
    no, i connecte V- to -5V.
    and i want to know how can i gate a differential and common gains in function of frequency
  4. John P

    AAC Fanatic!

    Oct 14, 2008
    If "amplificateur d'instrumentation" means instrumentation amplifier, you'd do better to use a purpose-made component rather than an op amp. Try the AD623, for instance.
  5. LvW

    Active Member

    Jun 13, 2013
    azerty1, for the two inputs V1 and V2 the output voltage is


    This assumes R1=R3 and R2=R4 (as shown in your diagram).

    Thus, the differential gain is 100 and you must choose the input difference (V2-V1) accordingly - without driving the output into saturation.

    For simulation of the common mode gain and CMRR you must be aware that the resistor tolerances have a considerable influence on the result (because of the requirement R1=R3 and R2=R4).
  6. nigelwright7557

    Distinguished Member

    May 10, 2008
    It isn't wired up as a differential amp but if it was the gain would be 100 times difference in input voltages.

    The inputs should be to R2 and R3.