That provides a controlled ahead bias existing, a reverse bias voltage, as well as the activating interface between the Regulate signal—typically a electronic logic command and one or more PIN diodes. This driver function is usually rendered to be a discrete structure, or with specialized ICs to suit the application. https://pin-diode-switch90009.blogrenanda.com/43925435/the-smart-trick-of-pin-diode-switch-that-nobody-is-discussing