Skip to main content Accessibility help
×
  1. Home
  2. Browse subjects
  3. Engineering
  4. Circuits and systems
  5. Content listing

Refine search

Refine search

Access:
Content type:
Publication date:
Apply   From and To filters
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Save to Kindle
  • Save to Dropbox
  • Save to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

1808 results in Circuits and systems

Page 81 of 91

  • 8 - Transistor Switches

  • David Rutledge, California Institute of Technology
  • Book:
    The Electronics of Radio
    Published online:
    05 August 2012
    Print publication:
    13 August 1999, pp 142-153

  • Summary

    Now we begin the study of transistor circuits. Transistors have three terminals. Usually one of the terminals is the input, another is the output, and the third is a common connection that is shared between the input and the output. Transistor circuits can increase the power of a signal. For this they require an additional DC power source. Circuits that increase power are called active circuits. By comparison, a passive circuit has loss. The filters we covered in the earlier chapters are examples of passive circuits. We will study several different active circuits. An amplifier increases the power of a signal without changing the frequency. In an oscillator, an output sine wave is generated without any input signal. Transistors can also be used in passive circuits. In Problem 5, we saw that a transistor could act as a fast switch, with either a low resistance between the output terminals or a high resistance, depending on the input voltage. We will also use a transistor as a variable attenuator to control the signal level.

    Manufacturers can combine many transistors on one chip of silicon. These circuits are called integrated circuits, or ICs. Many thousands of different integrated circuits are available. One common type of IC includes several amplifiers cascaded one after another, so that the output signal is much larger than the input. These circuits are called op amps, short for operational amplifiers.

  • 2 - FM receivers

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 49-108

  • Summary

    Superheterodyning revisited

    Just as the superheterodyne receiver dominates AM receiver design, so it dominates FM receiver design and has done so since its infancy. It is interesting to note that Major Edwin Armstrong, who invented the superheterodyne principle, also invented FM. This invention arose from his investigation of the causes and elimination of noise in AM receivers.

    Because the frequency spectrum of FM is so much wider than that for AM, the FM band is placed much higher in the frequency spectrum. Broadcast FM stations are assigned frequency slots 0.2 MHz wide - 20 times that for commercial AM. These stations have carrier frequencies between 87.9 and 107.9 MHz. Thus both the AM and FM broadcast bands will accommodate about 100 discrete channels. The IF frequency used for broadcast FM receivers is 10.7 MHz.

    As was the case for AM, it will be instructive to look at the spectral energy diagram for sinusoidal modulation (Fig. 2.1). As was also the case for AM, the mixing process results in two complete FM signals. The difference frequencies are clustered about 10.7 MHz and pass on into the IF amplifier.

    Exercise 2.1 Assuming the station tuned to has a carrier at 99.3 MHz, find the frequency about which the sum frequencies are clustered.

    As might be expected, the sum frequencies are eliminated by the tuned amplifier. All of the original FM information is thus in the IF signal.

    The limiting principle

    Because all of the information in an FM signal is encoded as frequency variation, it is a foregone conclusion that any variation of amplitude represents noise. This source of noise can be virtually eliminated by passing the FM signal through a limiter prior to detection. A simple and effective limiter consists of an amplifier stage driven to saturation on one polarity of signal swing and cutoff on the other polarity. There will be, of course, a finite slope to the rise and fall of the squaredoff output, but the greater the overdrive the FM signal presents to the limiter, the more nearly square will be its output. Limiters are also cascaded to give more perfect (or harder) limiting.

    The FM detector principle

    FM detectors are usually called discriminators or demodulators. Unlike AM, where the form of the detector is almost universal, there is a wide variety of workable FM detectors.

  • 1 - AM receivers

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 1-48

  • Summary

    The crystal set

    From both the conceptual and historical points of view, our study of AM receivers must start with the “crystal set.” This is the simplest AM receiver, consisting of only three essentials: a tuned circuit, a detector, and a transducer (usually headphones or an earphone) to provide sound output. A simple crystal set schematic is shown in Fig. 1.1. To get usable volume, it is generally necessary to use a long (50 or more) antenna and an earth ground. The capacitor is variable so that the parallel resonant tuned circuit composed of it and the inductance L can tune over the AM broadcast band (535-1,705 kHz). Two types of variable capacitors used for tuning are shown in Fig. 1.2.

