Industrial Communication Systems

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Basic Semiconductor Physics (2nd edition)

Author : Chihiro Hamaguchi
Springer | English | 2010 | ISBN: 3642033024 | 570 pages | PDF | 10.3 MB

Description : 

This book presents a detailed description of the basic semiconductor physics. The reader is assumed to have a basic command of mathematics and some elementary knowledge of solid state physics. The text covers a wide range of important phenomena in semiconductors, from the simple to the advanced. The reader can understand three different methods of energy band calculations, empirical pseudo-potential, k.p perturbation and tight-binding methods. The effective mass approximation and electron motion in a periodic potential, Boltzmann transport equation and deformation potentials used for full band Monte Carlo simulation are discussed. Experiments and theoretical analysis of cyclotron resonance are discussed in detail because the results are essential to the understanding of semiconductor physics. Optical and transport properties, magneto-transport, two dimensional electron gas transport (HEMT and MOSFET), and quantum transport are reviewed, explaining optical transition, electron phonon interactions, electron mobility. Recent progress in quantum structures such as two-dimensional electron gas, superlattices, quantum Hall effect, electron confinement and the Landauer formula are included. The Quantum Hall effect is presented with different models. In the second edition, the addition energy and electronic structure of a quantum dot (artificial atom) are explained with the help of Slater determinants. Also the physics of semiconductor Lasers is described in detail including Einstein coefficients, stimulated emission, spontaneous emission, laser gain, double heterostructures, blue Lasers, optical confinement, laser modes, strained quantum wells lasers which will give insight into the physics of various kinds of semiconductor lasers, in addition to the various processes of luminescence.

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Backward Wave Oscillator (BWO)

Fig : Backward wave oscillator at Stockholm University operating in the Terahertz range.

A backward wave oscillator (BWO), also called carcinotron (a trade name for tubes manufactured by CSF, now Thales) or backward wave tube, is a vacuum tube that is used to generate microwaves up to the terahertz range. It belongs to the traveling-wave tube family. It is an oscillator with a wide electronic tuning range. An electron gun generates an electron beam that is interacting with a slow-wave structure. It sustains the oscillations by propagating a traveling wave backwards against the beam. The generated electromagnetic wave power has its group velocity directed oppositely to the direction of motion of the electrons. The output power is coupled out near the electron gun. It has two main subtypes, the M-type, the most powerful, (M-BWO) and the O-type (O-BWO). The O-type delivers typically power in the range of 1 mW at 1000 GHz to 50 mW at 200 GHz. Carcinotrons are used as powerful and stable microwave sources. Due to the good quality wavefront they produce (see below), they find use as illuminators in terahertz imaging. The backward wave oscillators were demonstrated in 1951, M-type by Bernard Epsztein and O-type by Rudolf Kompfner. The M-type BWO is a voltage-controlled non-resonant extrapolation of magnetron interaction, both types are tunable over a wide range of frequencies by varying the accelerating voltage. They can be swept through the band fast enough to be appearing to radiate over all the band at once, which makes them suitable for effective radar jamming, quickly tuning into the radar frequency. Carcinotrons allowed airborne radar jammers to be highly effective. However, frequency-agile radars can hop frequencies fast enough to force the jammer to use barrage jamming, diluting its output power over a wide band and significantly impairing its efficiency. Carcinotrons are used in research, civilian and military applications. For example, the Kopac passive sensor and Ramona passive sensor employed carcinotrons in their receiver systems.

Digital Signal Processing

Fig : Digital signal processors can manipulate and transform signals, such as sound, light, temperature or position and convert them to help us develop meaningful solutions to problems. For instance, the Analog-to-Digital converter can convert real-world signals and turn them into a digital format of 1's and 0's. The digital signal processor can then capture this digitized information and process it for real world application. This is done digitally at high speed at the receiver end or it can be converted to an analog format via a digital-to-analog converter application. The information we gain from digital signal processing can be used by a computer to control security, video compression, telephone and home theater systems. Digital signals can be compressed and transmitted faster and more efficiently from place to place, or enhanced to provide new information. By changing signals from analog to digital we gain the advantage of higher speed transmission as well as greater accuracy. We can also use DSP in other applications because it is programmable.

 

Digital signal processing (DSP) is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing. DSP includes subfields like: audio and speech signal processing, sonar and radar signal processing, sensor array processing, spectral estimation, statistical signal processing, digital image processing, signal processing for communications, control of systems, biomedical signal processing, seismic data processing, etc. The goal of DSP is usually to measure, filter and/or compress continuous real-world analog signals. The first step is usually to convert the signal from an analog to a digital form, by sampling and then digitizing it using an analog-to-digital converter (ADC), which turns the analog signal into a stream of numbers. However, often, the required output signal is another analog output signal, which requires a digital-to-analog converter (DAC). Even if this process is more complex than analog processing and has a discrete value range, the application of computational power to digital signal processing allows for many advantages over analog processing in many applications, such as error detection and correction in transmission as well as data compression. DSP algorithms have long been run on standard computers, on specialized processors called digital signal processor on purpose-built hardware such as application-specific integrated circuit (ASICs). Today there are additional technologies used for digital signal processing including more powerful general purpose microprocessors, field-programmable gate arrays (FPGAs), digital signal controllers (mostly for industrial apps such as motor control), and stream processors, among others.

