Side-by-side comparison
| Parameter | Inverting | Non-Inverting Op-Amp |
|---|---|---|
| Input terminal used | Inverting (−) terminal | Non-inverting (+) terminal |
| Phase shift | 180° (signal inverted) | 0° (in-phase output) |
| Voltage gain formula | Av = −Rf/Rin | Av = 1 + Rf/Rin |
| Minimum gain magnitude | Can be less than 1 (attenuator) | Always ≥ 1 |
| Input impedance | Equal to Rin (e.g., 10 kΩ) | Very high, ~MΩ to GΩ range |
| Virtual ground concept | Inverting input held at virtual ground | No virtual ground; both inputs track |
| Summing capability | Directly extended to summing amplifier | Not directly used for summing |
| Common-mode rejection impact | Lower sensitivity to CM noise | Input signal appears as common-mode |
| Typical use case | Summing, integrators, DAC output stage | Buffer, sensor amplifier, voltage follower |
| Example IC | µA741, LM358 | µA741, TL071, LM324 |
Key differences
The inverting op-amp introduces a 180° phase flip and its input impedance is set entirely by Rin — typically 10 kΩ — which loads the source. The non-inverting configuration presents near-infinite input impedance, making it the right choice when source impedance is high. Gain in the inverting case can be set below 1 (e.g., Rf=5 kΩ, Rin=10 kΩ gives Av=−0.5), whereas non-inverting gain is always ≥ 1. For multi-input mixing, only the inverting topology supports a straightforward summing amplifier using the virtual ground node.
When to use Inverting
Use the inverting configuration when you need signal summation or must set gain below unity — for example, in a 4-input audio mixer built with an LM324 where each channel feeds through a 10 kΩ resistor to the virtual ground node.
When to use Non-Inverting Op-Amp
Use the non-inverting configuration when the source impedance is high or you need a unity-gain buffer — for example, connecting a piezoelectric sensor (output impedance > 1 MΩ) to an ADC input using a TL071 voltage follower.
Recommendation
For most sensor interface tasks in placement rounds, choose the non-inverting configuration; it preserves the source signal without loading it and requires no phase correction downstream. For signal processing chains that need mixing or integration, choose the inverting topology with a summing node.
Exam tip: Examiners frequently ask you to derive the gain expression for each configuration starting from the virtual short-circuit condition — practise this derivation fully, including the sign.
Interview tip: Interviewers at core companies expect you to explain why the inverting amplifier has finite input impedance equal to Rin and to calculate the output voltage of a two-input summing amplifier given resistor values.