No actual current flows until V_in crosses V_tn , as may be seen from Figure 2.11. The operating point of the p -transistor moves from higher to lower values of currents in linear zone. The output voltage is given by , as may be seen from Figure 2.12.

Region 2 : the input voltage is in the range . The upper limit of V_in is V_inv , the logic threshold voltage of the inverter. The logic threshold voltage or the switching point voltage of an inverter denotes the boundary of "logic 1" and "logic 0". It is the output voltage at which V_in = V_out . In this region, the n-transistor moves into saturation, while the p-transistor remains in linear region. The total current through the inverter increases, and the output voltage tends to drop fast.

Figure 2.12 Transfer characteristics of the CMOS inverter