Applications : 

The main applications of DSP are audio signal processing, audio compression, digital image processing, video compression, speech processing, speech recognition, digital communications, RADAR, SONAR, seismology and biomedicine. Specific examples are speech compression and transmission in digital mobile phones, room correction of sound in hi-fi and sound reinforcement applications, weather forecasting, economic forecasting, seismic data processing, analysis and control of industrial processes, medical imaging such as CAT scans and MRI, MP3 compression, computer graphics, image manipulation, hi-fi loudspeaker crossovers and equalization, and audio effects for use with electric guitar amplifiers.

Chemical Vapor Deposition

Fig : DC plasma (violet) enhances the growth of carbon nanotubes in this laboratory-scale PECVD apparatus.

Chemical vapor deposition (CVD) is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer (substrate) is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber. Microfabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon, carbon fiber, carbon nanofibers, filaments, carbon nanotubes, SiO2, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride, titanium nitride, and various high-k dielectrics. The CVD process is also used to produce synthetic diamonds.

EEE Short Questions and Answers (Digital Logic)

Fig : Basic Digital Logic Gates (Symbol)

1. Define AND Gate ?
ans : A logic gate that produces a HIGH output only when all of the inputs are HIGH.

2. What is an Inverter ?
ans : A logic circuit that inverts or complements its input.

3. What is a NOR gate ?
ans : A logic gate in which the output is LOW when one or more of the inputs are HIGH.

4. What is Timing Diagram ?
ans : A diagram of waveforms showing the proper timing relationship of all the waveforms.

5. What is XOR (Exclusive OR) gate ?
ans :  A logic gate that produces a HIGH output only when its two inputs are at opposite levels.

6. What is SPLD ?
ans : Simple programmable logic device; an array of AND Gates and OR Gates that can be programmed to achieve specified logic functions. Four types are PROM, PLA, PAL and GAL.

Phase Locked Loop (PLL)

Fig 1 : Block diagram of a PLL frequency multiplier

Phase Locked Loops (PLL) circuits are used for frequency control.  They can be configured as frequency multipliers, demodulators, tracking generators or clock recovery circuits. Each of these applications demands different characteristics but they all use the same basic circuit concept. Figure 1 contains a block diagram of a basic PLL frequency multiplier.  The operation of this circuit is typical of all phase locked loops.  It is basically a feedback control system that controls the phase of a voltage controlled oscillator (VCO). The  input signal is applied to one input of a phase detector.  The other input is connected to the output of a divide by N counter.  Normally the frequencies of both signals will be nearly the same.  The output of the phase detector is a voltage proportional to the phase difference between the two inputs.  This signal is applied to the loop filter.  It is the loop filter that determines the dynamic characteristics of the PLL.  The filtered signal controls the VCO.  Note that the output of the VCO is at a frequency that is N times the input supplied to the frequency reference input. This output signal is sent back to the phase  detector  via the divide by N counter. Normally the loop filter is designed to match the characteristics  required  by the application of the PLL. If the PLL is to acquire and track a signal the bandwidth of the loop filter will be greater than if it expects a fixed input frequency. The frequency range which the PLL will accept  and lock on is called the capture range.  Once the PLL is locked and tracking a signal the range of frequencies that the PLL will follow is called the tracking range. Generally the tracking range is larger than the capture range. The loop filter also determines how fast the signal frequency can change and still maintain lock. This is the maximum slewing rate.  The narrower the  loop filter bandwidth the smaller the achievable phase error.  This comes at the expense of slower response and reduced capture range.

Small-signal model

Fig : Small signal equivalent circuits (Photo Credit : Harvard University)

Small-signal modeling is a common analysis technique in electrical engineering which is used to approximate the behavior of nonlinear devices with linear equations. This linearization is formed about the DC bias point of the device (that is, the voltage/current levels present when no signal is applied), and can be accurate for small excursions about this point. Many electronic circuits, such as radio receivers, communications, and signal processing circuits, generally carry small time-varying signals on top of a constant bias. This suggests using a method akin to approximation by finite difference method to analyze relatively small perturbations about the bias point. Any nonlinear device which can be described quantitatively using a formula can then be 'linearized' about a bias point by taking partial derivatives of the formula with respect to all governing variables. These partial derivatives can be associated with physical quantities (such as capacitance, resistance and inductance), and a circuit diagram relating them can be formulated. Small-signal models exist for electron tubes, diodes, field-effect transistors (FET) and bipolar transistors, notably the hybrid-pi model and various two-port network.

• Large-signal DC quantities are denoted by uppercase letters with uppercase subscripts. For example, the DC input bias voltage of a transistor would be denoted V_IN.

• Small-signal quantities are denoted using lowercase letters with lowercase subscripts. For example, the input signal of a transistor would be denoted as v_in.

