A MOSFET(Metal Oxide Semiconductor Field Effect Transistor) is a three terminal semiconductor transistor. There are two types of MOSFET- depletion MOSFET(or D-MOSFET) and enhancement-MOSFET(E-MOSFET). Each of the two types is further divided by N-type and P-type, that is N-channel depletion MOSFET and P-channel depletion MOSEFT, N-channel enhancement MOSFET and P-channel enhancement MOSEFT. The N-channel and P-channel MOSFETs differs in what type of material is used as substrate. If the substrate is N-type then an N-Channel MOSFET results and if the substate is P-Type then we have P-Channel MOSFET. Here we will explain the different between Depletion MOSFET and Enhancement MOSFET.
Depletion MOSFET | Enhancement MOSFET |
---|---|
There is N-Channel | There is NO N-Channel |
Can be operated on both negative and positive gate voltage | Can be operated with only positive gate voltage |
Normally ON, when gate voltage is zero | Normally OFF, when gate voltage is zero |
Drain current is flowing whether gate to souce voltage(\(V_{GS}\)) is positive or negative | Drain current starts flowing when the gate to souce voltage(\(V_{GS}\)) is greater than the threshold voltage(\(V_{th}\)) is reached |
Transfer curve is defined by Shockley’s equation | Transfer curve is NOT defined by Shockley’s equation |
Drain Current: \(I_D = I_{DSS}(1-\frac{V_{GS}}{V_{GS(off)}})^2\) |
Drain Current: \(I_D = k(V_{GS}-V_{th})^2\) where,\(k=\frac{I_{D(on)}}{(V_{GS(on)}-V_{th})^2}\) |
Biasing Methods: (1) Zero Gate Bias Depletion MOSFET (2) Fixed Gate Bias Depletion MOSFET (3) Self Bias Depletion MOSFET (4) Voltage Divider Bias Depletion MOSFET (5) Current-source bias Depletion MOSFET |
Biasing Methods: (1) Ohmic Region Biasing (2) Fixed Gate Bias Enhancement MOSFET (3) Drain Feedback Bias Enhancement MOSFET (4) Voltage Divider Bias Enhancement MOSFET |
N-channel D-MOSFET drain curve |
E-channel D-MOSFET drain curve |
N-channel D-MOSFET transfer curve |
N-channel E-MOSFET transfer curve |
N-channel D-MOSFET symbol |
N-channel E-MOSFET symbol |
Applications - Used as RF amplifiers in high-frequency front-end communications circuits |
Applications - Used mainly as switches in both discrete and integrated circuits. In discrete circuits, it is mainly used as power switches and in integrated circuits it is used fir digital switching - sometimes used in Class-AB power amplifier - also used as front-end high-frequency RF amplifiers |