# OpAmp gain calculator

### Inverting op-amp

As the name suggests this configuration of the op-amp will invert the signal given on the input terminal. For that, the signal is given to the inverting terminal.

Now let’s understand the logic behind the inversion of the input signal. If you know the op-amp wants to keep the voltage on both terminals the same. The non-inverting terminal connects to the ground (0 volts).

So op-amp will want inverting terminal also to be at ground. But there is an input signal at the inverting terminal. So op-amp will have to set its output such that the voltage on the node ‘x’ should be 0 volts.

Input resistor Ri and feedback resistor Rf are acting like voltage dividers and diving the voltage between the input voltage and output voltage. The divided voltage is being fed to inverting terminal. So voltage on the inverting terminal will be voltage divided between the input voltage and output voltage and it should be zero. So op-amp should change the output voltage according to the input signal.

For example, design an op-amp inverting amplifier that has a gain of 1. So if a 1v signal is applied then the output will be -1v. Then it will cancel the input voltage.

Rin = ∞

Ii = If

So, the formula to calculate the gain of inverting op-amp is Rf/Ri.

### Non-inverting op-amp

Here input signal doesn’t get inverted. The signal is given to the non-inverting terminal. Here also, the amplification concept is the same. Op-am will want that both input terminals should be on the same potential. So let’s consider that Ri and Rf are the same. So it will divide the output voltage in half at node ‘x’.

If a 1-volt signal is applied then the output will be 2 volts. Half of the output voltage which is 1 volt will be applied to inverting terminal. This way potential on both terminals is the same.

Now you can understand that we change the gain by changing the resistor values.

So, the formula to calculate the gain of the non-Inverting op-amp is 1+Rf/Ri.

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