• Total quantities, combining both small-signal and large-signal quantities, are denoted using lower case letters and uppercase subscripts. For example, the total input voltage to the aforementioned transistor would be v_IN(t) = V_IN + v_in(t).

Transistor

Fig : Assorted discrete transistors. Packages in order from top to bottom: TO-3, TO-126, TO-92, SOT-23

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things.

Advantages :

The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are

1. Small size and minimal weight, allowing the development of miniaturized electronic devices.
2. Highly automated manufacturing processes, resulting in low per-unit cost.
3. Lower possible operating voltages, making transistors suitable for small, battery-powered applications.
4. No warm-up period for cathode heaters required after power application.
5. Lower power dissipation and generally greater energy efficiency.
6. Higher reliability and greater physical ruggedness.
7. Extremely long life. Some transistorized devices have been in service for more than 50 years.
8. Complementary devices available, facilitating the design of complementary-symmetry circuits, something not possible with vacuum tubes.
9. Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications.

EEE Short Questions and Answers (AC)

Fig : An AC Waveform

Author : Engr. Yousuf Ibrahim Khan

1. Define Cycle ?
ans : A portion of a waveform contained in one period of time.

2. What is Instantaneous value ?
ans : The magnitude of a waveform at any instant of time, denoted by lowercase letters.

3. What is a waveform ?
ans : The path traced by a quantity, plotted as a function of some variable such as positing, time, degrees, temperature, and so on.

4. What is an Alternating waveform ?
ans : A waveform that oscillates above and below a defined reference level.

5. What is a Periodic waveform and What is Phase relationship ?
ans : A waveform that continually repeats itself after a defined time interval. Phase relationship is an indication of which of two waveforms leads or lags the other, and by how many degrees or radians.

6. What is Peak to Peak Value ?
ans : The magnitude of the total swing of a signal from positive to negative peaks. The sum of the absolute values of the positive and negative peak values.

7. What is Peak Value ?
ans : The maximum value of waveform, denoted by uppercase letters.

8. What is Frequency (f) ?
ans :  The number of cycles of a periodic waveform that occur in 1 second.

9. What is Average value ?
ans : The level of a waveform defined by the condition that the area enclosed by the curve above this level is exactly equal to the area enclosed by the curve below this level.

10. What is Period (T) ?
ans : The time interval between successive repetitions of a periodic waveform.

EEE Short Questions and Answers (DC)

1. What is Superposition Theorem ?
ans : A network theorem that permits considering the effects of each source independently. The resulting current and/or voltage is the algebraic sum of the currents and/or voltages developed by each source independently.

2. Define Millman's Theorem ?
ans : A method employing source conversions that will permit the determination of unknown variables in a multi-loop network.

3. Define Maximum Power Transfer Theorem ?
ans : A theorem used to determine the load resistance necessary to ensure maximum power transfer to the load.

4. Define Norton's Theorem ?
ans : A theorem that permits the reduction of any two-terminal linear dc network to one having a single current source and parallel resistor.

5.  What is a Capacitor ?
ans : A fundamental electrical element having two conducting surfaces separated by an insulating material and having the capacity to store charge on its plate.

6. What is an Inductor ?
ans : A fundamental element of electrical systems constructed of numerous turns of wire around a ferromagnetic core or an air core.

7.  What is self-inductance (L) ?
ans : A measure of the ability of a coil to oppose any change in current trough the coil and to store energy in the form of a magnetic field in the region surrounding the coil.

8. Define Current Divider Rule (CDR) ?
ans : A method by which the current through parallel elements can be determined without first finding the voltage across those parallel elements.

9. What is an Open Circuit ?
ans : The absence of a direct connection between two points in a network.

10. What is a Short Circuit ?
ans : A direct connection of low resistive value that can significantly alter the behavior of an element or system.

How Programmable Logic Works ?

Fig : The Kemani is a low-cost CPLD rapid-prototyping kit perfect for breadboarding and prototyping applications. The Kemani features 26 pins of configurable I/O, both 3.3V and 5V tolerant. The Kemani also brings regulated power supply connections to the breadboard relieving the need for additional power circuitry. The on-board oscillator, selectable up to 220MHz, can be brought to the prototype via one of the I/O pins.

Published By : Michael Barr
Edited By : Engr. Yousuf Ibrahim Khan

In recent years, the line between hardware and software has blurred. Hardware now engineers create the bulk of their new digital circuitry in programming languages such as VHDL and Verilog. This article will help you make sense of programmable logic.

