Read the text: Analogue electronics  

Read the text: Analogue electronics

Передмова

Метою “Методичних вказiвок” є формування впродовж 72 годин аудиторних занять у студентів (вхідний рівень володіння мовою – В1) вмiнь та навичок читання за тематикою спеціальності 6.050802 “ Радіотехніка та телекомунікаційні системи” на ІІ курсі навчання Інституту радіоелектроніки і телекомунікацій (вихідний рівень володіння мовою – В2). За рахунок тренування і виконання читання текстів і завдань студенти зможуть вільно читати оригінальну літературу іноземною мовою у відповідній галузі знань, оформляти витягнуту з іноземних джерел інформацію у вигляді перекладу або резюме.

Кожний урок складається з тексту й післятекстових вправ, які розраховані на удосконалення навичок читання, активізацію словарного і граматичного мінімуму професійно-орієнтованого тексту.

“Методичні вказiвки” спрямовані на викладання відбору змістової інформації із спеціальних англомовних текстів, передбачено вимогами Програми вивчення іноземних мов у нефілологічному ВУЗі.

Lesson 1

Read the text: Analogue electronics

Analogue electronics (or analog in American English) are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two different levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal. The word analogue is derived from the Greek word ανάλογος (analogos) meaning "proportional".

An analogue signal uses some attributes of the medium to convey the signal's information. Electrical signals represent information by changing their voltage, current, frequency, or total charge. Information is converted from some other physical forms (such as sound, light, temperature, pressure, position) to an electrical signal by a transducer which converts one type of energy into another (e.g. a microphone).

The signals take any value from a given range, and each unique signal value represents different information. Any change in the signal is meaningful, and each level of the signal represents a different level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one volt representing one degree Celsius. In such a system 10 volts would represent 10 degrees, and 10.1 volts would represent 10.1 degrees.



Another method of conveying an analogue signal is to use modulation. In this, a base carrier signal has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency. Other techniques, such as phase modulation or changing the phase of the carrier signal, are also used.

In an analogue sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape.

Analogue systems invariably include noise; that is, random disturbances or variations, some caused by the random thermal vibrations of atomic particles. Since all variations of an analogue signal are significant, any disturbance is equivalent to a change in the original signal and so appears as noise. As the signal is copied and re-copied, or transmitted over long distances, these random variations become more significant and lead to signal degradation. Other sources of noise may include external electrical signals or poorly designed components. These disturbances are reduced by shielding, and using low-noise amplifiers (LNA).

Since the information is encoded differently in analogue and digital electronics, the way they process a signal is consequently different. All operations that can be performed on an analogue signal such as amplification, filtering, limiting, and others, can also be duplicated in the digital domain. Every digital circuit is also an analogue circuit, in that the behaviour of any digital circuit can be explained using the rules of analogue circuits.



The first electronic devices invented and mass produced were analogue. The use of microelectronics has reduced the cost of digital techniques and now makes digital methods feasible and cost-effective such as in the field of human-machine communication by voice.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 2

Read the text: Signal generators (1)

Signal generators, also known variously as function generators, RF(radio frequency)and microwave signal generators, pitch generators, arbitrary waveform generators, digital pattern generators or frequency generators are electronic devices that generate repeating or non-repeating electronic signals (in either the analog or digital domains). They are generally used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices; though they often have artistic uses as well.

A function generator produces simple repetitive waveforms. Such devices contain an electronic oscillator, a circuit that is capable of creating a repetitive waveform. (Modern devices may use digital signal processing to synthesize waveforms, followed by a digital to analog converter, or DAC, to produce an analog output). The most common waveform is a sine wave, but saw tooth, step (pulse), square, and triangular waveform oscillators are commonly available as are arbitrary waveform generators (AWGs). If the oscillator operates above the audio frequency range (>20 kHz), the generator will often include some sort of modulation function such as amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM) as well as a second oscillator that provides an audio frequency modulation waveform.

Function generators are typically used in simple electronics repair and design; where they are used to stimulate a circuit under test. A device such as an oscilloscope is then used to measure the circuit's output. Function generators vary in the number of outputs they feature, frequency range, frequency accuracy and stability, and several other parameters.

Arbitrary waveform generators, or AWGs, are sophisticated signal generators which allow the user to generate arbitrary waveforms, within published limits of frequency range, accuracy, and output level. Unlike function generators, which are limited to a simple set of waveforms, an AWG allows the user to specify a source waveform in a variety of different ways. AWGs are generally more expensive than function generators, and are often more highly limited in available bandwidth; as a result, they are generally limited to higher-end design and test applications.

