I think that with pictures will be more easy:
2) Signal before R7 and R8:
3) Signal pin 2 and pin 3
4) Output pin 6
I need to know why the signal is assimetric? Can you help me please.
Thanks in advance.
It's hard to tell what the output should be with the scales shown on the scope shots. What is the amplitude of the differential input to the AD623? What is VCC2 and where have you set REF2?
It is also hard to see what the common-mode voltage at the inputs is during your pulse excursions. Can you elaborate what the input voltage levels to AD623 are? You might check the equations in the "Input Differential and Common-Mode Range..." section of the datasheet to make sure these voltages are within range. These equations are also embedded in a Diamond Plot tool, which you can check to see if there is a saturation/headroom issue.
It seems that the AD623 output is saturated near ground for the negative excursions of the waveform. It may want to go farther, but it cannot due to the output range limitation. Something similar may be happening for the positive side as well, depending on answers to the above questions. Have you tried removing D5 to see if there is any effect? Also if you adjust P1, does the maximum of the AD623 output waveform change accordingly or does it stay in the same place?
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