A quiet revolution is taking place. Over the past few years, the density of the average programmable logic device has begun to skyrocket. The maximum number of gates in an FPGA is currently around 500,000 and doubling every 18 months. Meanwhile, the price of these chips is dropping. What all of this means is that the price of an individual NAND or NOR is rapidly approaching zero! And the designers of embedded systems are taking note. Some system designers are buying processor cores and incorporating them into system-on-a-chip designs; others are eliminating the processor and software altogether, choosing an alternative hardware-only design. As this trend continues, it becomes more difficult to separate hardware from software. After all, both hardware and software designers are now describing logic in high-level terms, albeit in different languages, and downloading the compiled result to a piece of silicon. Surely no one would claim that language choice alone marks a real distinction between the two fields. Turing's notion of machine-level equivalence and the existence of language-to-language translators have long ago taught us all that that kind of reasoning is foolish. There are even now products that allow designers to create their hardware designs in traditional programming languages like C. So language differences alone are not enough of a distinction. Both hardware and software designs are compiled from a human-readable form into a machine-readable one. And both designs are ultimately loaded into some piece of silicon. Does it matter that one chip is a memory device and the other a piece of programmable logic? If not, how else can we distinguish hardware from software? I'm not convinced that an unambiguous distinction between hardware and software can ever be found, but I don't think that matters all that much. Regardless of where the line is drawn, there will continue to be engineers like you and me who cross the boundary in our work. So rather than try to nail down a precise boundary between hardware and software design, we must assume that there will be overlap in the two fields. And we must all learn about new things. Hardware designers must learn how to write better programs, and software developers must learn how to utilize programmable logic.
  
Types of programmable logic :

Many types of programmable logic are available. The current range of offerings includes everything from small devices capable of implementing only a handful of logic equations to huge FPGAs that can hold an entire processor core (plus peripherals!). In addition to this incredible difference in size there is also much variation in architecture. In this section, I'll introduce you to the most common types of programmable logic and highlight the most important features of each type.

PLDs :

At the low end of the spectrum are the original Programmable Logic Devices (PLDs). These were the first chips that could be used to implement a flexible digital logic design in hardware. In other words, you could remove a couple of the 7400-series TTL parts (ANDs, ORs, and NOTs) from your board and replace them with a single PLD. Other names you might encounter for this class of device are Programmable Logic Array (PLA), Programmable Array Logic (PAL), and Generic Array Logic (GAL). PLDs are often used for address decoding, where they have several clear advantages over the 7400-series TTL parts that they replaced. First, of course, is that one chip requires less board area, power, and wiring than several do. Another advantage is that the design inside the chip is flexible, so a change in the logic doesn't require any rewiring of the board. Rather, the decoding logic can be altered by simply replacing that one PLD with another part that has been programmed with the new design. Inside each PLD is a set of fully connected macrocells. These macrocells are typically comprised of some amount of combinatorial logic (AND and OR gates, for example) and a flip-flop. In other words, a small Boolean logic equation can be built within each macrocell. This equation will combine the state of some number of binary inputs into a binary output and, if necessary, store that output in the flip-flop until the next clock edge. Of course, the particulars of the available logic gates and flip-flops are specific to each manufacturer and product family. But the general idea is always the same. Because these chips are pretty small, they don't have much relevance to the remainder of this discussion. But you do need to understand the origin of programmable logic chips before we can go on to talk about the larger devices. Hardware designs for these simple PLDs are generally written in languages like ABEL or PALASM (the hardware equivalents of assembly) or drawn with the help of a schematic capture tool.

CPLDs :

As chip densities increased, it was natural for the PLD manufacturers to evolve their products into larger (logically, but not necessarily physically) parts called Complex Programmable Logic Devices (CPLDs). For most practical purposes, CPLDs can be thought of as multiple PLDs (plus some programmable interconnect) in a single chip. The larger size of a CPLD allows you to implement either more logic equations or a more complicated design. In fact, these chips are large enough to replace dozens of those pesky 7400-series parts.

Figure 1. Internal structure of a CPLD

Figure 1 contains a block diagram of a hypothetical CPLD. Each of the four logic blocks shown there is the equivalent of one PLD. However, in an actual CPLD there may be more (or less) than four logic blocks. I've just drawn it that way for simplicity. Note also that these logic blocks are themselves comprised of macrocells and interconnect wiring, just like an ordinary PLD.
Unlike the programmable interconnect within a PLD, the switch matrix within a CPLD may or may not be fully connected. In other words, some of the theoretically possible connections between logic block outputs and inputs may not actually be supported within a given CPLD. The effect of this is most often to make 100% utilization of the macrocells very difficult to achieve. Some hardware designs simply won't fit within a given CPLD, even though there are sufficient logic gates and flip-flops available. Because CPLDs can hold larger designs than PLDs, their potential uses are more varied. They are still sometimes used for simple applications like address decoding, but more often contain high-performance control-logic or complex finite state machines. At the high-end (in terms of numbers of gates), there is also a lot of overlap in potential applications with FPGAs. Traditionally, CPLDs have been chosen over FPGAs whenever high-performance logic is required. Because of its less flexible internal architecture, the delay through a CPLD (measured in nanoseconds) is more predictable and usually shorter.
  
