File Name: circuits systems and signal processing .zip
Introduction to electronic systems 1. However, we usually mean apparatus and systems which use devices which amplify and process electrical signals, and which need a source of power in order to work. Most of the devices which do this are transistors. In the early days of electronics, the devices were vacuum-tubes 'valves' in which a stream of electrons was emitted from a heated cathode, via a control grid, towards an anode. This is probably where the name 'electronics' came from. Beams of electrons in a vacuum are still used in the cathode-ray tubes used for displays in television receivers and computer monitors, and in microwave devices called magnetrons and travelling-wave tubes.
The electrical signal from a microphone is an example of an analog signal; its waveform graph of voltage against time has a similar shape to the waveform of the sound waves which it 'picks up'. The converse process, that of converting an electrical signal into a sound wave, also involves analog signals. The electrical analog signal is fed to a loudspeaker, which produces a sound waveform which is an analog of the original sound. An example of a digital signal is that recorded on a compact disc CD.
If an analog signal from a microphone is to be recorded, then it must first be converted to digital form. This involves sampling the analog signal at a frequency much higher than the highest analog signal frequency, and then converting the sample amplitudes into corresponding digital codes represented by a series of electrical pulses. Further coding is used, first to 'compress' the total data and then to convert it into longer sequences for immunity against corruption.
These sequences are stored on the disc as tiny 'blips' representing binary data. All of the digital circuits use transistors, in sub-circuits called gates and flip-flops.
So, both types of electronics have transistors in common. The design of the gate and flip-flop circuits, for ever-higher speed and lower power dissipation, depends heavily on the same circuit concepts as the analog circuits designed for higher frequencies and lower power dissipation.
These are concepts such as the equivalent circuit of the transistor, stored charge, stray capacitance and inductance, input and output impedance, electrical noise and the Uke. Interconnections between sub-assemblies, whether for digital signals in the form of pulses, or for analog signals, must be designed with a knowledge of transmission line theory when high frequencies or high data rates which incur high frequencies are present.
So, a great deal of the analog material of this book forms also the basic material of digital circuit design. The analog signal processing in the book is mirrored in digital signal processing, much of which is modelled on analog prototypes, and uses the same design theory, modified for digital implementation.
Thus, a good grounding in the theory of analog electronics is not only useful in its own right, but provides much of the background skills for the design of digital systems. The following examples illustrate the roles of analog and digital electronics in various systems. Figure 1. Each microphone converts sound waves into an electrical voltage, or electrical signal, which represents the sound. The electrical signals are conveyed by cables to an ampUfier which boosts, or amplifies, the signals before passing them by cables, or radio, to the loudspeakers.
The loudspeakers convert the electrical signals back into sound waves which, ideally, are the same as the original speech or music but at much higher intensities. In Figure 1. The waveform of the electrical voltage v generated by the microphone has an almost identical shape. It is analogous to the sound waveform, so it is called an analog waveform, or analog signal. The microphone waveform has a typical peak voltage of some millivolts. The typical peak voltages needed to provide enough sound from the loudspeakers in a concert hall are a few volts, or tens of volts.
So it is quite obvious that the microphone signal voltages need to be amplified by a factor of about one thousand or more. The amplifier has to have a voltage gain of about one thousand or more. Suppose the signal from the microphone has a peak voltage of 10 mV, and the required output voltage from the ampUfier is 20 V.
What voltage gain is needed?. Loudspeakers have input impedances of one of a few standard values, such as 4 fi, 8 Q, or 15 O. So a speaker input voltage of a few volts, or tens of volts, causes an input power of several watts.
Suppose the input was a sine wave of 20 V rms, and the speaker input impedance appeared purely resistive with a value of 8 fi. What would be the input power? The analog voltage from each microphone is increased in voltage by the ampUfier, but it is still an analog of the original sound, and it is this boosted analog signal which is fed to the loudspeakers.
So, Figure 1. In a typical hi-fi high fideUty system, some of the components use analog signals, and some use digital. All these recorded the sound as a side-to-side displacement of a groove in the surface; a visible graph, or analog, of the sound waveform.
Records are played back by a pick-up in which a 'stylus' sometimes called a 'needle' rides in the groove. Its side-to-side displacement produces an analog output voltage from the pick-up.
Inevitably, wear and dust in the groove, and surface scratches, lead to 'surface noise', a problem which is largely avoided in CDs.