RF (radio frequency) and microwave signal generators are used for testing components, receivers and test systems in a wide variety of applications including cellular communications, WiFi, WiMAX, GPS, audio and video broadcasting, satellite communications, radar and electronic warfare. RF and microwave signal generators normally have similar features and capabilities, but are differentiated by frequency range. RF signal generators typically range from a few kHz to 6 GHz, while microwave signal generators cover a much wider frequency range, from less than 1 MHz to at least 20 GHz. Some models go as high as 70 GHz with a direct coaxial output, and up to hundreds of GHz when used with external waveguide source modules. RF and microwave signal generators can be classified further as analog or vector signal generators.

Analog Signal Generators are capable of producing CW (continuous wave) tones. The output frequency can be tuned anywhere over their entire frequency range. In addition, many models offer various types of analog modulation, either as standard equipment or as an optional capability to the base unit. This could include AM, FM, phase modulation and pulse modulation. Another common feature is a built-in attenuator which makes it possible to vary the signal’s output power. Depending on the manufacturer and model, output powers can range from -135 to +30 dBm. A wide range of output power is desirable, since different applications require different amounts of signal power.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 3

Read the text: Signal generators (2)

With the advent of digital communications systems, it is no longer possible to adequately test these systems with traditional analog signal generators. This has led to the development of vector signal generators, also known as digital signal generators. These signal generators are capable of generating digitally-modulated radio signals that may use any of a large number of digital modulation formats.

Also known as 'data pattern generator' or more often 'digital pattern generator', this type of signal generators produces logic types of signals - that is logic 1's and 0's in the form of conventional voltage levels. The usual voltage standards are: LVTTL, LVCMOS. As such, they must be distinguished from 'pulse/pattern generators', which refers to signal generators able to generate logic pulses with different analog characteristics (such as pulse rise/fall time, high level length).

Logic signal generators (digital pattern generators) are used as stimulus source for digital integrated circuits and embedded systems - for functional validation and testing.

There are several classes of signal generators designed for specific applications. A pitch generator is a type of signal generator optimized for use in audio and acoustics applications. Pitch generators typically include sine waves over the audio frequency range (20 Hz–20 kHz). Sophisticated pitch generators will also include sweep generators (a function which varies the output frequency over a range, in order to make frequency-domain measurements), multipitch generators (which output several pitches simultaneously, and are used to check for intermodulation distortion and other non-linear effects), and tone bursts (used to measure response to transients). Pitch generators are typically used in conjunction with sound level meters, when measuring the acoustics of a room or a sound reproduction system, and/or with oscilloscopes or specialized audio analyzers.

A video signal generator is a device which outputs predetermined video and/or television waveforms, and other signals used to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain synchronization signals appropriate for television, including horizontal and vertical sync pulses (in analog) or sync words (in digital). Generators of composite video signals will also include a colorburst signal as part of the output. Video signal generators are available for a wide variety of applications, and for a wide variety of digital formats; many of these also include audio generation capability (as the audio track is an important part of any video or television program or motion picture).

New high-speed DACs provide up to 16-bit resolution at sample rates in excess of 1 GS/s. These devices provide the foundation for an AWG with the bandwidth and dynamic range to address modern radio and communication applications. In combination with a quadrature modulator and advanced digital signal processing, high-speed DACs can be applied to create a full-featured vector signal generator with very high modulation bandwidth. Example applications include commercial wireless standards such as Wi-Fi (IEEE 802.11), WiMAX (IEEE 802.16) and LTE, in addition to military standards such as those specified in the Joint Tactical Radio System (JTRS) initiative. Also, broad modulation bandwidth allows multi-carrier signal generation, necessary for testing receiver adjacent channel rejection.

1. Write down the key-words that help you to catch the main idea of the text.

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 4

Read the text: Adaptive Filtering System Configurations

There are four major types of adaptive filtering configurations; adaptive system identification, adaptive noise cancellation, adaptive linear prediction, and adaptive inverse system. All of the above systems are similar in the implementation of the algorithm, but different in system configuration.

The adaptive system identification is primarily responsible for determining a discrete estimation of the transfer function for an unknown digital or analog system. The same input is applied to both the adaptive filter and the unknown system from which the outputs are compared. The output of the adaptive filter is subtracted from the output of the unknown system resulting in a desired signal . The resulting difference is an error signal used to manipulate the filter coefficients of the adaptive system trending towards an error signal of zero.