FPGAs :

Fig 2: Internal structure of an FPGA

Field Programmable Gate Arrays (FPGAs) can be used to implement just about any hardware design. One common use is to prototype a lump of hardware that will eventually find its way into an ASIC. However, there is nothing to say that the FPGA can't remain in the final product. Whether or not it does will depend on the relative weights of development cost and production cost for a particular project. (It costs significantly more to develop an ASIC, but the cost per chip may be lower in the long run. The cost tradeoff involves expected number of chips to be produced and the expected likelihood of hardware bugs and/or changes. This makes for a rather complicated cost analysis, to say the least.). The development of the FPGA was distinct from the PLD/CPLD evolution just described. This is apparent when you look at the structures inside. Figure 2 illustrates a typical FPGA architecture. There are three key parts of its structure: logic blocks, interconnect, and I/O blocks. The I/O blocks form a ring around the outer edge of the part. Each of these provides individually selectable input, output, or bi-directional access to one of the general-purpose I/O pins on the exterior of the FPGA package. Inside the ring of I/O blocks lies a rectangular array of logic blocks. And connecting logic blocks to logic blocks and I/O blocks to logic blocks is the programmable interconnect wiring. The logic blocks within an FPGA can be as small and simple as the macrocells in a PLD (a so-called fine-grained architecture) or larger and more complex (coarse-grained). However, they are never as large as an entire PLD, as the logic blocks of a CPLD are. Remember that the logic blocks of a CPLD contain multiple macrocells. But the logic blocks in an FPGA are generally nothing more than a couple of logic gates or a look-up table and a flip-flop.
Because of all the extra flip-flops, the architecture of an FPGA is much more flexible than that of a CPLD. This makes FPGAs better in register-heavy and pipelined applications. They are also often used in place of a processor-plus-software solution, particularly where the processing of input data streams must be performed at a very fast pace. In addition, FPGAs are usually denser (more gates in a given area) and cost less than their CPLD cousins, so they are the de facto choice for larger logic designs.

Applications :

Now that you understand the technology, you're probably wondering what all of these FPGAs and CPLDs are doing within the embedded systems. However, their uses are so varied that it's impossible to generalize. Rather, I'll just touch on some of the emerging trends. This should hopefully answer your question, though admittedly indirectly.

Prototyping:

Many times a CPLD or FPGA will be used in a prototype system. A small device may be present to allow the designers to change a board's glue logic more easily during product development and testing. Or a large device may be included to allow prototyping of a system-on-a-chip design that will eventually find its way into an ASIC. Either way, the basic idea is the same: allow the hardware to be flexible during product development. When the product is ready to ship in large quantities, the programmable device will be replaced with a less expensive, though functionally equivalent, hard-wired alternative.

Embedded cores:

More and more vendors are selling or giving away their processors and peripherals in a form that is ready to be integrated into a programmable logic-based design. They either recognize the potential for growth in the system-on-a-chip area and want a piece of the royalties or want to promote the use of their particular FPGA or CPLD by providing libraries of ready-to-use building blocks. Either way, you will gain with lower system costs and faster time-to-market. Why develop your own hardware when you can buy an equivalent piece of virtual silicon?
The Intellectual Property (IP) market is growing rapidly. It's common to find microprocessors and microcontrollers for sale in this form, as well as complex peripherals like PCI controllers. Many of the IP cores are even configurable. Would you like a 16-bit bus or a 32-bit bus? Do you need the floating-point portion of the processor? And, of course, you'll find all of the usual supporting cast of simple peripherals like serial controllers and timer/counter units are available as well.

Hybrid chips :

There's also been some movement in the direction of hybrid chips, which combine a dedicated processor core with an area of programmable logic. The vendors of hybrid chips are betting that a processor core embedded within a programmable logic device will require far too many gates for typical applications. So they've created hybrid chips that are part fixed logic and part programmable logic. The fixed logic contains a fully functional processor and perhaps even some on-chip memory. This part of the chip also interfaces to dedicated address and data bus pins on the outside of the chip. Application-specific peripherals can be inserted into the programmable logic portion of the chip, either from a library of IP cores or the customer's own designs.

Reconfigurable computing:

As mentioned earlier, an SRAM-based programmable device can have its internal design altered on-the-fly. This practice is known as reconfigurable computing. Though originally proposed in the late 1960's by a researcher at UCLA, this is still a relatively new field of study. The decades-long delay had mostly to do with a lack of acceptable reconfigurable hardware. On-the-fly reprogrammable logic chips have only recently reached gate densities making them suitable for anything more than academic research. But the future of reconfigurable computing is bright and it is already finding a niche in high-end communications, military, and intelligence applications.

Application of Computational Intelligence in Motor Modeling

Citation : Yousuf Ibrahim Khan, Shahriar Rahman, Debasis Baishnab, Mohammed Moaz and S.M.Musfequr Rahman. Article: Application of Computational Intelligence in Motor Modeling. International Journal of Computer Applications 35(12):43-50, December 2011. Published by Foundation of Computer Science, New York, USA.

Abstract : Modeling is very important in the field of science and engineering. Modeling gives us an abstract and mathematical description of a particular system and describes its behavior. Once we get the model of a system then we can work with that in various applications without using the original system repeatedly. Computational Intelligence method like Artificial Neural Network is very sophisticated tool for modeling and data fitting problems. Modeling of Electrical motors can also be done using ANN. The Neural network that will represent the model of the motor will be a useful tool for future use especially in digital control systems. The parallel structure of a neural network makes it potentially fast for the computation of certain tasks. The same feature makes a neural network well suited for implementation in VLSI technology. Hardware realization of a Neural Network (NN), to a large extent depends on the efficient implementation of a single neuron. In this paper only a motor model is presented along with some neural networks those will mimic the motor behavior acquiring data from the original motor output. 

