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I'm new to op-amp (and circuits in general) and I'm trying to amplify a voltage signal with a simple op-amp circuit such as this one. However, as I increase the gain (increase R2 and/or decrease R1), the signal starts to level shift upwards until it hits the upper rail and I'm no longer able to see any of the gained oscillation. The shift is gradual, but the signal hits the 5V rail (becoming just a straight line) once the gain is around 1000. Could someone explain what may be causing this and possible solutions? Everything online just refers to the basic equations (A = 1+r2/r1. A = -r2/r1, etc), but nothing explaining a "Vout = A*Vin + shift" effect.

Some more details:
I'm using MCP6021 RRIO op-amp with +/-5V rails. The original signal is centered at 0. To clarify, I'm not referring to phase offset, but an offset of the amplitude center of the signal. I'm trying both non-inverting and inverting, and ran into the same problem. The circuit I'm testing with is non-inverting, wired exactly same as the example in the screenshot. The other screenshots are of the oscilloscope with no gain, 10 gain, 100 gain, and 1000 gain respectively.

schematic

No Gain

Gain = 10

Gain = 100

Gain = 1000

yuki
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    Show a schematic of exactly how you have everything hooked up, and show scope shots of input and output, or at least a drawing of your input signal. Do you have a negative rail for your op-amp? If not, how do you expect to amplify a signal that's centered at 0 V? – John D May 23 '23 at 17:54
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    If you're using -5 to +5v, then the op-amp output will never go beyond -5 to +5v; those are the "rails" to which it is limited. If you need it to go to +10v, then you'll have to supply +10v; assuming that particular opamp can handle it (not all can.) – rdtsc May 23 '23 at 18:14
  • Are you sure your input signal is exactly centered at zero volts? With a gain of 1000 you'd only need 5 mV of offset to rail the output. Can you try AC coupling your signal with a capacitor? – John D May 23 '23 at 18:18
  • @JohnD It does have a negative rail (-5 to +5). I included more photos to show what I'm doing. – yuki May 23 '23 at 18:29
  • @JohnD good point I had not thought of a minor offset causing this. Could you elaborate more on how AC coupling with a capacitor might help? – yuki May 23 '23 at 18:40
  • AC coupling will remove any DC offset in your input signal. If you do AC couple in the circuit shown, be sure to put a high value resistor from the + input to ground to provide a path for bias currents. See here: https://electronics.stackexchange.com/questions/652108/why-do-we-need-r1-in-a-non-inverting-op-amp – John D May 23 '23 at 18:51
  • @JohnD thank you, this seems to have helped - just need to figure out how to offset the voltage drop from the added resistor from AC coupling - I am at least able to see the signal now when gained 1000 – yuki May 23 '23 at 20:31
  • The input current of this Cmos opamp is almost zero. but its input offset voltage listed ON ITS DATASHEET can be from -0.5mA to +0.5mV which is amplified by the opamp. – Audioguru May 23 '23 at 21:08

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