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I was tasked to make 4 processes using operational amplifiers: adding, substraction, multiplication, and division.

However, only the add and substract operations work: whenever I try to multiplicate or divide MultiSim shows very different values to those I am expecting.

Note: On the multiplication circuit I have already tried to use the anti-log circuit first before actually using an inverted buffer, yet both times the result is still not what I expected (in this case, 15). Note that V1 is 5 V and V2 is 3 V.

enter image description here

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  • \$\begingroup\$ Welcome to the site! Since you have issues only with multiplication and division, can you show us what you tried with only those only? You dont need to post the whole schematic of multisim. That way we will know which one of those schematics you are looking at/having issues with. I cannot understand which of the circuits I am seing, are the ones you say you have an issue with. \$\endgroup\$
    – Christianidis Vasilis
    Commented Sep 18, 2022 at 5:32
  • \$\begingroup\$ Note that at +/-50V you are far exceeding the maximum supply voltages for the TL084 opamps. \$\endgroup\$
    – GodJihyo
    Commented Sep 18, 2022 at 5:39
  • \$\begingroup\$ @ChristianidisVasileios I have edited the image so that it fits both circuits I'm currently struggling with \$\endgroup\$
    – JCorona98
    Commented Sep 18, 2022 at 6:41
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    \$\begingroup\$ JC98, perhaps the first thing I'd do is replace the diodes with diode-connected BJTs. You'll get better linearity (logwise) over more orders of magnitude, that way. Use the default NPN, in fact. Should be 'better.' (Not perfect.) \$\endgroup\$
    – jonk
    Commented Sep 18, 2022 at 6:51

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Note that your inputs are a bit "too high" (should work, but ...).

Log amplifier can work better if you add "offset" correction as in this circuit (NB op-amp are J-Fet input amplifiers).

enter image description here

As @Jonk pointed out, here is a log circuit dealing with quasi 7 decades.
Ok, a bit complicated in the real world, but it works.

Note that the "division" operator is made with this "log" circuit placed in the "feedback" loop of an op-amp. See "Analog Devices" applications.

enter image description here

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