emittor

Emittor, or emitter in English, is a term used for a source that sends out something—electrons, photons, or signals. The standard English spelling is emitter; emittor is a less common variant and appears in some texts or translations. In electronics, the concept is most often encountered as the emitter terminal of a bipolar junction transistor (BJT). In other contexts, it can refer to any component or region that emits energy or particles.

In a BJT, the emitter is the heavily doped region that injects charge carriers into the base. The emitter-base junction is forward biased during normal operation, and the transistor amplifies by controlling the flow of carriers from emitter to collector. The total emitter current I_E equals the sum of base current I_B and collector current I_C (I_E = I_B + I_C). In circuit practice, common-emitter and emitter-follower configurations are common; in a common-emitter amplifier, the output is taken from the collector; in an emitter-follower, the emitter follows the base voltage with a small drop.

In optoelectronics, the emitter can refer to the light-emitting region in devices such as LEDs and laser diodes, where electron-hole recombination generates photons. The term is sometimes used interchangeably with the active region, though more precise terminology distinguishes electrical injection regions from optical emission regions.

Other uses of the term include any particle or radiation source designated as an emitter, such as a neutron emitter or a chemical emitter in radiative or acoustic contexts. In schematic symbols, the emitter terminal is labeled E, and for a bipolar transistor the symbol includes an arrow on the emitter indicating the direction of forward current: outward for NPN and inward for PNP devices.