To access the Full Paper, Please visit : 

http://www.ijcaonline.org/archives/volume35/number12/4556-6443

Artificial Neural Network based Short Term Load Forecasting of Power System

Citation : Salman Quaiyum, Yousuf Ibrahim Khan, Saidur Rahman and Parijat Barman. Article: Artificial Neural Network based Short Term Load Forecasting of Power System. International Journal of Computer Applications 30(4):1-7, September 2011. Published by Foundation of Computer Science, New York, USA

Abstract : Load forecasting is the prediction of future loads of a power system. It is an important component for power system energy management. Precise load forecasting helps to make unit commitment decisions, reduce spinning reserve capacity and schedule device maintenance plan properly. Besides playing a key role in reducing the generation cost, it is also essential to the reliability of power systems. By forecasting, experts can have an idea of the loads in the future and accordingly can make vital decisions for the system. This work presents a study of short-term hourly load forecasting using different types of Artificial Neural Networks.

For Full access of this paper, please visit :

http://www.ijcaonline.org/archives/volume30/number4/3633-5073

Thyratron

Fig 1: R.C.A. brand 885 Triode Thyratron

A thyratron is a type of gas filled tube used as a high energy electrical switch and controlled rectifier. Triode, tetrode and pentode variations of the thyratron have been manufactured in the past, though most are of the triode design. Because of the gas fill, thyratrons can handle much greater currents than similar hard vacuum valves/tubes since the positive ions carry considerable current. Gases used include mercury vapor, xenon, neon, and (in special high-voltage applications or applications requiring very short switching times) hydrogen. Unlike a vacuum tube, a thyratron cannot be used to amplify signals linearly. In the 1920s Thyratrons were derived from early vacuum tubes such as the UV-200, which contained a small amount of argon gas to increase its sensitivity as a radio signal detector; and the German LRS Relay tube, which also contained argon gas. Gas rectifiers which predated vacuum tubes, such as the argon-filled General Electric "Tungar bulb" and the Cooper-Hewitt mercury pool rectifier, also provided an influence. A thyratron is basically a "controlled gas rectifier". Irving Langmuir and G. S. Meikle of GE are usually cited as the first investigators to study controlled rectification in gas tubes, about 1914. The first commercial thyratrons didn't appear until around 1928. A solid-state device with similar operating characteristics is the silicon controlled rectifier (SCR).

Construction : A typical hot-cathode thyratron uses a heated filament cathode, completely contained within a shield assembly with a control grid on one open side, which faces the plate-shaped anode. When positive voltage is applied to the anode, if the control electrode is kept at cathode potential, no current flows. When the control electrode is made slightly positive, gas between the anode and cathode ionizes and conducts current. The shield prevents ionized current paths that might form within other parts of the tube. The gas in a thyratron is typically at a fraction of the pressure of air at sea level; 15 to 30 millibars (1.5 to 3 kPa) is typical. Both hot-and cold-cathode versions are encountered. A hot cathode is at an advantage, as ionization of the gas is made easier; thus, the tube's control electrode is more sensitive. Once turned on, the thyratron will remain on (conducting) as long as there is a significant current flowing through it. When the anode voltage or current falls to zero, the device switches off.

 Fig 2: Rare Z806W relay tube used in elevators

Applications : Small thyratrons were manufactured in the past for controlling electromechanical relays and for industrial applications such as motor and arc-welding controllers. Large thyratrons are still manufactured, and are capable of operation up to tens of kiloamperes (kA) and tens of kilovolts (kV).

Modern applications include pulse drivers for pulsed radar equipment, high-energy gas lasers, radiotherapy devices, particle accelerators and in Tesla coils and similar devices. Thyratrons are also used in high-power UHF television transmitters, to protect inductive output tubes from internal shorts, by grounding the incoming high-voltage supply during the time it takes for a circuit breaker to open and reactive components to drain their stored charges. This is commonly called a "crowbar" circuit.

Fig 3: Giant GE hydrogen thyratron, used in pulsed radars, next to miniature 2D21 thyratron used to trigger relays in jukeboxes

Thyratrons have been replaced in most low and medium-power applications by corresponding semiconductor devices known as thyristors (sometimes called silicon-controlled rectifiers, or SCRs) and triacs. However, switching service requiring voltages above 20 kV and involving very short risetimes remains within the domain of the thyratron. Variations of the thyratron idea are the krytron, the sprytron, the ignitron, and the triggered spark gap, all still used today in special applications.

One miniature thyratron, the triode 6D4, found an additional use as a potent noise source, when operated as a diode in a transverse magnetic field. Sufficiently filtered for "flatness" ("white noise") in a band width of interest, such noise was used for testing radio receivers, servo systems and occasionally in analog computing as a random value source.

