Inverting Amplifier

An inverting amplifier increases the amplitude of a signal. But due to the fact that the signal is fed into the inverting input, the output signal will be inverted. However, unlike Non-inverting amplifiers, they can have a gain of less than one.

One thing to note quickly. The output can never be higher than the positive supply voltage, or lower than the negative supply voltage. This means that for an inverting amplifier to work you need the negative supply pin to have a voltage below ground (e.g -6v).

Inverting amplifier

In inverting amplifiers, the gain can be calculated by dividing Vout by Vin. In addition to this, the same figure can also be acquired by dividing the feedback resistance by the input resistance ( feedback resistance = Rf, Input resistance = R1) . However, because the output is inverted, the value of the feedback resistance needs to be inverted too. From all of this, we can deduce the following equations:

Gain=VoutVinGain=-RfR1

If two inverting amplifiers are used in series, the inversion can be rectified. A schematic and equation is shown below to demonstrate this.

Inverting amplifiers in series

The gain of the first op amp is calculated:

IA1

 

 

Then the gain of the second op amp:

IA2

Now assuming that Vin = 0.5v, the output of the first op amp would be the following:
IA3

Finally, with -5v being inputted into the second op amp, the output will be once again positive:

IA4

Therefore the total gain of the circuit is 10, meaning that the inversion has been rectified.

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