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A 50-ohm cable? TRANSMISSION LINES 2008-09-02 10:32:43 Early in my explorations of electricity, I came across a length of coaxial cable with the label “50 ohms” printed along its outer sheath. (Figure below) Now, coaxial cable is a two-conductor cable made of a single conductor surrounded by a braided wire jacket, with a plastic insulating material separating the two. As such, the outer (braided) conductor completely surrounds the inner (single w
Circuits and the speed of light TRANSMISSION LINES 2008-09-02 10:32:13 Suppose we had a simple one-battery, one-lamp circuit controlled by a switch. When the switch is closed, the lamp immediately light
s. When the switch is opened, the lamp immediately darkens: (Figure ) Lamp appears to immediately respond to switch. Actually, an incandescent lamp takes a short time for its filament to warm up and emit light after receiving an electric current of suff Read more:Circuits
Characteristic impedance TRANSMISSION LINES 2008-09-02 10:31:42 Suppose, though, that we had a set of parallel wires of infinite length, with no lamp at the end. What would happen when we close the switch? Being that there is no longer a load at the end of the wires, this circuit is open. Would there be no current at all? (Figure ) Driving an infinite transmission line. Despite being able to avoid wire resistance through the use of superconduct
Finite-length transmission lines 2008-09-02 10:31:05 A transmission line of infinite length is an interesting abstraction, but physically impossible. All transmission lines have some finite length, and as such do not behave precisely the same as an infinite line. If that piece of 50 Ω “RG-58/U” cable I measured with an ohmmeter years ago had been infinitely long, I actually would have been able to measure 50 Ω worth of resistance between the
``Long'' and ``short'' transmission lines 2008-09-02 10:30:10 In DC and low-frequency AC circuits, the characteristic impedance of parallel wires is usually ignored. This includes the use of coaxial cables in instrument circuits, often employed to protect weak voltage signals from being corrupted by induced “noise” caused by stray electric and magnetic fields. This is due to the relatively short timespans in which reflections take place in the line, as
Standing waves and resonance TRANSMISSION LINES 2008-09-02 10:29:28 Whenever there is a mismatch of impedance between transmission line and load, reflections will occur. If the incident signal is a continuous AC waveform, these reflections will mix with more of the oncoming incident waveform to produce stationary waveforms called standing waves. The following illustration shows how a triangle-shaped incident waveform turns into a mirror-image reflection upon r Read more:Standing
Impedance transformation TRANSMISSION LINES 2008-09-02 10:28:26 Standing waves at the resonant frequency points of an open- or short-circuited transmission line produce unusual effects. When the signal frequency is such that exactly 1/2 wave or some multiple thereof matches the line's length, the source “sees” the load impedance as it is. The following pair of illustrations shows an open-circuited line operating at 1/2 (Figure below) and 1 wavelength (Fig
Active versus passive devices AMPLIFIERS AND ACTIVE DEVICES 2008-09-02 10:26:42 An active device is any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity). In order for a circuit to be properly called electronic, it must contain at least one active device. Components incapable of controlling current by means of another electrical signal are called passive devices. Resistors, capacitors, inductors, transforme Read more:versus
Amplifiers AMPLIFIERS AND ACTIVE DEVICES 2008-09-02 10:26:06 The practical benefit of active devices is their amplifying ability. Whether the device in question be voltage-controlled or current-controlled, the amount of power required of the controlling signal is typically far less than the amount of power available in the controlled current. In other words, an active device doesn't just allow electricity to control electricity; it allows a small amount of Read more:Amplifiers
Amplifier gain AMPLIFIERS AND ACTIVE DEVICES 2008-09-02 10:24:58 Because amplifiers have the ability to increase the magnitude of an input signal, it is useful to be able to rate an amplifier's amplifying ability in terms of an output/input ratio. The technical term for an amplifier's output/input magnitude ratio is gain. As a ratio of equal units (power out / power in, voltage out / voltage in, or current out / current in), gain is naturally a unitless measur Read more:Amplifier
Decibels AMPLIFIERS AND ACTIVE DEVICES 2008-09-02 10:24:18 In its simplest form, an amplifier's gain is a ratio of output over input. Like all ratios, this form of gain is unitless. However, there is an actual unit intended to represent gain, and it is called the bel. As a unit, the bel was actually devised as a convenient way to represent power loss in telephone system wiring rather than gain in amplifiers. The unit's name is derived from Alexander
Absolute dB scales AMPLIFIERS AND ACTIVE DEVICES 2008-09-02 10:23:41 It is also possible to use the decibel as a unit of absolute power, in addition to using it as an expression of power gain or loss. A common example of this is the use of decibels as a measurement of sound pressure intensity. In cases like these, the measurement is made in reference to some standardized power level defined as 0 dB. For measurements of sound pressure, 0 dB is loosely defined as th Read more:Absolute