The 885 is a small thyratron tube, using xenon gas. This device was used extensively in the timebase circuits of early oscilloscopes in the 1930s. It was employed in a circuit called a relaxation oscillator. During World War II small thyratrons, similar to the 885 were utilized in pairs to construct bistables, the "memory" cells used by early computers and code breaking machines. Thyratrons were also used for phase angle control of alternating current (AC) power sources in battery chargers and light dimmers, but these were usually of a larger current handling capacity than the 885. The 885 is electrically identical to the 884/6Q5, which uses an octal base.

EEE Short Questions and Answers

 

Fig 1 : An Engineer is taking values using a Multimeter 

1. What is a Controller ?
ans : Any device that serves to control the power to the equipment to which it is connected.

2. What is an Induction Motor ?
ans : An ac motor in which the stator or primary winding is connected to the power source and a secondary winding carries the induced current.

3. What is Mesh Analysis ?

ans : An algebraic technique for writing simultaneous linear equations in terms of unknown mesh currents in any electrical network.

4. What is Phase sequence ?
ans : The order in which successive phase (or line) voltages reach their respective maximum values.

5. What do you mean by HSGT and HSST ?
ans : An acronym for high speed ground transport and high speed surface transport.

6. What is a Brushless DC motor ?
ans : A small dc motor in which commutation is produced by electronic means using a variety of ingenious engineering designs.

7. What is a Transducer ?
ans : An energy conversion device that receives energy from one source and delivers energy to another system in such a manner that the desired characteristics of the input appear at the output.

8. What is a Short circuit test ?
ans : A test to determine the equivalent primary and secondary copper losses of the transformer, along with its equivalent resistance, reactance, and impedance. Data from this test enables calculation of voltage regulation.

9. What is an Autotransformer ?
ans : Multi winding transformer connected in such a way that it has one continuous winding of which part is common to both the primary and secondary circuits to which the auto-transformer is connected.

10. What is a Transformer ?
ans : A device which operates on the principal of mutual induction and used for transferring energy from one circuit to another.

Tracking Dragonflies on the Wing

Fig 1: Duke University researcher Matt Reynolds and colleagues have developed a sensor and transmitter light enough to be carried by a dragonfly, transmitting the insect's nerve impulses to researchers at 5 megabits per second as it hunts its prey on the wing.
(Credit: Duke University)

Research Published : Nov 14, 2011

Duke University electrical engineers have developed a wirelessly powered telemetry system that is light and powerful enough to allow scientists to study the intricate neurological activity of dragonflies as they capture prey on the wing.

Past studies of insect behavior have been limited by the fact that today's remote data collection, or telemetry, systems are too heavy to allow the insects to act naturally, as they would in the wild. The new system uses no batteries, but rather beams power wirelessly to the flying dragonfly.

Duke electrical engineer Matt Reynolds, working with Reid Harrison at Intan Technologies, developed the chip for scientists at the Howard Hughes Medical Institute (HHMI), who are trying to better understand the complex flight control system of dragonflies. They gather their information by attaching tiny electrodes to individual nerve cells in the dragonfly’s nerve cord and recording the electrical activity of the dragonfly's neurons and muscles. Existing systems for recording neural activity require large batteries that are far too heavy to be carried by a dragonfly, so experiments to date have been carried out with immobilized dragonflies.

If the new system proves successful, the researchers expect that broad new avenues into studying behavior of small animals remotely will become available for the first time.

“We developed a wireless power system that avoids the need altogether for the size and weight of a battery,” said Reynolds, assistant professor of electrical and computer engineering at Duke’s Pratt School of Engineering. He presented the results of his work today at the annual Biomedical Circuits and Systems Conference, held by the Institute of Electrical and Electronics Engineers (IEEE) in San Diego.

“The system provides enough power to the chip attached to a flying dragonfly that it can transmit in real time the electrical signals from many dragonfly neurons,” Reynolds said.

The chip receives power wirelessly from a transmitter within the flight arena in which the experiments are carried out. The system can send enough power to the chip to enable it to send back reams of data at over five megabits per second, which is comparable to a typical home internet connection. This is important, the scientists said, because they plan to sync the neuronal data gathered from the chip with high-speed video taken while the insect is in flight and preying on fruit flies.

“Capturing this kind of data in the past has been exceedingly challenging,” said Anthony Leonardo, a neuroscientist who studies the neural basis of insect behavior at HHMI’s Janelia Farm Research Campus in Virginia. “In past studies of insect neurons the animal is alert, but restrained, and observing scenarios on a projection screen. A huge goal for a lot of researchers has been to get data from live animals who are acting naturally.”

The average weight of the dragonfly species involved in these studies is about 400 milligrams, and Leonardo estimates that an individual dragonfly can carry about one-third of its weight without negatively impacting its ability to fly and hunt. Currently, most multi-channel wireless telemetry systems weigh between 75 and 150 times more than a dragonfly, not counting the weight of the battery, which rules them out for most insect studies, he said. A battery-powered version of the insect telemetry system, previously developed by Harrison and Leonardo, weighs 130 milligrams -- liftable by a foraging dragonfly but with difficulty.

