What is triode region in mosfet?
it is an operating regime where the drain current is controlled by three terminals instead of two as in the saturation regime. hence the name triode.
next to the door of a source, the drain also has an effect because the channel is always uninterrupted between the source and the drain. the drain current depends linearly on the drain-source voltage as a manifestation of the ohm’s law due to the uninterrupted channel. (By the way, this operating regime in a bipolar transistor is called saturation, which confuses a lot.)
Once the channel is pinched on the drain side, the excess drain voltage will drop in the depletion region and stop contributing. to the increase of the current. the saturated drain current / voltage curve, therefore the saturation region.
there is of course a second-order effect that makes his picture more complicated, but that’s another question.
The amount of current passing through a mosfet will depend on the voltage on the gate and the drain. a given gate voltage, at low drain-source voltages, the drain-source current will be approximately proportional to the drain-source voltage (triode mode). at higher drain-source voltages, the current will be essentially constant (saturation mode). at intermediate tensions, the behavior will be somewhere between these two modes.
amplifiers often use saturation mode transistors because, since there is a wide range of drain voltages, the identifiers are essentially independent of vds. on the other hand, there is a relatively narrow range of drain voltages where ids are reasonably proportional to vds. moreover, it is easier to design circuit elements capable of behaving in a reasonably linear manner with the independent identifiers of the virtual disks, than with identifiers proportional to virtual disks. designers of vacuum tube amplifiers may have preferred to use their amplification elements so that the anode current is independent of the anode voltage, but the vacuum tubes do not work that way . the triodes were used in triode mode because they were triodes.
As with digital circuits, the normal goal is to light the mosfets as hard as possible. If the amount of direct current flowing through a MOSFET is large enough to saturate it, it is generally a sign that the MOSFET must be larger or the amount of current absorbed through it must be smaller.