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July 20, 2019
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Op Amp Inverting Amplifier: Operational Amplifier Circuit

Op Amps

The op amp inverting amplifier circuit is very easy to design and can be implemented with a very limited number of additional components.

In its simplest form the op amp inverting amplifier only requires the use of two additional resistors.

This the inverting amplifier can also be used as a virtual earth mixer, but it is also worth noting that the input impedance of this op amp circuit is not as high as the inverting format.

Op amp inverting amplifier circuit

The basic diagram for the inverting Op Amps circuit is quite straightforward and only needs a few components beyond the operational amplifier integrated circuit itself.

The circuit consists of a resistor from the input terminal to the inverting input of the circuit, and another resistor connected from the output to the inverting input of the op-amp. The non inverting input is connected to ground.

Inverting amplifier gain

One of the main features of the inverting amplifier circuit is the overall gain that it produces. This is quite easy to calculate. The voltage gain, Av, is actually the output voltage (Vout) divided by the input voltage (Vin), i.e. it is the number of times the output voltage is larger than the input voltage.

It is also easy to determine the equation for the voltage gain. As the input to the op-amp draws no current this means that the current flowing in the resistors R1 and R2 is the same.

Op amp inverting amplifier design hints and tips

The op amp inverting amplifier is very easy to design, but as with any design there are a few hints and tips that can be of use.

  • Don’t make R2 too high:   Although the input impedance of op amps is high, it is always best to ensure that the value of R2 is not chosen to be too high otherwise other circuit effects may load it and the value of gain may not be what is expected. It is often wise to keep the value of R2 below 100kΩ as a rough rule of thumb.
  • Don’t make R1 too low:   It is also wise not to make the value of R1 too low in the op amp inverting amplifier. Remember that it determines the input resistance of the inverting amplifier circuit. If AC coupling the input circuit, the value of the series coupling capacitor will need to be chosen so that its reactance is sufficiently low at the lowest frequencies needed. Lowering the value of R1 increases the value of capacitor required. Also making R1 too low increases the loading on the previous stage.
  • Remember bandwidth:   Although Op Amps have a high value of gain, this starts to fall at increasing frequencies. Even with feedback in the inverting amplifier, the gain bandwidth product needs to be considered. Don’t try to get too much gain out of a single stage, otherwise the frequency response may suffer.

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