    Exercise 1.1 A once-common variable capacitor has a maximum capacitance of 365 pF.

    (a) What must the inductance be if the receiver is to tune the entire AM band?

    (b) What must the minimum value of the variable capacitance be to tune the entire AM band?

    The sound section of any consumer electronic equipment is referred to as audio, and the amplifier that amplifies electrical signals in the range of human hearing is called an audio amplifier.

    The diode in Fig. 1.1 demodulates the audio signal from the AM carrier and feeds it into the headphones.

    The crystal set has two serious shortcomings: poor selectivity and poor sensitivity. Selectivity is the ability to separate two stations whose carrier frequencies are close together - especially if one of them delivers significantly more signal to your antenna than the other. If you thought upon reading this definition that selectivity must depend on the Q of the tuned circuit, you are absolutely correct.

    Sensitivity is a measure of how strong a signal must be delivered to the antenna for a radio to receive it properly. It is usually expressed in /∧volts/meter needed to drive the radio receiver to full output for AM. For FM, it is usually given as /xvolts needed for full quieting. Note that for AM the units of sensitivity are those of electric field. In other words, the sensitivity specification is a measure of the E field strength of the station's transmitted electromagnetic wave needed by the receiver's antenna.

  • 10 - Telephones

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 509-542

  • Summary

    Until the FCC removed the ban on connecting non-AT&T equipment to the phone lines, few people would have thought of the telephone as a consumer electronic item. Now, however, there can be little doubt that it is one. Not only did this decision unchain the creative genius of free enterprise, but it coincided in time with the emerging availability of inexpensive MSI and LSI chips. The result has been a proliferation of phones and features undreamed of just twenty years ago. The Bell System's development of Touch-Tone® dialing led to the development of the DTMF (dual-tone, multi-frequency) encoder and, later, decoder chips. Sharply declining prices on digital memory chips led to their incorporation in many phones for phone number storage and rapid dialing. Phones with memory may be broken down into three groups:

  • (1) Those that can store just a single number - the last one dialed. If that number is busy, it can be redialed with a single button.

  • (2) Those that store two to ten numbers. These numbers can be dialed by pushing just one of the digit buttons.

  • (3) Those that can store more than ten numbers. These numbers can be dialed only by pressing two buttons in sequence to form a two-decimaldigit code.

    • Anyone who has ever listened to a phone conversation where the speaker tried to make a comment while covering the receiver with his hand knows that this does a very poor job of masking the sound. It is therefore surprising that a concept as simple as the privacy or mute switch did not come into wide use until the lines were made available to all equipment that met phone company specifications.

    Speakerphones have existed for some time, but they tended to be prone to acoustic feedback. Current versions, however, electronically sense where the input is coming from and open the channel only in the direction it needs to go. When the speaker changes, signal flow in the opposite direction is enabled.

    Cordless phones have benefited from inexpensive transmitter and receiver ICs and have declined in price to where they are now a popular option. They are almost too popular, in fact. In some wealthy neighborhoods, there have been so many cordless phones that two related problems have become evident. The first is interference between phones, and the second is eavesdropping.

