Non-inverting Amplifier

A non-inverting amplifier produces an amplified signal which has the same polarity as the input signal using only an op-amp IC plus two external resistors

The output voltage is determined by the external resistors and the input voltage according to the following equation:

Equation: Vout = Vin x (1 + R2 / R1)

The voltage gain AV is given by Vout / Vin, which may be found by rearranging the above expression:

Equation: Av = Vout / Vin  = 1 + R2 / R1
The minimum voltage gain of this circuit is unity, unlike the inverting amplifier which can have a voltage gain either larger or smaller than one. The non-inverting amplifier also benefits from a much higher input impedance than the inverting amplifier.

Example 1

Calculate the voltage gain of an non-inverting amplifier with resistors R1 and R2 = 1 kΩ and 10 kΩ respectively.
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AV = 1 + R2 ÷ R1

  = 1 + 5,000 ÷ 1,000

  = 6

The voltage gain is a number and does not have a unit.

Example 2

Calculate the output voltage produced by a non-inverting amplifier if resistor R1 = 1 kΩ, feedback resistor R2 = 4 kΩ, and the input voltage is +2 V.
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Vout = Vin × (1 + R2 ÷ R1)

  = 2 × (1 + 4,000 ÷ 1,000)

  = 2 × 5

  = +10 V

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