Four types of MOSFETs
Time:2024-01-20
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The channel, i.e. MOS transistor, is an enhanced type. The arrow on substrate B points towards the interior of the MOS transistor, indicating that the conductive channel is N-type. The gate lead out end is drawn on the side near the source electrode.
2. P-channel enhanced type
The symbol of P-channel enhanced MOSFET is shown in Figure 3.3.6, where the arrow pointing outward on the substrate indicates that the conductive channel is P-type.
When v=0, the MOSFET is not conducting and the output is at a low level. VoL. As long as R is much smaller than the cutoff internal resistance of the MOS transistor RorF, then. VoL=VvD.
When v1
1. N-channel depletion type
The structural form of N-channel depleted MOSFETs is the same as that of N-channel enhanced MOSFETs, both using P-type substrates and N-type conductive channels. The difference is that in the depletion of VpD type MOSFETs, a certain concentration of positive ions is doped into the silicon dioxide insulation layer below the gate. The electric field formed by these positive ions is sufficient to attract a few charge carriers - electrons - from the substrate to the substrate surface below the gate, forming conductive channels between D-S. Due to this, conductive channels already exist when vCS=0. VC3 increases; When it is negative, the conductive channel v becomes wider when it is positive, and i vGS becomes narrower and i decreases.
Until v is less than a certain negative voltage value VcS (eff), the conductive channel disappears and the MOS transistor cuts off. Figure 3.3.8 of V6S (eff) shows the pinch off voltage of an N-channel depletion MOSFET with P-channel enhancement. The switch circuit diagram 3.3.9 of MOS transistor connection is the symbol of N-channel depletion type MOS transistor. In the diagram, D-S is connected, indicating the presence of conductive channels when vCS=0. The rest of the drawing is the same as the enhanced MOSFET. During normal operation, the substrate of N-channel depleted MOSFETs should also be connected to the potential of the source or system.
2. P-channel depletion type
The structure of P-channel depletion type MOSFETs is the same as that of P-channel enhancement type MOSFETs, and they are also N-type substrates with P-type conductive channels. The difference is that in P-channel depletion type MOSFETs, when vcs=0, conductive channels already exist in vCs. When the VCS is negative, the conductive channel is further widened and the value of i increases; When vCS is positive, the conductive channel narrows and i decreases. When the positive voltage of (v) is greater than the clamping voltage Vcs (odf), the conductive channel disappears and the tube cuts off.
Figure 3.3.10 is the symbol of a P-channel depletion MOSFET. When working, its substrate should be connected to the source electrode, or the substrate should be connected to the potential of the system.
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