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Both the inverting amplifier and non-inverting amplifier use negative feedback. Both provide gain. But one inverts the signal while the other does not. How to know which one to use? Are there applications where only one of the two can be used (provides both positive and negative supplies exist)?

Is it true that single supply op amp can only create non-inverting amplifier?

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  • \$\begingroup\$ It depends on what the desired functionality is. Do you want the signal inverted or not? \$\endgroup\$ – PlasmaHH Feb 16 '16 at 13:31
  • \$\begingroup\$ This is a general question. When does it matter if the signal should be inverted or not? Inversion means 180 deg phase shift. I don't think it matters in audio applications. I wonder where it does matter. \$\endgroup\$ – quantum231 Feb 16 '16 at 13:33
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    \$\begingroup\$ Isn't that basically answered by this question already? electronics.stackexchange.com/questions/37227 \$\endgroup\$ – PlasmaHH Feb 16 '16 at 13:44
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    \$\begingroup\$ I'd be more careful with the generalization "Inversion means 180 deg phase shift", because it actually doesn't mean that. It just looks like it does if your waveform is continuous & symmetrical. A real phase shift requires some time delay. \$\endgroup\$ – brhans Feb 16 '16 at 14:41
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There are a couple reasons (at least) for choosing a particular configuration:

  1. If you need a high input impedance, then you are forced into a non-inverting configuration. This is commonly required in a buffering situation. An inverting configuration has an input impedance equal to the input resistor which may load the source circuit.

  2. If you need a summing amplifier, then inverting is the way to go as the inverting input is the summing junction.

Is it true that single supply op amp can only create non-inverting amplifier?

No. With a DC offset (on the non-inverting input) you can have an inverting configuration although the input signal will need to be ac coupled under most circumstances.

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There are some specific applications which require (a) non-inverting or (b) inverting gain stages. This is true - in particular - for active filters and harmonic oscillators.

  • Examples to (a): Sallen-Key-filter stages; WIEN type oscillators.
  • Examples to (b): Multi-feedback filterstages (MFB); Phase-shift oscillators.
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You must always connect both input terminals of an opamp to thought-out and considered points. What you connect them to determines what function the opamp will provide.

If you connect +ve to a ground, and -ve via a feedback impedance to the output terminal, you create a 'transimepdance amplifier'. Any current you now push into the -ve input must also be balanced by a current from the output terminal through the impedance. Use a feedback resistor to convert current to volts. Use a feedback capacitor to create an integrator. The gain will be inverting.

If you connect your input voltage to +ve, and the -ve to a fraction of the output voltage (create a fraction with a voltage divider to ground, usually resistors, but you could use other impedances or even a transformer), you create a non-inverting amplifier, where the gain is the reciprocal of the feedback voltage divider.

You can do more complicated things as well, but the two above are the basics.

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