Important observations can be made between the inverting and non-inverting application circuits. In the non-inverting configuration V_in , V_n, and V_os are all applied to the non-inverting terminal and the signal gain is equal to the noise gain. In the inverting configuration the signal is applied to the inverting terminal while V_n and V_os are applied to the non-inverting terminal. The signal gain is not equal to the noise gain in the inverting configuration. With the assigned resistor values in Table 3-2 and Table 3-2 the THD + N gain differs by a factor of $2 \frac{V}{V}$ or 6 dB between the inverting and non-inverting configurations. The difference of 6 dB between these two measurements is shown in Figure 3-12. The output referred THD + N measurement is always worse for the inverting configuration when configured in the same signal gain as the non-inverting configuration. Although the THD + N is worse, the benefit of the inverting configuration is that non-inverting terminal is fixed to a DC potential as seen in Figure 3-8 and provides a fixed common mode voltage. This results in a CMRR benefit for the inverting configuration when the op amp has low CMRR.

Figure 3-12 THD + N (dB) Inverting and Non-Inverting