After a number of iterations of this process are performed, and if the system is designed correctly, the adaptive filter’s transfer function will converge to, or near to, the unknown system’s transfer function. For this configuration, the error signal does not have to go to zero, although convergence to zero is the ideal situation, to closely approximate the given system. There will, however, be a difference between adaptive filter transfer function and the unknown system transfer function if the error is nonzero and the magnitude of that difference will be directly related to the magnitude of the error signal. Additionally the order of the adaptive system will affect the smallest error that the system can obtain. If there are insufficient coefficients in the adaptive system to model the unknown system, it is said to be under specified. This condition may cause the error to converge to a nonzero constant instead of zero. In contrast, if the adaptive filter is over specified, meaning that there are more coefficients than needed to model the unknown system, the error will converge to zero, but it will increase the time it takes for the filter to converge.

The second configuration is the adaptive noise cancellation configuration. In this configuration the input, a noise source, is compared with a desired signal, which consists of a signal corrupted by another noise. The adaptive filter coefficients adapt to cause the error signal to be a noiseless version of the signal. Both of the noise signals for this configuration need to be uncorrelated to the signal. In addition, the noise sources must be correlated to each other in some way, preferably equal, to get the best results.

Adaptive linear prediction is the third type of adaptive configuration. This configuration essentially performs two operations. The first operation, if the output is taken from the error signal, is linear prediction. The adaptive filter coefficients are being trained to predict, from the statistics of the input signal, what the next input signal will be. The second operation, if the output is taken from, is a noise filter similar to the adaptive noise cancellation.

Neither the linear prediction output nor the noise cancellation output will converge to an error of zero. This is true for the linear prediction output because if the error signal did converge to zero, this would mean that the input signal is entirely deterministic, in which case we would not need to transmit any information at all. In the case of the noise filtering output, as outlined in the previous section, will converge to the noiseless version of the input signal.

The final filter configuration is the adaptive inverse system configuration. The goal of the adaptive filter here is to model the inverse of the unknown system. This is particularly useful in adaptive equalization where the goal of the filter is to eliminate any spectral changes that are caused by a prior system or transmission line. The way this filter works is as follows. The input is sent through the unknown filter and then through the adaptive filter resulting in an output. The input is also sent through a delay to attain. As the error signal is converging to zero, the adaptive filter coefficients are converging to the inverse of the unknown system. For this configuration, as for the system identification configuration, the error can theoretically go to zero. This will only be true, however, if the unknown system consists only of a finite number of poles or the adaptive filter is an IIR filter. If neither of these conditions is true, the system will converge only to a constant due to the limited number of zeroes available in an FIR system.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 5

Read the text: Performance Measures in Adaptive Systems

Six performance measures will be discussed in the following section: convergence rate, minimum mean square error, computational complexity, stability, robustness, and filter length. The convergence rate determines the rate at which the filter converges to its resultant state. Usually a faster convergence rate is a desired characteristic of an adaptive system. Convergence rate is not, however, independent of all of the other performance characteristics. There will be a tradeoff, in other performance criteria, for an improved convergence rate and there will be a decreased convergence performance for an increase in other performance. For example, if the convergence rate is increased, the stability characteristics will decrease, making the system more likely to diverge instead of converge to the proper solution. Likewise, a decrease in convergence rate can cause the system to become more stable. This shows that the convergence rate can only be considered in relation to the other performance metrics, not by itself with no regards to the rest of the system.

The minimum mean square error (MSE) is a metric indicating how well a system can adapt to a given solution. A small minimum MSE is an indication that the adaptive system has accurately modeled, predicted, adapted and/or converged to a solution for the system. A very large MSE usually indicates that the adaptive filter cannot accurately model the given system or the initial state of the adaptive filter is an inadequate starting point to cause the adaptive filter to converge. There are a number of factors which will help to determine the minimum MSE including, but not limited to; quantization noise, order of the adaptive system, measurement noise, and error of the gradient due to the finite step size.

Computational complexity is particularly important in real time adaptive filter applications. When a real time system is being implemented, there are hardware limitations that may affect the performance of the system. A highly complex algorithm will require much greater hardware resources than a simplistic algorithm.

Stability is probably the most important performance measure for the adaptive system. By the nature of the adaptive system, there are very few completely asymptotically stable systems that can be realized. In most cases the systems that are implemented are marginally stable, with the stability determined by the initial conditions, transfer function of the system and the step size of the input.

The robustness of a system is directly related to the stability of a system. Robustness is a measure of how well the system can resist both input and quantization noise.

