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LMP2022

marc windels1
Prodigy 20 points
Other Parts Discussed in Thread: LMP2022

For any linear amplifier with 2 inputs V1 and V2 : output  V0=A1V1-A2V2+Constant.

For an opamp A1 >0   A2 >0   A1approximately = A2  but A1can  be < A2 or A1 >A2

If we define : Vcm=(V1+V2)/2 and Vd = V1-V2 then V0= A1.(Vcm+Vd/2) - A2.(Vcm-Vd/2) +Constant   or

V0=(A1-A2).Vcm + Vd/2.(A1+A2)+Constant = Acm.Vcm+Ad.Vd+Constant

So, the common mode gain Acm = A1-A2 can be >0 or <0 and CMRR = Adm/Acm can be >0 or <0.

Do you agree with this conclusion?

Of course CMRR in db = 20.log( absolute value CMRR) always >0

For a dual output LMP2022, I suppose that the polarity of the CMRR of each half LMP2022 is independant of the polarity of the other half LMp2022?

Do you agree with this conclusion.

I need to know because in my circuit an output is dependant on the difference of both CMMR.

An other output is dependant on the sum of both CMRR.

Thank you for your effort.

Marc Windels

  • 0
    Expert 1220 points

    The generic terms look ok to me, but the real question you are asking is the matching of the outputs.
    As far as I know, manufactures *do not* guarantee matching of a dual, triple, or quad op-amp. Each channel is independent of one another and it guaranteed to be in spec according to the datasheet.
    In the old days, laser trimmed op-amps would be well within spec and really tight, but after the package molding cures, the mechanical stress changes the Vos. TI has eTrim, so maybe they can match channel to channel now or at least will look at it.
    I would suggest to do a worst case analysis (assume all errors are positive or negative and sum them together). An RSS method would be realistic, but that is best left for you to decide what your application can handle.

    -Ken