CHAPTER 8: MOSFETS.OBJECTIVES docx

CHAPTER 8 MOSFETS OBJECTIVES Describe and Analyze: • Theory of MOSFETS • MOSFET Amplifiers • E-MOSFET Switches • Troubleshooting Introduction • MOSFET stand for Metal-Oxide-Semiconductor (or Metal-Oxide-Silicon) Field-Effect-Transistor • Like JFETs, MOSFETs come in N-channel and P-Channel types • Unlike JFETs, MOSFETs can be manufactured as enhancement-mode (E-MOSFETs) as well as depletion-mode (D-MOSFETs). • There is no PN junction. The metal gate of a MOSFET is isolated from the silicon channel by a thin layer of silicon oxide (Si O2, commonly known as glass) • MOSFETs can be damaged by static electricity D-MOSFETs Similar to a JFET, but Zin of device is almost infinite D-MOSFETs Unlike JFETs, D-MOSFETS can work with zero bias D-MOSFETs The same bias circuits used with JFETs can be used with E-MOSFETs. In addition, a class-A MOSFET amplifier can work with VGS = 0. D-MOSFET Amplifiers The equations for Zin, Zout and Av developed for JFET amplifiers can be used with D-MOSFET amplifiers. Like JFETs, D-MOSFETs are used in the front ends of radio receivers because of their inherently low internal noise. D-MOSFET AGC Amplifiers Since gm depends on the Q-point, MOSFETs are used for Automatic Gain Control in radio receivers D-MOSFET Mixers Unlike JFETs, D-MOSFETs can be built with two gates. That allows them to be used as radio “mixers” to multiply one signal by another. E-MOSFETs In an enhancement-mode MOSFET, the drain is isolated from the source because the substrate is doped opposite the source and drain. Voltage applied to the gate causes the substrate under the gate to “flip polarity”. P-material becomes N-material as charge carriers are attracted into the region by the gate. . CHAPTER 8 MOSFETS OBJECTIVES Describe and Analyze: • Theory of MOSFETS • MOSFET Amplifiers • E-MOSFET Switches • Troubleshooting. Field-Effect-Transistor • Like JFETs, MOSFETs come in N-channel and P-Channel types • Unlike JFETs, MOSFETs can be manufactured as enhancement-mode (E -MOSFETs) as well as depletion-mode (D -MOSFETs) . • There. glass) • MOSFETs can be damaged by static electricity D -MOSFETs Similar to a JFET, but Zin of device is almost infinite D -MOSFETs Unlike JFETs, D-MOSFETS