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So I have made a low pass filter and plotted the transfer function of it. However, I know I need to also use another opamp to correct the phase shifting/ gain. What design should be best to add on to the output so that it doesn't invert or change the transfer function, just shift it vertically? I have tried inverting and non inverting but both flip by graph. Help please?!? enter image description here

EDIT: This is what I tried, but it didn't just simply shift the graph (phase shift) but flipped it.

EDIT 2: Yes! I used the non-inverting op amp and it worked! I just accidentally had Vin/Vout instead of Vout/Vin. enter image description here

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  • \$\begingroup\$ Can you explain what you mean by shifting? Are you referring to amplitude or phase? What do you mean by "flip the graph along the Y-axis"? Does "shift it vertically" mean adding more gain in which case a non-inverting amplifier should work fine. I would like to help you but you are using non-standard terminology so I don';t know what you are trying to achieve. \$\endgroup\$ – Barry Oct 12 '19 at 1:00
  • \$\begingroup\$ Sorry about that, so I am referring to the phase of the graph. When I plotted the transfer function it created like an S curve. However when i tried to correct the gain by adding another op amp design the the end, the S curve was 'reflected'. I am looking for something that just shifts the S vertically without flipping. \$\endgroup\$ – Alicee Oct 12 '19 at 1:11
  • \$\begingroup\$ I see in your edited version that you tried an inverting amplifier which will do the flipping of the phase since its gain has a negative sign. In your original posting, ;you said you tried a non-inverting amplifier which should have worked. Can you post the schematic of that attempt so we can see what the problem is? \$\endgroup\$ – Barry Oct 12 '19 at 2:22
  • \$\begingroup\$ What, exactly, are you trying to achieve with your filter? This is far from clear in your post. \$\endgroup\$ – Chu Oct 12 '19 at 8:11
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I think that what you are saying is to "add gain" but not "invert" the signal. Your added amplifier is an "inverting" amplifier. You are "going into" the - input. So just use a "non-inverting" amplifier, "going into" the + input. Not sure of your experience level .... do you know how to do that? You can search for "non-inverting op amp amplifier" on a search engine. Otherwise, just ask and I or others will draw it for you !

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