LectureNotes_7 - The p-channel MOSFET A p-channel...

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The p- channel MOSFET A p- channel enhancement-type MOSFET (PMOS transistor) fabricated on an n - type substrate with p+ regions for the drain and the source, has holes as charge carriers. The device operates in the same manner as the n -channel device except that V GS , V t and V DS are all negative. Also the current I D enters the source terminal and leaves through the drain terminal. PMOS technology originally dominated MOS manufacturing. However because NMOS devices can be made smaller and thus operate faster and also because NMOS required lower supply voltages than PMOS, NMOS technology has virtually replaced PMOS. Nevertheless, it is important to be familiar with the PMOS transistor for two reasons: PMOS devices are still available for discrete-circuit design and more importantly , both PMOS and NMOS transistors are utilized in complementary MOS or CMOS circuits the dominant MOS technology. Complementary MOS or CMOS CMOS technology employs MOS transistors of both polarities. Although CMOS circuits are somewhat more difficult to fabricate than NMOS, the availability of complementary devices makes possible many powerful circuit- design possibilities. CMOS is the most widely used of all the IC technologies in both analogue and digital circuits. CMOS technology has taken over many applications that hitherto were only possible with bipolar devices.
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In fabricating the NMOS transistor is implemented directly in the p- type substrate, while the PMOS transistor is fabricated in a specially created n region, known as an n well. The two devices are isolated from each other by a thick region of oxide that functions as an insulator. Circuit Symbol B S G D S G B D n -channel enhancement- type MOSFET p -channel enhancement- type MOSFET Observe that the spacing between the two vertical lines that represent the gate and the channel indicates that the gate electrode is insulated from the body of the device. For the n-channel device the polarity
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This note was uploaded on 02/23/2011 for the course ELETRONICS P24L taught by Professor Learymyers during the Spring '11 term at University of the West Indies at Mona.

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LectureNotes_7 - The p-channel MOSFET A p-channel...

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