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The saturation current (or scale current), more accurately the reverse saturation current, is the part of the reverse current in a semiconductor diode caused by diffusion of minority carriers from the neutral regions to the depletion region. This current is almost independent of the reverse voltage.
Like other MOSFETs, nMOS transistors have four modes of operation: cut-off (or subthreshold), triode, saturation (sometimes called active), and velocity saturation. NMOS AND-by-default logic can produce unusual glitches or buggy behavior in NMOS components, such as the 6502 "illegal opcodes" which are absent in CMOS 6502s.
MOSFET drain current vs. drain-to-source voltage for several values of ; the boundary between linear (Ohmic) and saturation (active) modes is indicated by the upward curving parabola. Cross section of a MOSFET operating in the linear (Ohmic) region; strong inversion region present even near drain.
Enhancement-mode MOSFETs (metal–oxide–semiconductor FETs) are the common switching elements in most integrated circuits. These devices are off at zero gate–source voltage. NMOS can be turned on by pulling the gate voltage higher than the source voltage, PMOS can be turned on by pulling the gate voltage lower than the source voltage.
A resistor (with the current simply proportional to the voltage) would be better, and a current source (with the current fixed, independent of voltage) better yet. A depletion-mode device with gate tied to the opposite supply rail is a much better load than an enhancement-mode device, acting somewhere between a resistor and a current source.
Extremely little current flows below this voltage. The threshold voltage , commonly abbreviated as V th or V GS(th) , of a field-effect transistor (FET) is the minimum gate-to-source voltage (V GS ) that is needed to create a conducting path between the source and drain terminals.
The 2N7000 has been referred to as a "FETlington" and as an "absolutely ideal hacker part." [3] The word "FETlington" is a reference to the Darlington-transistor-like saturation characteristic.
The charge gradient is increased across the base, and consequently, the current of minority carriers injected across the collector-base junction increases, which net current is called . Both these factors increase the collector or "output" current of the transistor with an increase in the collector voltage, but only the second is called Early ...