The weight of the chip that Reynolds and his team developed is just 38 milligrams, or less than half of a typical postage stamp. It is also one-fifth the weight and has 15 times greater bandwidth of the previous generation system, Reynolds said.

The researchers expect to begin flight experiments with dragonflies over the next few months. The testing will take place in a specially designed flight arena at HHMI's Janelia Farm complex equipped with nature scenes on the walls, a pond and plenty of fruit flies for the dragonflies to eat.

The chip, with two hair-thin antennae projecting from the back, will be attached to the belly of the insect so as not to interfere with the wings. Since the chip must have uninterrupted radio contact with the power transmitter on the ground, the chip is carried much like the backup parachute on the underside of the animal.

The project is supported in part by HHMI. Duke graduate student Stewart Thomas was also a member of the team.

Department of Electrical & Computer Engineering : Duke University

Fig 1: ECE student at Duke is working with an Oscilloscope (Tektronix TDS 3000 series)

Research areas in Duke University : (Department of Electrical and Computer Engineering)

Research areas:  

Architecture and Networking : Research in computer architecture and networking focuses on architecting next generation computer systems that will be high-performance, reliable, self-healing, and even self assembled. Furthermore, we are networking these computers over the wired and wireless media to realize a future in which information will be available anytime, anywhere.  

Biological Applications : Faculty in this research subgroup collaborate with other ECE faculty, and with faculty in other departments and in the medical school, to address a wide variety of applications of electrical and computer engineering to biological problems.  

Circuits and Systems : This research focuses on the behavior, integration and testing of components in both digital and analog circuits and systems. We leverage the properties of emerging technologies to deliver new capabilities in mixed-signal, RF, and digital applications and in many cases seek to exploit new phenomena at the nanoscale.  

Nanosystems, Devices & Materials : This research focuses on devices and systems that exploit the properties of materials at the nanoscale. An important aspect of this work is to study the broad, vertical implications of the behavior of materials on integrated systems in new application domains.  

Quantum Computing & Photonics :  Adequate utilization of light promises unparalleled performance in a wide range of applications in imaging, sensing, energy sciences and advanced information processing. The Quantum Computing & Photonics (or, the appropriate research group name here) research activities at Duke explore novel approaches to building unique optical devices and systems leveraging advances in new material systems, nano-and micro-fabrication technologies, integrated microsystems concepts and computational techniques. 

Sensing & Signals : The sensing and signals group focuses on fundamental theoretical and methodological aspects of information processing with a wide variety of important and exciting applications. Recording and analyzing signals, images, and electromagnetic waves is a key component of Duke's interdisciplinary research in ECE. The researchers in this area tackle challenging problems ranging from the measurement of lightening to improving hearing with cochlear implants and from homeland security to the next generation of digital cameras. 

Waves & Metamaterials : The next generation of materials will be engineered with desirable properties, depending on the need of an application. When an object needs to be invisible, it can be developed from a material with negative refractive index. Revolutionary research from the waves and metamaterial labs makes Duke an exciting place to be in.

For more information, please visit : http://www.ece.duke.edu/

Pulse Forming Network

Figure 1 : A pulse forming network for a laser rangefinder

A Pulse Forming Network (PFN) accumulates electrical energy over a comparatively long time, then releases the stored energy in the form of a relatively square pulse of comparatively short duration for various pulsed power applications. In practice, a PFN is charged by means of a high voltage power source, then rapidly discharged into a load via a high voltage switch, such as a spark gap or hydrogen thyratron. The load may be a high power microwave oscillator such as a klystron or magnetron, a flashtube, or even an electromagnet. Depending upon the application, the output pulse repetition rate may range from a fraction of a Hertz to over 10kHz.

Implementation :

A PFN consists of a series of high voltage energy storage capacitors and inductors. These components are interconnected (as a "ladder network") that behaves similarly to a length of transmission line. For this reason, a PFN is sometimes called an "artificial, or synthetic, transmission line". Electrical energy is initially stored within the charged capacitors of the PFN. Sometimes an actual length of transmission line is used as the pulse forming network. This can give substantially flat topped pulses at the inconvenience of using of a large length of cable. A Blumlein transmission line is a particular configuration of transmission lines used to create high-voltage pulses with short rise and fall times. Its principle is closely related to a pulse-forming transmission line discharge, although a Blumlein's output voltage is the same as the charging voltage whereas the Pulse-forming transmission line outputs half the charging voltage.

Application of PFN :

Upon command, a high voltage switch transfers the energy stored within the PFN into the load. When the switch "fires" (closes), the network of capacitors and inductors within the PFN creates an approximately square output pulse of short duration and high power. This high power pulse becomes a brief source of high power to the load. Sometimes a specially designed pulse transformer is connected between the PFN and load. This technique improves the impedance match between the PFN and the load so as to improve power transfer efficiency. A pulse transformer is typically required when driving higher impedance devices such as klystrons or magnetrons from a PFN. Because the PFN is charged over a relatively long time and then discharged over a very short time, the output pulse may have a peak power of megawatts or even terawatts. The combination of high voltage source, PFN, HV switch, and pulse transformer (when required) is sometimes called a "power modulator" or "pulser".