Question 1

How do I calculate the gain of a non-inverting op-amp?

Accepted Answer

For an ideal non-inverting amplifier the closed-loop voltage gain is G = 1 + Rf / Rg, where Rf is the feedback resistor and Rg is the resistor from the inverting input to ground. For example Rf = 10 kΩ and Rg = 1 kΩ give G = 1 + 10 = 11, so a 1 V input becomes 11 V at the output.

Question 2

How do I calculate the gain of an inverting op-amp?

Accepted Answer

For an ideal inverting amplifier the gain is G = −Rf / Rin, where Rin is the input resistor. The minus sign means the output is inverted. With Rf = 10 kΩ and Rin = 1 kΩ the gain is −10, so a 1 V input gives −10 V at the output.

Question 3

What is the gain of a voltage follower (buffer)?

Accepted Answer

A voltage follower has the output tied directly to the inverting input, so its ideal gain is exactly 1 (0 dB) and the output equals the input. It is used as a buffer to drive a low-impedance load from a high-impedance source without loading it down.

Question 4

How do I convert a voltage gain to decibels?

Accepted Answer

Voltage gain in decibels is GdB = 20 × log10(|G|), using the magnitude of the gain. A gain of 11 is about 20.83 dB, a gain of 10 (or −10) is exactly 20 dB, and a gain of 1 is 0 dB.

Question 5

Why does the real gain differ from this ideal calculation?

Accepted Answer

This calculator assumes an ideal op-amp with infinite open-loop gain and input impedance. A real device has a finite gain-bandwidth product, slew-rate and offset, and the output clips near the supply rails. At high frequency or large signals the actual gain falls below the ideal closed-loop value.

Op-Amp GainCalculator

Op-Amp Gain
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