  • 8 - Video cassette recorders

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 345-458

  • Summary

    Although recorders capable of recording a TV signal on magnetic tape have been available since the early 1950s and vidéocassette recorders have been since the early 1970s, they never became a consumer item until 1975, when Sony introduced the Betamax VCR. Earlier units were generally too complex, too expensive, and too voracious in their appetite for tape. The first Betamax units could record for one hour on a cassette, making them almost as easy to use as an audio tape recorder. Two years later, Matsushita introduced the VHS (Video Home System) VCR, which boasted recording times of two or four hours on a somewhat larger cassette. The Betamax system was then modified to allow two hours of recording. Subsequently VHS achieved a six-hour record time and Beta got up to three hours. For both machines, the longer record time yielded slightly inferior picture quality relative to the shorter record times. Although both systems used the same general principles in their electronics, they were not compatible either mechanically or electrically. If both systems were played at their fastest speed (one-hour play time for Beta; two hours for VHS), the Beta probably produced a slightly better picture quality, but if both were operated in the two-hour mode, the VHS picture was generally better. The fundamental reason for this is that the Beta cassette is smaller and simply cannot hold as much tape as the VHS cassette does. Thus the Beta achieved the two- and threehour modes by slowing down the tape speed. This hurt high-frequency response and so picture details were lost.

    Although there were a number of more esoteric differences between the Beta and VHS systems such as tape tension (Beta lower in record and playback; VHS lower in fast forward and reverse), it can hardly be maintained that the chief issue in the minds of most consumers was anything but the longer record time of the VHS. This led to the situation in 1985 that all manufacturers of the Beta system except Sony had either switched to the VHS system or were “hedging their bets” by manufacturing both VHS and Beta systems. The dominance of VHS over Beta is now total. Virtually no tapes are produced in Beta format any longer. For these reasons, we will direct our attention exclusively to the VHS system.

  • 6 - Monochrome TV

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 171-252

  • Summary

    Monochrome or black & white (B/W) TV signals are transmitted by very few stations now. It is still well worth our while, however, to understand monochrome TV. There are several reasons for this:

  • (1) B/W TV circuitry is a subset of color TV circuitry. If we understand it, we have a 100%-usable foundation for understanding color.

  • (2) Although B/W transmission is rare, B/W receivers are still manufactured. It is with such receivers that we concern ourselves in this chapter. In Section 6.4 we analyze one of the VLSI chips that makes such receivers so economical. Color signals are compatible with B/W receivers because the receiver circuitry simply ignores the color information.

  • (3) The mechanisms of picture (video) signal generation and picture formation are much simpler in monochrome sets.

    • The nature of monochrome TV signals

    The television principle

    The picture to be transmitted is focused onto a small photosensitive area. One very small area within the photosensitive device called a pixel (picture element) is probed by a finely focused electron beam, which generates a signal dependent on the light intensity at the point of impact. The exact mechanisms involved in this process are well covered in many books for a variety of imaging devices (e.g., Neuhauser and Cope, 1992). In solid-state imaging arrays, the pixel is addressed digitally rather than by means of an electron beam.

    In either case, the end result is the same. The output voltage associated with each pixel is a single-valued function of the light intensity at that pixel. Having determined the light level at that pixel, another pixel - usually an adjacent one - is checked to determine its light level. This process continues over the whole screen until every pixel on it has been evaluated. Then the process starts all over again. The sequence of analog voltage levels corresponding to the pointby- point illumination levels is called the video signal. It should be obvious that we must know the light level at every pixel, in order to reproduce the picture. The video signal contains just that information and yet, by itself, it is useless. A little thought will show why this is so. If we have the video signal, we could use its value at a given moment to determine the light level at a pixel on the display device - but which pixel?

  • 3 - Modern receiver circuitry

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 109-121

  • Summary

    As indicated in the introduction, new types of receivers and receiver circuitry are being introduced continually. In this chapter we will look at some of them.

    An integrated AM/FM receiver

    The receiver we consider here is one of the Sony Walkman series that is designed to drive lightweight stereo headphones rather than a speaker. The headphones are so intrinsic to the design that their cord also serves as the FM antenna! The schematic is shown in Fig. 3.1.