Audio-tape cassettes were a much later development. As in the earlier reel-to-reel technique, the sound is recorded as a magnetic analog signal on magnetic tape. In recording, the electrical signal from the microphone is fed to a coil called the recording head. This generates a varying magnetic field which induces a pattern of permanent magnetism in the magnetic coating on the tape as it passes over the recording head.
On playback, the tape passes over the same head, causing a varying magnetic field which induces a varying voltage in the coil. Again the output is an analog voltage, and again it can suffer from noise. The 'tape noise' is caused by the granularity of the magnetic coating.
The CD is digital. The CD player picks up the digital signal from the CD, decodes it, and converts it back to an analog signal representing the original recorded sound.
The digital signal on the CD consists of a series of 'pits' etched into a layer of the disc just below the surface.
These pits represent the noughts and ones of a binary code which, in turn, represents the analog signal from the microphone which picked up the original sound. The analog-todigital and the digital-to-analog conversion processes are described in Chapter 7.
The tiny pits representing the binary-coded signal can easily be obscured by surface dust, finger-prints and the Hke, which cause errors in the recovered digital signal. However, because of the coding process, a great many errors can be tolerated before the decoded digital signal is corrupted. The output from the CD player is an analog signal with a peak voltage of 1V or so, and with a very-low noise content.
It has a very-high signal-to-noise ratio. The radio tuner is a conventional radio, but without a power output stage. The latest types receive digital broadcasts, in which the audio signals are coded digitally before transmission. The electron-tube cathode ray type has been used in various forms since the early days of television, and is still used for high-quality work. The later-developed CCD type is Ughter and cheaper, and is used in 'camcorders', electronic news gathering ENG , 'webcams' for Internet use, surveillance, and digital cameras which record still pictures.
In the CCD camera, the observed scene is focussed, by a lens, onto an array of photosensitive devices, each forming one picture cell pic-cell or 'pixel' of the image. Each device is sensitive to the intensity of the light falling upon it, and generates a corresponding analog electric charge. To obtain an output signal from the array, the charges are transferred, or 'coupled', from pixel to pixel along each row of pixels, and from row to row, until all the charges have been read out as voltage variations.
This process is repeated at a rate of 25 times per second the European standard , or 30 times per second the American standard. The resulting analog signal is called a video signal. It is amplified by a video amplifier before passing to the output. In the cathode-ray camera, the image is focussed onto a photo-electric mosaic inside an evacuated glass tube.
A beam, or ray, of electrons is emitted from a heated cathode, and is scanned across the image, pixel by pixel, in the same 'raster' pattern as in the CCD camera. The different charges on the pixels vary the electron-beam current as the beam is scanned. This current passes through a load resistor and causes a varying video analog output voltage. Colour cameras of both types use either three monochrome cameras, each with a colour filter in its hght path, or one photo-sensitive array of pixels, each of which comprises three elements, one for each of three colours.
The colours used are the three primary colours for additive mixing : red, green and blue. The colour video signal comprises the outputs of these three cameras. In camcorders, these colour signals are combined to form one 'composite' video signal, which can be recorded on the internal videotape or connected directly to the video input of a television receiver.
In digital camcorders, the video signal is first digitized before recording on the tape. On play-back the digital signal is converted back to analog form. For broadcast television, the composite video signal, together with the sound signal, is made to 'modulate' a high-frequency radio 'carrier' signal which is then transmitted. Modulation is described in Chapter 9. Clearly, this signal must be conditioned or converted to provide either an analog voltage proportional to angular position, or a digital signal corresponding to angular position.
The rotating shaft carries a disc into which radial slots are cut. A small lamp is positioned on one side of the disc, and a Hght-sensitive device, such as a photo-diode, is positioned on the other side. As the disc rotates, the lamp shines through each slot in turn and onto the light-sensitive device, which produces corresponding voltage pulses.
These pulses can be counted to indicate the total angular displacement, or increment, of the shaft.
Livre chevalier dessin industriel pdf. Skoda kodiaq preise pdf. Zwcad tudo sobre pdf. A escolhida jimena cook pdf. Italian visa application guidelines pdf. Key elements of the signal path include preamplifiers, analog signal processors, data converters to and from digital, and— when the signal is in digital form— a digital processor. Pdf this paper presents some critical analysis of the current trends in teaching circuits, systems and signal processing.
Signal Processing is one of the large specializations in electrical engineering, mechanical engineering and computer sciences. It derives input from physics, mathematics and is an indispensable feature of all natural- and life sciences in research and in application. The snew series "Advanced Issues on Signals, Systems and Devices" presents original publications mainly from speakers on the International Conferences on Signal Systems and Devices but also from other international authors.
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