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Über dieses Buch

Circuit simulation is widely used for the design of circuits, both discrete and integrated. Device modeling is an impor­ tant aspect of circuit simulation since it is the link between the physical device and the sim ulate d device. Curren tly available circuit simulation programs provide a variety of built-in models. Many circuit designers use these built-in models whereas some incorporate new models in the circuit sim ulation programs. Understanding device modeling with particular emphasis on circuit simulation will be helpful in utilizing the built-in models more efficiently as well as in implementing new models. SPICE is used as a vehicle since it is the most widely used circuit sim ulation program. How­ ever, some issues are addressed which are not directly appli­ cable to SPICE but are applicable to circuit simulation in general. These discussions are useful for modifying SPICE and for understanding other simulation programs. The gen­ eric version 2G. 6 is used as a reference for SPICE, although numerous different versions exist with different modifications. This book describes field effect transistor models commonly used in a variety of circuit sim ulation pro­ grams. Understanding of the basic device physics and some familiarity with device modeling is assumed. Derivation of the model equations is not included. ( SPICE is a circuit sim ulation program available from EECS Industrial Support Office, 461 Cory Hall, University of Cali­ fornia, Berkeley, CA 94720. ) Acknowledgements I wish to express my gratitude to Valid Logic Systems, Inc.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Circuit Simulation

Abstract
A simulator implements test instrumentation in software. With simulation, a designer troubleshoots a design by probing various circuit nodes as if checking out a physical board or chip with an oscilloscope. In other words, the design is analyzed and verified by displaying waveform and timing information — but without having to build the circuit. Designers who want to reduce prototyping time and shorten design cycles should be simulating their circuits. Besides the obvious advantage of fewer prototype cycles and greatly reduced development costs, designs that have undergone simulation are typically of higher quality. In other words, simulation makes it easier to optimize a design. And when the design is optimized, the transition to manufacturing is much smoother.
Dileep Divekar

Chapter 2. Device Modeling

Abstract
Models describe the device behavior to the circuit simulation program. This is usually done by expressing the currents and charges associated with the device terminals in terms model equations. A device model can be used for a variety of different purposes and ideally it would be convenient to have only one model which can serve all the needs. However, different applications place different requirements on the model and many times these prove to be contradictory constraints necessitating some compromises.
Dileep Divekar

Chapter 3. Diode Models

Abstract
Although diode is not a field effect device, it is part of the parasitics associated with the field effect devices. Field effect devices have junction diodes which are not part of the intrinsic device but are part of the parasitic components which need to be included in the model. This chapter describes the diode model suitable fo this purpose. This model is simpler than the model implemented as a general diode model in many of the circuit simulation programs. The general diode model includes parasitic series resistance effects and reverse bias breakdown effects which are not modeled for the parasitic diodes. For normal device operation, the parasitic diodes are supposed to be reverse biased and their contribution to the device characteristics is normally negligible. Hence there is no need to use a complicated model.
Dileep Divekar

Chapter 4. Jfet Models

Abstract
The junction field effect transistor (JFET) is basically a voltage controlled resistor [15]. Because its conduction process involves predominantly one kind of carrier, the JFET is called a “unipolar” transistor to distinguish it from the bipolar junction transistor (BJT), in which both types of carriers are involved.
Dileep Divekar

Chapter 5. Mosfet Models

Abstract
The metal-oxide-semiconductor field-effect transistor (MOSFET) is the most important device for very-large-scale integrated circuits such as microprocessors and semiconductor memories. MOSFET is also becoming an important power device. Because the current in a MOSFET is transported predominantly by carriers of one polarity only (e.g., electrons in an n-channel device), the MOSFET is referred to as a unipolar device. Although MOSFETs have been made with various semiconductors such as Ge, Si, GaAs, and use various insulators such as SiO2, Si3N4, and Al2O3, the most important system is the Si-SiO2 combination [15].
Dileep Divekar

Chapter 6. Mesfet Models

Abstract
The operation of a metal-semiconductor field-effect transistor (MESFET) is identical to that of a JFET. In the MESFET, however, a metal-semiconductor rectifying contact is used for the gate electrode instead of a p-n junction. The MESFET offers certain processing and performance advantages, such as low temperature formation of the metal-semiconductor barrier (as opposed to a p-n junction made by diffusion or grown processes), low resistance and low IR drop along the channel width, and good heat dissipation for power devices (the rectifying contact can also serve as an efficient thermal contact to heat sink).
Dileep Divekar

Backmatter

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