Device geometry

Device geometry determination

After finding the minimum drain voltage and current, the geometry of the device needs to be investigated. To start off, a lenght of $L=180nm$ is suggested as this is the minimal length of the transistor. Now, in order to select the width (or the multiplication factor M), the output characteristics for varying M with $W=50\mu m$ can be plotted:

From these result the effect of increasing the width of the transistor becomes visible. Increasing the width will increase the current through the transistor and thus the transconductance gm will also increase. From the obtained figure we can see that for low values such as $M=1$ the circuit is not able to achieve the desired output voltage driving capabilities. For $M>12$ we obtain $V_{out}\ge 620mV$. Which seems to be sufficient for the design.