December 2010
Intermediate to advanced
424 pages
11h
English
CHAPTER TWO
Resistors, Capacitors, and Inductors
2.1 INTRODUCTION
At radio frequencies, passive circuit elements typically have a more complicated model than those used in lower frequency designs. The simple resistor, capacitor, or inductor cannot be counted on to provide a pure resistance, capacitance, or inductance in high-frequency circuits. Usually the “lumped” element is best modeled as a combination of these pure elements. In addition, when the size of the element becomes larger than 0.1 wavelength in the circuit medium, the equivalent circuit may also include transmission lines.
2.2 RESISTORS
Integrated circuit resistors can be classified into three groups: (1) semiconductor films, (2) deposited metal films, and (3) cermets (a mixture of metal and dielectric materials). Of these, only the first two have found widespread use in high-frequency circuits. Semiconductor films can be fabricated by diffusion into a host semi-insulating substrate by depositing a polysilicon layer or by ion implantation of impurities into a prescribed region. Polysilicon, or polycrystalline silicon, consists of many small submicron crystals of silicon with random orientations.
2.2.1 Resistor Types
The resistance value of an integrated circuit resistor depends on the conductivity of the channel through which the current is flowing. In the diffused resistors in a semiconductor substrate, the conductivity is a function of the doping concentration and the carrier mobility. The conductivity is
(2.1)
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