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I was doing some LTSpice simulation with an op-amp to amplify a 1 millivolt 40 kHz sine wave. However, in the output signal, it had just raised the voltage of the whole waveform, it decreased the amplitude. The amplitude now was under 500 microvolts. I was expecting it to only increase the amplitude of the signal.

schematic

waveform

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  • \$\begingroup\$ You appear to be injecting an AC (both positive and negative) signal into a non-inverting input. What's your thinking about what should happen when the input signal goes negative? \$\endgroup\$
    – Transistor
    Commented Jan 6 at 12:25
  • \$\begingroup\$ The LT1001 is nowhere near capable of working rail to rail. And according to the datasheet "The LT1001 is specified over a wide range of power supply voltages from ±3V to ±18V" \$\endgroup\$
    – Finbarr
    Commented Jan 6 at 12:33
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    \$\begingroup\$ kudos to LT for properly modeling the opamp wrt supply voltage ;) \$\endgroup\$
    – bobflux
    Commented Jan 6 at 12:35
  • \$\begingroup\$ @Finbarr It works with lower voltages too if you have enough gain like in this circuit. \$\endgroup\$
    – Justme
    Commented Jan 6 at 12:43

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First of all, since you are giving it a 0V and 3.3V supply, an input of signal around 0V or even negative are invalid.

It would need a negative supply to handle signals near 0V.

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  • \$\begingroup\$ How do I give it a negative supply? Should I feed 5V into an inverting amplifier and use the output? \$\endgroup\$
    – epicMan123
    Commented Jan 6 at 12:47
  • \$\begingroup\$ @epicMan123 Change the negative supply pin, which you have now connected to 0V ground, to a supply that gives the opamp a negative voltage. Just like you have a supply for positive voltage already. Try giving it more voltage like +/- 10V. \$\endgroup\$
    – Justme
    Commented Jan 6 at 12:54
  • \$\begingroup\$ I changed the power supply to 10V but the problem still persists. The amplitude is still millivolt level. \$\endgroup\$
    – epicMan123
    Commented Jan 6 at 13:03
  • \$\begingroup\$ @epicMan123 It sounds like you only changed the 3.3V to 10V. I don't know if you gave it a negative supply. I can't see what errors you have. \$\endgroup\$
    – Justme
    Commented Jan 6 at 13:16
  • \$\begingroup\$ Took a bit of thinking but I got it now. I made a new 5V voltage supply and labeled the + as ground and wired the - to the op-amp's negative supply. Thanks for the help! \$\endgroup\$
    – epicMan123
    Commented Jan 6 at 13:42

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