Ganho op-amp não-inversor

Non-inverting op-amp gain

In a non-inverting amplifier the input signal goes straight to the op-amp's non-inverting (+) pin. The feedback resistor Rf runs from the output back to the inverting (−) pin, and R1 ties that (−) pin to ground. Assuming an ideal op-amp, the closed-loop gain works out to Av = 1 + Rf / R1, so Vout = Vin · (1 + Rf / R1). The output stays in phase with the input, and notice the gain is always ≥ 1. This topology can't attenuate. Set Rf = 0 (short) and R1 = ∞ (open) and the whole thing becomes a unity-gain buffer (voltage follower) with A_v = 1. As an example, Rf = 9 kΩ with R1 = 1 kΩ gives a gain of 10, so a +0.5 V input comes out as +5 V. Input impedance is essentially that of the op-amp itself (often MΩ to GΩ), which is why it suits high-impedance sources so well.

Applications: buffers, sensor front-ends, audio gain stages

Wherever you need high input impedance, the non-inverting topology tends to show up. Think unity-gain buffers that match impedance between stages, sensor front-ends like pH probes, piezoelectric pickups and electret microphones, the input stage of an instrumentation amplifier, or class A/AB audio gain stages that have to keep signal phase intact. You'll also find it in active filters such as Sallen-Key low-pass and high-pass designs, and as the gain stage that sits after a passive RC anti-aliasing filter feeding an ADC.

FAQ

Why can't gain be less than 1? In 1 + Rf/R1, the smallest value you can reach is 1, when Rf = 0. The input voltage itself sets the floor. If you need to attenuate, reach for an inverting stage or a plain divider.

What about input impedance? It matches the op-amp's open-loop input impedance, which is usually very high, anywhere from MΩ to TΩ, so the circuit barely loads the source.

How do I make a voltage follower? Short the output straight to the (−) pin (Rf = 0) and leave R1 open (∞). That fixes the gain at exactly 1.

Does it invert the signal? No. The output stays in phase with the input, which is exactly what you want in signal chains that care about phase, like audio or AC measurement.