So it has high efficiency than other devices. MOSFET generates very less heat loss compared to BJT at high currents. It also has applications in low power high-frequency converters.Īdvantages of using MOSFET instead of BJT is it does not have the problem of second breakdown phenomena as in BJT.
The switching speed of MOSFET is very high and it has switching time in order of nanoseconds. This MOSFET is used for high-speed switching operations. A power MOSFET is a voltage controlled device. Here gate is isolated from the channel by metal oxide thin layer. It has mainly three terminal – Gate ( G), Drain ( D) and source ( S ). As a voltage-controlled current source, a MOS transistor can be characterized by its transconductance: Ĭompare NMOS Equation to PMOS Equation (Cut-off) (triode) (saturation) Valid for NMOS (saturation) (triode) (Cut-off) Valid for PMOSMosfet is a metal oxide semiconductor device.The slope of the electron profile increases. The effective base width (WB) is reduced. Similarity to Early Effect A larger reverse bias voltage leads to a larger BC depletion region. Pronounced Channel Length Modulation in small L Limited VDS Dependence In Saturation As VDS increase, effective L decreases, therefore, ID increases. PMOS in Saturation Region - ++++++++ P+ P+ N+ N P Substrate= 0V Induced holesĭetermine Region of Operation (6.40) Assume that VTHN=0.4 V and VTHP=-0.4 V PMOS in Triode Region - +++++++++ P+ P+ N+ N P Substrate= 0V Induced holes PMOS: Formation of Channel - ++++++++++ P+ P+ N+ N P Substrate= 0V Induced holes PMOS in Cut-Off Mode - P+ P+ N+ N P Substrate= 0V Regions (No Dependence on VDS) No channel Assumption:ĭetermine Region of Operation (6.19) Tricky! Assume that VTHN=0.4 V and VTHP=-0.4 V Drain can no longer affect the drain current! VG-VD is sufficiently large to produce a channel VG-VD is NOT sufficiently large to produce a channel No channel Electrons are swept by E to drain. Positive charges repel the holes creating a depletion region, a region free of holes.
VTH=300mV to 500 mV (OFF) (ON) Free electrons appear at VG=VTH. tox is made really thin to increase C, therefore, create a strong control of Q by V.Ī Closer Look at the Channel Formulation Need to tie substrate to GND to avoid current through PN diode. Typical Dimensions of MOSFETs These diode must be reversed biased. A conductive path is created If the density of electrons is sufficiently high. Positive charge attract negative charges to the interface between insulator and silicon. V1 can control the resistivity of the channel.
Introduction to MOS Transistors Section 6.1-6.4 Selected Figures in Chapter 15
0 kommentar(er)
