MOSFETs have three regions of operation: cutoff, saturated, and resistive. The MOSFET also has three terminals, the gate G, the drain D, and the source S. A key parameter characterizing the MOSFET is a threshold voltage Vth. When the G-S voltage is below the threshold voltage, no drain current flows and the transistor is cut off.
Because most signals in the real world are analog but digital computers work on discretizations, it is necessary to convert between digital and analog signals. As mentioned above, this is done through digital-to-analog and analog-to-digital converters. Most approaches to digital-to-analog conversion use summers, where the voltages representing the digital bits are applied to input resistors, either directly or indirectly through switches gated on by the digital bits which change the input resistance fed by a dc source.
The operation that results is a linear combination of incoming signals to generate the output signal. The sign appearing alongside each input to the summing point indicates the sign of that signal as it appears in the output.
A general term referring to a system or part of a system of conducting parts and their interconnections through which an electric current is intended to flow. A circuit is made up of active and passive elements or parts and their interconnecting conducting paths.