**Different operating regions of CMOS inverter**

**Question: Describe the different operating regions of CMOS inverter with a neat sketch?**

**Solution**

**Region A: **This region occurs when **0≤V _{in}<V_{tn }**in which the n-device is cut-off(I

_{dsn}=0) and the p-device is in the linear region. Since I

_{dsn}=-I

_{dsp}, the drain-to-source current I

_{dsp }for the p-device is also zero. But for

**V**with V

_{dsp}=V_{out}-V_{DD}_{dsp}=0,

The output voltage in this region is: V_{out}=V_{DD}

**Region B: **This region occurs when **V _{tn}≤V_{in}<V_{DD}/2** in which the p-device is in the linear region and the n-device is in the

**saturation region**. The saturation current I

_{dsn }for the n-device is obtained by setting V

_{gs}=V

_{in}.

This\;results\;in\;\;I_{dsn}=\frac{\beta_n}2\lbrack\;V_{in}-V_{out}\rbrack^2

In region B, I_{dsp} is governed by voltages V_{gs} and V_{ds} described by:**V _{gs}=(V_{in}-V_{DD})** and

**V**

_{ds}=(V_{out}-V_{DD}).The output voltage in this region is : **V _{out}>V_{DD}/2**

**Region C: **This region occurs when **V _{in}=V_{DD}/2** in which both the p-device and the n-device are in the saturation region. The saturation currents for the two devices are obtain with I

_{dsp}=-I

_{dsn}.

\begin{array}{l}I_{dsp}=\frac{\beta_p}2\lbrack\;V_{in}-V_{DD}-V_{tp}\rbrack^2\\\\and\\\\I_{dsp}=\frac{\beta_n}2\lbrack\;V_{in}-V_{tn}\rbrack^2\\\end{array}

The output voltage **V _{DD }**drops sharply

**Region D: **This region occurs when **V _{DD}/2** <

**V**≤

_{in}**V**+

_{DD}**V**in which the n-device is in the linear region and the p-device is in the saturation region. The saturation currents for the two devices obtain with I

_{tp}_{dsp}=-I

_{dsn}.

\begin{array}{l}I_{dsp}=-\frac{\beta_p}2\lbrack\;V_{in}-V_{DD}-V_{tp}\rbrack^2\\\\and\\\\I_{dsp}=\beta_n\lbrack\;(V_{in}-V_{tn}{)V_{out}-\frac{V_{out}^2}2\rbrack}\\\end{array}

The output voltage in this region is : **V _{out}<V_{DD}/2**

**Region E: **This region occurs when **V _{in}≥V_{DD}-V_{tp} **in which the p-device is cut-off(I

_{dsp}=0) and the n-device is in the linear region.Here

**V**,Which is more positive than

_{gsp}=V_{in}-V_{DD}**V**

_{tp}The output voltage in this region is **V _{out}=o**

Different operating regions of CMOS inverter

**Read: Switching threshold of CMOS inverter**