LMC7101: The output will be different with different LMC7101, the output change with the chip

Frank,

Please attach the schematic again. It is missing from the first post.

In what way is the output different? Do you have waveforms that show the diffrence?

Frank,

What is the desired function of this circuit?

The input AC voltage must be small because the input common mode is centered around 0V for a single supply.
The op amp output (pin 1) will be the greater of (Pin6+Vos) * 21 and 0V. This means the signal can be clipped at ground.
The level is clipping is variable based on Vos (input offset voltage).

If Vos is positive then all of the positive signal will be amplified and a small portion of the negative will be amplified.
If Vos is negative then none of the negative signal will be amplified and the lower part of the positive signal will not be amplified.

Therefore if the AC signal is very small and Vos is significantly negative and large then there will be no output.
If the AC signal is very large (>800mV) then parasitic diodes on the input could draw current making the input a clamp instead of a low pass filter.

Hi Ron,

The Vos should not influence the max value, becasue the output side has a DC block cap(high pass filter）. Now the phenomenon is sometimes the outuput is right, sometimes the output isn't right value, the gain will larger.

Thanks.
BR
Frank

Frank,

It is true that input caps block DC component of input and output caps block DC component of amplifier output.

Nevertheless,  Vos matters because the amplifier is not linear; the apparent gain changes with both Vos and input Vpp.

Is the goal to have a nonlinear amplifier that only amplifies part of the input signal?

Hi Ron,

Do you have some suggestions to improve the performance？ Thanks.

Br
Frank