Supplementary Reader IV EECS 40 Introduction to Microelectronic Circuits Prof. C. Chang-Hasnain Fall 2006EE 40, University of California Berkeley Professor Chang-Hasnain i Table of Contents Chapter 4. Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET).......................................... 1 4.1 Introduction ................................................................................................................................. 1 4.2 Notation....................................................................................................................................... 1 4.3 NMOS and PMOS Transistors .................................................................................................... 2 4.4 N-MOSFET Operating Regions .................................................................................................. 2 4.4.1 Cut-off .................................................................................................................................... 2 4.4.2 Triode ..................................................................................................................................... 3 4.4.3 Saturation................................................................................................................................ 3 4.5 PMOSFET Operating Regions .................................................................................................... 4 Chapter 5. Simple MOSFET Circuits....................................................................................................... 5 5.1 Analysis for MOSFET Amplifiers .............................................................................................. 5 5.1.1 DC Analysis – Load-Line Analysis ........................................................................................ 5 5.1.2 Small-Signal Equivalent Circuit ............................................................................................. 5 5.1.3 Finding Voltage Gains, Input, and Output Resistances .......................................................... 6 5.2 The Inverter: ................................................................................................................................ 6 5.2.1 Constructing a Logic Gate: the Use of Pull-Down and Pull-Up Networks ............................ 7 5.2.2 NMOS Resistor Pull-Up ......................................................................................................... 7 5.2.3 The CMOS Inverter ................................................................................................................ 8 5.3 2-Input NAND Gate: ................................................................................................................. 10 5.4 2-Input NOR Gate ..................................................................................................................... 10EE 40, University of California Berkeley Prof.Chang-Hasnain 1 Chapter 4. Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) 4.1 Introduction A transistor is a semiconductor device that uses a small amount of voltage or electrical current to control a larger change in voltage or current. Because of its fast response and accuracy, it may be used in a wide variety of applications, including amplification, switching, signal modulation, and as an oscillator. The transistor is the fundamental building block of both digital and analog circuits — the circuitry that governs the operation of computers, cellular phones, and all other modern electronics. The field-effect transistor (FET) is a transistor that relies on an electric field to control the shape and hence the conductivity of a 'channel' in a semiconductor material. FETs are sometimes used as voltage-controlled resistors. Field-effect transistors are devices that are used in amplifiers and logic gates. The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), is by far the most common field-effect transistor in both digital and analog circuits. A MOSFET is a three-terminal device that uses the voltage between two terminals to control the current flowing in the third terminal. Therefore it can be realized as a voltage-controlled current source. Some of the basic symbols can be found in the following table. 4.2 Notation Superposition is a very important concept while analyzing transistors. For this reason, many types of variables with different subscripts are used. Upper-case letters with upper-case subscripts, e.g. VGS, represent results due to DC analysis. For the value of a single point, it is usually labeled with a subscript “Q”, e.g. VGSQ. Lower-case letters with lower-case subscripts, e.g. vgs, represent results due to AC analysis. Finally, lower-case letters with upper-case subscripts, e.g. vGS, represent the general or total, i.e. the result achieved by summing the DC and the AC results. Symbol Definition N-MOSFET symbols. Note that the Drain terminal is on top and the Source terminal on bottom. In the first picture, the arrow points towards the Gate terminal. P-MOSFET symbols. Note that the Source terminal is on top and the Drain terminal on bottom. In the first picture, the arrow points away from the Gate terminal. Table 1. Symbol Information depicting the symbols that will be used throughout the remainder of this text. Fig. 1. A device drawing of an NMOS transistor. L represents the length of the channel and W, the width.EE 40, University of California Berkeley Professor Chang-Hasnain 2 4.3 NMOS and PMOS Transistors Figure 1 depicts the structure of an n-channel enhancement-mode MOSFET, also known as an NMOS transistor. The substrate, or body, is doped with acceptors to form p-type silicon. Two regions on the top surface of the substrate are doped to form n-type silicon as indicated by the n+ regions in the figure. Metal is deposited to form contacts to the n+ regions. The two contacts are labeled source (S) and drain (D), with another metal to contact the bottom of the substrate, labeled body (B). Between the source and drain, a metal contact is deposited on top of a layer of silicon dioxide, which, in turn, is deposited on top of the p-Si.
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