1. CHAPTER 5 FIELD EFFECT TRANSISTORS(part c) (FETs)

2. The MOSFETs MOSFET – Metal Oxide Semiconductor Field Effect Transistors 2 basic types of MOSFET : -Depletion – MOSFET - Enhancement – MOSFET (widely used) Different from JFET because they don’t have pn junction structure – instead, the gate is insulated from the channel by a silicon diode (SiO 2 ) layer.

3. Depletion – MOSFET (D-MOSFET) The drain and source are diffused into the substrate material. It connected by a narrow channel adjacent to the insulated gate. The operation for both junctions are same except the voltage polarities.

4. Depletion – MOSFET (D-MOSFET) D-MOSFET SymbolBasic structure of D-MOSFET

5. Depletion – MOSFET (D-MOSFET) Depletion mode The n-channel operates when a negative gate-to Source voltage is applied Enhancement mode The n-channel operates when a positive gate-to source voltage is applied It can be operated either in 2 modes :

6. Enhancement – MOSFET (E-MOSFET) E-MOSFET SymbolBasic structure of E-MOSFET

7. Enhancement – MOSFET (E-MOSFET) It can be operated enhancement mode only. It has no structural channel. Enhancement mode For n-channel, a positive V G above a threshold value induces a channel by creating a thin layer of negative charge V G <V G(th) = no channel

8. Characteristic and parameter n channel E-MOSFET Transfer Characteristic Curve p channel I D =K(V GS -V GS(th) ) 2

9. Characteristic and parameter D-MOSFET Transfer Characteristic Curve n channel

10. Examples 1. I D(on) =100mA at V GS =8V and V GS(th) =4V. Find I D when V GS =6V(E-MOSFET) 2. Determine I DSS, given I D =3mA, V GS =-2V and V GS(off) =-10V