In the saturation or linear region, the transistor will be biased so that the maximum amount of gate voltage is applied to the device which results in the channel resistance R DS.įor the different values of input voltages, the operating regions are listed below for both transistors In Linearregion the relation between V DS and I D is almost ohmic. In this region, the transistor will be off or its act as an open circuit. In the cut-off region, the transistor acts as an open-circuit between drain and source, in the linearregion the relation between V DS and I D is almost ohmic, and in the saturation mode, the current is – ideally – independent on V DS. Each region has its own conditions, properties, and equations, as described in the following Table In the case of a MOSFET, The relationship between the drain current (I D) and the gate-to-source voltage (V GS) is highly non-linear, and it is divided in three operating regions. In electronic terms, the working principle of a transistor is very simple, it has three main terminals, Gate, Drain & Source. This is why NMOS require positive voltages (to attract electrons) and PMOS require negative voltages (to attract holes) for channel formation. When enough charge is accumulated in that region, the minority carriers become the majority carriers, forming a channel with the same type as the drain and source. The gate is connected to a thin layer of silicon dioxide, that insulates the gate connection from the substrate. The drain and source regions are strongly doped with N-dopants (NMOS) or P-dopants (PMOS), and the substrate is doped with the opposite type (P-type for NMOS and N-type for PMOS). This process uses semiconductor doping and oxide growth to create N-type, P-type and insulating regions. MOS transistors are built on top of silicon wafers. NMOS transistors provide a smaller footprint than PMOS for the same output current.The ON resistance of an NMOS is almost half of a PMOS.Secondly, the charge carriers are not the same: NMOS uses electrons and PMOS uses holes as majority carriers. The polarity of the voltage: the threshold voltage V TH, the V GS, and the V DS are negative. NMOS uses N-type doped semiconductors as the source and drains and P-type as the substrate, whereas the PMOS is the opposite. There are two types of MOSFETs: the NMOS and the PMOS. 1.1.3 Saturation region NMOS and PMOS Models
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