The simplest MOS gate circuit is an inverter made using a single n-channel MOSFET switch with a pull-up device as shown in Figure 5.1. The pull-up device could be a resistor, as in Figure 5.1a, or an active device, as in Figure 5.1c. MOS inverter designs: (a) General MOS inverter using an n-channel MOSFET switch and a pull-up device, (b) MOS inverter using a pull-up resistor, and (c) MOS inverter using a depletion mode n-channel MOSFET as the pull-up device. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315275352/bf4c21b1-2787-4aee-842a-7426ebf51860/content/fig5_1.tif"/>