    We begin by directing our attention to the lower right-hand corner of the schematic. Rather than returning one headphone lead from each channel directly to ground, the ground return for both channels is through L7. This has a reactance of about 1.4 kΩ in the FM band but less than an ohm for audio frequencies. Thus one side of each headphone is AC grounded for audio, but a significant FM signal is developed across L7 and coupled via C39 to the RF input of the receiver. This capacitor's reactance is less than 50Ω in the FM band. Diodes D1 and D2 serve to prevent overdriving IC1. For reception of distant FM stations, Sl-1 couples the FM antenna circuitry directly to a bandpass filter. For local reception, the coupling is via R16, which attenuates the larger local signals. In the AM position, C1 AC grounds any FM signal received by the FM antenna. The DC potential on this line is .85 V for FM, but it gets pulled down to zero in the AM position of 57-7. This line is tied to the internal voltage regulator of 1C1 and may be a shutdown line. The 3 V input to the regulator (pin 26 of IC1) provides a regulated 1.3 V output on pin 8 when the voltage on pin 15 is at the normal value of .85 V (for FM). When pin 15 is grounded in the AM position, the regulator output shuts down, removing supply voltage from the FM front-end portion of 1C1. This supply line is bypassed to ground by C2 and C40. The grounded end of each of the parallel tuned circuits is returned to this 1.3 V regulated supply line. Therefore, they are AC grounded but not DC grounded. This is analogous to the ZN414 TRF 1C receiver of Chapter 1.

  • 9 - Digital audio

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 459-508

  • Summary

    The strongest trend in consumer electronics at present is to encode analog signals to digital and record and process them digitally. The consumer unit must then decode the recorded digital data to output what is in most respects an excellent approximation to the original analog signal.

    Video discs

    Unlike magnetic tape technology, which began with audio machines (Chapter 5) and was extensively upgraded to accommodate video (Chapter 8), digital discs began with video and were then downscaled to audio.

    The first digital video disc player hit the market in 1978. There were two main technologies available in the players. Each of them required its own type of disc. Each type of disc had pits on it to differentiate between logic “ 1 ” and “0.” Some of the players had the pits embedded in a groove to facilitate reading by a stylus, whereas others used a dynamic tracking technique that required no grooves.

    The two main technologies were the optical pickup system and the capacitance pickup system. Optical pickups use a dynamic tracking laser system to read an ungrooved disc. The “read” mechanism never touches the disc. Capacitance pickups sensed the change in capacitance between a conductive pickup element and a slightly conductive record surface. When the pickup element was over a pit, there was less capacitance. This changed the frequency of an oscillator. The frequency changes were discriminated to produce logic levels. The discs for this type of system might or might not have grooves, but the “read” mechanism did contact the disc surface.

    In the U.S. market, the main contenders were the Philips (optical) and the RCA Selectavision (grooved-capacitance). Both produced excellent quality pictures. The RCA system had the advantages of lower price (about half that of optical systems) and an aggressive marketing of low-cost (<$20) video discs. The Philips system, which was produced by others as well, benefited from a public perception that discs read by a laser should last forever. Practically, this may be of little importance except to rental businesses. RCA tests showed that they could play a disc 100 times with no visible picture degradation. This is probably well over the lifetime enjoyment threshold for most people for most movies.

    As it turned out, however, all of the video disc technologies were pretty well overshadowed by the VCR (Chapter 8).

  • 7 - Color TV

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp 253-344

  • Summary

    The main issue at the inception of color TV broadcasting was again one of compatibility. The requirement that the color signal be usable by black-andwhite TV sets led to a system in which additional information was broadcast along with the previously used signals. This additional information was simply not processed by monochrome receivers. Compatibility also requires that a color set be able to receive a monochrome picture properly.

    To understand the characteristics that the color signal must have, it will help to digress and take a look at the color cathode-ray tube (CRT).

    The color CRT

    Even though the predominant color reproduction method used today is pretty much a “brute force” solution, it is at the same time, a testimonial to modern manufacturing techniques that it can be mass produced with the high degree of precision required to make it work.

