Op-amp AC voltage amplifier

The operational amplifier can be successfully used as an AC voltage amplifier using an unipolar power supply (Fig. 1).

Fig. 1. Op-amp AC voltage amplifier

This is achieved by:

1. connecting decoupling capacitors (C₁ and C₃) at the input and output;
2. forming a virtual ground of the operational amplifier (R₁ and R₂).

The presence of this virtual ground is associated with the need to amplify both half-waves of the input signal. It is advisable to select R₁ and R₂ so as to set (in the absence of an input signal) a voltage at the op-amp output equal to half the supply voltage.

An important element of the op-amp amplifier circuit with an unipolar power supply is the decoupling capacitor C₂, which eliminates the constant component of signals in the feedback circuit. Thus, the gain of the amplifier for direct current is equal to one. The presence of the negative feedback for direct current in the amplifier allows you to get rid of various drifts when the supply voltage (within small limits) and temperature change.

In this case, the C₂R₃ circuit is a high-pass filter. Its parameters determine the lower limit of the frequency range of the AC amplifier.