Difference Between Inverting and Noninverting Amplifier

The main difference between inverting and noninverting amplifier is that an inverting amplifier produces an output that is 180^o out of phase with the input, whereas a noninverting amplifier produces an output that is in phase with the input.

Operational amplifiers can be arranged in two fundamental configurations: inverting and noninverting amplifiers. An inverting amplifier is a differential amplifier that amplifies a small difference in voltage between its input terminals to a large voltage on its output terminal. On the other hand, a noninverting amplifier is an amplifier that produces an output that is in phase with the input.

Key Areas Covered

1. What is an Inverting Amplifier
      – Definition, Features
2. What is a Noninverting Amplifier
      – Definition, Features
3. Difference Between Inverting and Noninverting Amplifier
      – Comparison of Key Differences

Key Terms

Inverting Amplifier, Noninverting Amplifier, Operational Amplifiers

What is an Inverting Amplifier

An inverting amplifier is a differential amplifier that amplifies a small difference in voltage between its input terminals to a large voltage on its output terminal. The output voltage is at 180^o out of phase compared to the input voltage. The setup of an inverting amplifier is shown below.

Difference Between Inverting and Noninverting Amplifier - Inverting_Amplifier

Figure 1: An Operational Amplifier

For amplifiers, the output voltage $V_{out}$ is given in terms of the two input voltages $V^+$ and $V_-$ as:

$V_{out}=A\left( V_+-V_-\right)$

where $A$ is the gain of the operational amplifier. Since $V_+$ is connected to Earth, $V_+=0$ . The point marked $X$ is virtual Earth so the potential at this point is almost 0 V. No current passes through this point. Therefore the current that flows through the resistor $R_2$ is the same as the current $I$ that flows through the resistor $R_1$ .

If the potential difference across $R_1$ is $V_1$ , then,

$I=\frac{V_1}{R_1}=\frac{V_{in}-0}{R_1}=\frac{V_{in}}{R_1}$

Similarly for $R_2$ ,

$I=\frac{V_2}{R_2}=\frac{0-V_{out}}{R_2}=-\frac{V_{out}}{R_2}$

Then the gain $A$ can be expressed as:

$A=\frac{V_{out}}{V_{in}}=\frac{-IR_2}{IR_1}$

$A=-\frac{R_2}{R_1}$

The negative sign here indicates that the output is at a 180^o phase difference with the input.

What is a Noninverting Amplifier

A noninverting amplifier is an amplifier that produces an output that is in phase with the input. The setup of a non-inverting amplifier is shown below:

Difference Between Inverting and Noninverting Amplifier - Noninverting_Amplifier

Figure 2: A Noninverting Amplifier

In the noninverting amplifier, $V_{in}=V_+$ . The gain in a noninverting amplifier is quite large, so the difference between $V_+$ and $V_-$ is negligible. So we can say that $V_-\approx V_+ \left( =V_{in}\right)$ . Using the idea of a potential divider, we can write

$V_-=V_{out}\times \frac{R_2}{R_1+R_2}$ . Equating the two expressions for $V_-$ , we have:

$V_{in}=V_{out}\times \frac{R_2}{R_1+R_2}$ . Then, we can write the gain as:

$A=\frac{V_{out}}{V_{in}}=\frac{R_1+R_2}{R_2}$ . Dividing both the numerator and the denominator by $R_2$ , we get:

$A=1+\frac{R_1}{R_2}$

Difference Between Inverting and Noninverting Amplifiers

Definition

An inverting amplifier is a differential amplifier that amplifies a small difference in voltage between its input terminals to a large voltage on its output terminal. On the other hand, a noninverting amplifier is an amplifier that produces an output that is in phase with the input.

Phase Difference

In an inverting amplifier, the output voltage is 180^o out of phase with the input voltage, but in a noninverting amplifier, the output voltage is in phase with the input voltage.

Amplifier Gain

For an inverting amplifier, the gain is simply the ratio between the two resistors, while for a noninverting amplifier, the gain is 1 + the ratio between resistors.

Conclusion

Operational amplifiers can be arranged in two fundamental configurations: inverting and noninverting amplifiers. The main difference between inverting and noninverting amplifier is that an inverting amplifier produces an output that is 180o out of phase with the input, whereas a noninverting amplifier produces an output that is in phase with the input.