    In the back of the neck of the CRT, arranged as shown in Fig. 7.1, are three electron guns instead of the single on-axis gun used in a B/W set. Even though these guns obviously don't shoot electrons of various colors, they are identified by the color they will cause on the screen. Instead of having a single (white) phosphor as in monochrome TV, the color CRT has three different phosphor colors on the inside face of the CRT. They are, in most cases, arranged in a dot pattern as shown in Fig. 7.2. The sets of dots enclosed in the triangular outlines include one of each color and are called triads. On a 19” (diagonal measurement) color CRT, the dots are about .38 mm in diameter. Between the dots and the gun assembly and close to the dots lies a sheet of metal called the shadow mask. There are holes in the shadow mask, positioned over the center of each triad of dots. The function of this mask is illustrated by Fig. 7.3, which shows only two guns and two dots. It can be readily perceived how the concept could be extended to three of each if the third spatial dimension were added.

    Note that although the vertical scale shown is the same for the dots and the guns, it is not the same as the horizontal scale.

  • Preface

  • Philip Hoff, California State University, Northridge
  • Book:
    Consumer Electronics for Engineers
    Published online:
    13 September 2019
    Print publication:
    28 July 1998, pp vii-xiv

  • Summary

    As far as this author is aware, this book blazes new ground. It covers a subject that has been much neglected in traditional electrical engineering education. As such, it may have value as a professional book, as well as serving its original purpose as a text. For such a book, it is mandatory that both the purpose of writing the book and the philosophy governing its structure be articulated.

    When I was in high school, I had a home-based business of repairing stereos, radios, and televisions. The knowledge to do this was obtained by reading various technician-level books and magazines on the subject and by experience obtained in the field.

    Upon beginning college as an electrical engineering (EE) major, I had eager expectations that the curriculum would teach the principles upon which the equipment worked. Alas, those expectations remained unfulfilled. The “real world” circuits, whose schematics a service technician is used to seeing, are generally far more complex than those in the electronics textbooks. I had a certain sense of having been cheated. Not until later did I realize that presenting simplified circuits in the electronics textbooks was thought of as an act of mercy by the textbook authors. It is obviously easier to understand a simplified circuit than a “real-world” one.

    This led to Phase II of this book's origins. After graduation I realized that an EE education at least provided the tools needed to understand consumer electronic circuits at a more advanced level. Commencing a career in college teaching gave additional impetus. A survey of seniors showed a great deal of interest in a course in consumer electronics. This led to a search for books that would give the information needed at the level of understanding desired. This search engendered disappointment of a different sort. The available materials, without exception, fell into three categories:

  • (1) The first type comprised technician-level books. These are generally the first information to be published on new consumer devices, but they are often fraught with errors and misconceptions.

  • (2) The second type of publication was written by engineers but was more like a reference handbook. Although some valuable information could be obtained from a few such books, they were not at all suitable as textbooks.

  • CHAPTER 3 - Linear Induction Actuators

  • I. Boldea, Polytechnic Institute, Timisoara, Romania, Syed A. Nasar, University of Kentucky
  • Book:
    Linear Electric Actuators and Generators
    Published online:
    19 September 2009
    Print publication:
    28 March 1997, pp 45-90

  • Summary

    Having given a general introduction to linear electric actuators in the preceding chapter, we now consider various types of LEAs in some detail. In this chapter, we begin with linear induction actuators (LIAs). These are essentially derived from rotary induction motors and resemble linear induction motors with restricted and controlled linear motion. Before we present an analysis of LIAs, it is worthwhile discussing some of the constraints under which these devices must operate.

    PERFORMANCE SPECIFICATIONS

    Linear induction actuators are used for short travel (between 2 and 3 m) and thus are characterized by rather small mechanical airgaps of about 1 mm. Also, the operating speed is generally less than 2 m/s. LIAs, as low-speed direct-drive systems, are characterized by the rated thrust Fxm for a given duty cycle and a peak (short-duration) thrust Fxp developed at standstill. LIAs are used only with variable-voltage variable-frequency static power converters or voltage-source inverters to obtain good energy conversion efficiencies and controlled thrust or positioning. The ac source—three-phase, in general—which supplies the static power converter is specified in terms of voltage and frequency: rated values and usual deviations. Few LIAs work continuously; short duty cycles are typical. In either case, the cooling system of the primary should also be specified as it determines the rated (design) current density in the LIA windings.

    The performance of the control system of the LIA must also be specified.

Page 81 of 91