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.