User:John R. Brews/Sample

In electronics, the mode of an electrical device refers to its steady-state bias condition or operating point in the absence of signals. In analog circuits the so-called active mode of the device is chosen by the circuit designer to allow adequate signal amplitude and adequate voltage or current gain, along with acceptable signal distortion. In digital circuits, devices toggle between modes that are either in cutoff mode (off) or in ohmic mode (on), and visit the active mode only briefly during the transition between the on and off modes.

For historical reasons, some confusing nomenclature has arisen that is only slowly being replaced. For both bipolar and MOSFET devices, it is common to refer to the off mode as cutoff. However, the active mode of the bipolar transistor often is called the saturation mode of the MOSFET, while the on mode of the bipolar transistor often is called its saturation mode. This confusion of terminology does nothing to clarify the discussion of circuitry.

MOS transistor	G-S Bias	G-D Bias	S-B Bias	D-B Bias	Mode
Channel at source end only	≥ VT(S)	≤ VT(D)	Zero or Reverse	More reverse than S-B	Active (Saturation)
Channel at both ends	≥ VT(S)	> VT(D)	Zero or Reverse	More reverse than S-B	Ohmic
No channel	< VT(S)	≤ VT(D)	Zero or Reverse	Zero or reverse	Cutoff (Subthreshold)
Channel at drain end only	< VT(S)	≥ VT(D)	More reverse than D-B	Zero or Reverse	Reverse-active

Bipolar transistor	B-E Junction Bias	B-C Junction Bias	Mode
E injects, C collects	Forward	Reverse	Forward active
E and C inject	Forward	Forward	Saturation
No injection	Reverse	Reverse	Cut-off
C injects, E collects	Reverse	Forward	Reverse-active