Attenuators AMPLIFIERS AND ACTIVE DEVICES 2008-09-02 10:23:08 Attenuators are passive devices. It is convenient to discuss them along with decibels. Attenuators weaken or attenuate the high level output of a signal generator, for example, to provide a lower level signal for something like the antenna input of a sensitive radio receiver. (Figure below) The attenuator could be built into the signal generator, or be a stand-alone device. It could provide a fix
Introduction SOLID-STATE DEVICE THEORY 2008-09-02 10:20:41 This chapter will cover the physics behind the operation of semiconductor devices and show how these principles are applied in several different types of semiconductor devices. Subsequent chapters will deal primarily with the practical aspects of these devices in circuits and omit theory as much as possible. Read more:Introduction
Quantum physics SOLID-STATE DEVICE THEORY 2008-09-02 10:20:08 To say that the invention of semiconductor devices was a revolution would not be an exaggeration. Not only was this an impressive technological accomplishment, but it paved the way for developments that would indelibly alter modern society. Semiconductor devices made possible miniaturized electronics, including computers, certain types of medical diagnostic and treatment equipment, and popular te
Valence and Crystal structure SOLID-STATE DEVICE THEORY 2008-09-02 10:19:21 Valence: The electrons in the outer most shell, or valence shell, are known as valence electrons. These valence electrons are responsible for the chemical properties of the chemical elements. It is these electrons which participate in chemical reactions with other elements. An over simplified chemistry rule applicable to simple reactions is that atoms try to form a complete outer shell of 8 elec Read more:Crystal
The P-N junction SOLID-STATE DEVICE THEORY 2008-09-02 10:17:28 If a block of P-type semiconductor is placed in contact with a block of N-type semiconductor in Figure below(a), the result is of no value. We have two conductive blocks in contact with each other, showing no unique properties. The problem is two separate and distinct crystal bodies. The number of electrons is balanced by the number of protons in both blocks. Thus, neither block has any net charg
Junction diodes SOLID-STATE DEVICE THEORY Junction diodes SOLID-STATE DEVICE THEORY 2008-09-02 10:16:58 There were some historic crude, but useable semiconductor rectifiers before high purity materials were available. Ferdinand Braun invented a lead sulfide, PbS, based point contact rectifier in 1874. Cuprous oxide rectifiers were used as power rectifiers in 1924. The forward voltage drop is 0.2 V. The linear characteristic curve perhaps is why Cu2O was used as a rectifier for the AC scale on D'Ar Read more:Junction
Insulated-gate field-effect transistors (MOSFET) SOLID-STATE DEVICE THEORY 2008-09-02 10:15:10 The insulated-gate field-effect
transistor (IGFET), also known as the metal oxide field effect transistor (MOSFET), is a derivative of the field effect transistor (FET). Today, most transistors are of the MOSFET type as components of digital integrated circuits. Though discrete BJT's are more numerous than discrete MOSFET's. The MOSFET transistor count within an integrated circuit may approach th
Thyristors SOLID-STATE DEVICE THEORY 2008-09-02 10:14:32 Thyristors are a broad classification of bipolar-conducting semiconductor devices having four (or more) alternating N-P-N-P layers. Thyristors include: silicon controlled rectifier (SCR), TRIAC, gate turn off switch (GTO), silicon controlled switch (SCS), AC diode (DIAC), unijunction transistor (UJT), programmable unijunction transistor (PUT). Only the SCR is examined in this section; though the
Semiconductor manufacturing techniques SOLID-STATE DEVICE THEORY 2008-09-02 10:13:29 The manufacture of only silicon based semiconductors is described in this section; most semiconductors are silicon. Silicon is particularly suitable for integrated circuits because it readily forms an oxide coating, useful in patterning integrated components like transistors. Silicon is the second most common element in the Earth's crust in the form of silicon dioxide, SiO2, otherwise known as Read more:Semiconductor
Superconducting devices SOLID-STATE DEVICE THEORY 2008-09-02 10:12:43 Superconducting devices, though not widely used, have some unique characteristics not available in standard semiconductor devices. High sensitivity with respect to amplification of electrical signals, detection of magnetic fields, and detection of light are prized applications. High speed switching is also possible, though not applied to computers at this time. Conventional superconducting device
Quantum devices SOLID-STATE DEVICE THEORY 2008-09-02 10:12:15 Most integrated circuits are digital, based on MOS (CMOS) transistors. Every couple of years since the late 1960's a geometry shrink has taken place, increasing the circuit density– more circuitry at lower cost in the same space. As of this writing (2006), the MOS transistor gate length is 65-nm for leading edge production, with 45-nm anticipated within a year. At 65-nm leakage currents were be
Tutorial - How Lightning Works? 2008-09-20 02:01:24 How lightning works?clouds causes the charges to separate, there is a conductive path.Lightning and atmospheric electricitya historical essay on lightning research, access to data from the lighting teams, learn about LIS, OTD, LMS, an overview of field programs. Museum of electricity - Lightningwhat causes lightning?, what causes thunder?, the global electric circuit.Lightning weather eyewhat is l Read more:Tutorial
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