Inverting Amplifiers

An inverting amplifier is shown in figure 6.4. Analysis of the circuit gives

 
Figure 6.4:  Inverting amplifier.

Since ( is at virtual ground),

The gain is

The output is inverted with respect to the input signal.

A sketch of the frequency response of the inverting and non-inverting amplifiers are shown in figure 6.5.

 
Figure 6.5:  Inverting and non-inverting amplifier frequency response.

The input impedance of the inverting amplifier is . Since we have .

A better circuit for approximating an ideal inverting amplifier is shown in figure 6.6

 
Figure 6.6:  Inverting amplifier with bias compensation.

The extra resistor is a current bias-compensation resistor. It reduces the current bias by eliminating non-zero current at the inputs.