# amplificateur d'instrumentation

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

1. ### azerty1 Thread Starter New Member

Apr 30, 2013
15
0
hello,
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...

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2. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,515
515
I think -5 volts supply at Pin 4 is connected wrong.

3. ### azerty1 Thread Starter New Member

Apr 30, 2013
15
0
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
1,638
225
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
674
100
azerty1, for the two inputs V1 and V2 the output voltage is

V,out=(V2-V1)*R2/R1=(V2-V1)*100.

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 Senior Member

May 10, 2008
488
71
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.