# Non-Inverting Op Amp

## What is a Non-Inverting Op Amp?

### Definition

A non-inverting op amp is an operational amplifier circuit with an output voltage that is in phase with the input voltage. Its complement is the inverting op amp, which produces an output signal that is 180^{o} out of phase.

### What is a non-inverting input?

An amplifierâ€™s non-inverting input refers to the pin configuration. The non-inverting input is the terminal marked with a plus (+) sign, and the inverting input is marked with a minus (-) sign. These can also be referred to as positive and negative terminals.

### What is the formula for a non-inverting amplifier?

Non-inverting op amps work following the op amp golden rules:

- The Current Rule: No current flows into the inputs of the op amp (I
_{+}=I_{-}=0). - The Voltage Rule: The output of the op amp attempts to ensure that the voltage difference between the two inputs is zero (V
_{+}=V_{-}).

Consider the non-inverting op amp circuit shown above. According to the Voltage Rule, the voltage at the inverting (-) input will be the same as at the non-inverting (+) input, which is the applied voltage V_{in}.

The current going through R_{1} can then be given as V_{in}/R_{1}.

According to the Current Rule, the inputs draw no current, so all that current must then flow through R_{2}.

The output voltage can then be given as V_{out}=V_{in}+(V_{in}/R_{1})R_{2}.

The gain is then V_{out}/V_{in}=1+(R_{2}/R_{1}).

The gain will never be less than 1, so the non-inverting op amp will produce an amplified signal that is in phase with the input.

### What is the difference between an inverting and non-inverting amplifier?

A non-inverting amplifier produces an output signal that is in phase with the input signal, whereas an inverting amplifierâ€™s output is out of phase. Both the inverting and non-inverting op amps can be constructed from one op amp and two resistors, just in different configurations.