The filter length of the adaptive system is inherently tied to many of the other performance measures. The length of the filter specifies how accurately a given system can be modeled by the adaptive filter. In addition, the filter length affects the convergence rate, by increasing or decreasing computation time, it can affect the stability of the system, at certain step sizes, and it affects the minimum MSE. If the filter length of the system is increased, the number of computations will increase, decreasing the maximum convergence rate. Conversely, if the filter length is decreased, the number of computations will decrease, increasing the maximum convergence rate. For stability, due to an increase in length of the filter for a given system, you may add additional poles or zeroes that may be smaller than those that already exist. In this case the maximum step size, or maximum convergence rate, will have to be decreased to maintain stability. Finally, if the system is under specified, meaning there are not enough pole and/or zeroes to model the system, the mean square error will converge to a nonzero constant. If the system is over specified, meaning it has too many poles and/or zeroes for the system model, it will have the potential to converge to zero, but increased calculations will affect the maximum convergence rate possible.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 6

Read the text: Radio transmitters

In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves. In addition to their use in broadcasting, transmitters are necessary component parts of many electronic devices that communicate by radio, such as cell phones, wireless computer networks, Bluetooth enabled devices, two-way radios in aircraft, ships, and spacecraft, radar sets, and navigational beacons. The term transmitter is usually limited to equipment that generates radio waves for communication purposes; or radiolocation, such as radar and navigational transmitters.

The term is used more specifically to refer to transmitting equipment used for broadcasting, as in radio transmitter or television transmitter. This usage usually includes both the transmitter proper as described above, and the antenna, and often the building it is housed in.

An unrelated use of the term is in industrial process control, where a "transmitter" is a telemetry device which converts measurements from a sensor into a signal, and sends it, usually via wires, to be received by some display or control device located a distance away.

A transmitter can be a separate piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and receiver combined in one unit is called a transceiver. The term transmitter is often abbreviated "XMTR" or "TX" in technical documents. The purpose of most transmitters is radio communication of information over a distance. The information is provided to the transmitter in the form of an electronic signal, such as an audio (sound) signal from a microphone, a video (TV) signal from a TV camera, or in wireless networking devices a digital signal from a computer. The transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is often called the carrier. This process is called modulation. The information can be added to the carrier in several different ways, in different types of transmitter. In an amplitude modulation (AM) transmitter, the information is added to the radio signal by varying its amplitude (strength). In a frequency modulation (FM) transmitter, it is added by varying the radio signal's frequency slightly. Many other types of modulation are used.

The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as cell phones, walkie-talkies, and auto keyless remotes, or for more powerful transmitters may be located on top of a building or on a separate tower, and connected to the transmitter by a feed line (transmission line).

A radio transmitter is an electronic circuit which transforms electric power from a battery or electrical mains into a radio frequency alternating current, which reverses direction millions to billions of times per second. The energy in such a rapidly-reversing current can radiate off a conductor (the antenna) as electromagnetic waves (radio waves). The transmitter also "piggybacks" information, such as an audio or video signal, onto the radio frequency current to be carried by the radio waves. When they strike the antenna of a radio receiver, the waves excite similar (but less powerful) radio frequency currents in it. The radio receiver extracts the information from the received waves.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 7

Read the text: Radio receiver dynamic range

Sensitivity is one of the main specifications of any radio receiver. However the sensitivity of a set is by no means the whole story. The specification for a set may show it to have an exceedingly good level of sensitivity, but when it is connected to an antenna its performance may be very disappointing because it is easily overloaded when strong signals are present, and this may impair its ability to receive weak signals. In today's radio communications environment where there are very many transmitters close by and further away, good levels of sensitivity are needed along with the ability to handle strong signals both on and off channel and the dynamic range of the radio receiver is very important.

The overall dynamic range of the receiver is very important because it is just as important for a set to be able to handle strong signals well as it is to be able to pick up weak ones. This becomes very important when trying to pick up weak signals in the presence of nearby strong ones. Under these circumstances a set with a poor dynamic range may not be able to hear the weak stations picked up by a less sensitive set with a better dynamic range. Problems like blocking, inter-modulation distortion and the like within the receiver may mask out the weak signals, despite the set having a very good level of sensitivity. These parameters are obviously important when determining what equipment should be used in a radio communications system.

The dynamic range of a radio receiver is essentially the range of signal levels over which it can operate. The low end of the range is governed by its sensitivity whilst at the high end it is governed by its overload or strong signal handling performance. Specifications generally use figures based on either the inter-modulation performance or the blocking performance. Unfortunately it is not always possible to compare one set with another because dynamic range like many other parameters can be quoted in a number of ways. However to gain an idea of exactly what the dynamic range of a radio receiver means it is worth looking at the ways in which the measurements are made to determine the range of the radio receiver.

The first specification to investigate is the sensitivity of a set. The main limiting factor in any radio receiver is the noise generated. For most applications either the signal to noise ratio or the noise figure is used as described in a previous issue of MT. However for dynamic range specifications a figure called the minimum discernible signal (MDS) is often used. This is normally taken as a signal equal in strength to the noise level. As the noise level is dependent upon the bandwidth used, this also has to be mentioned in the specification. Normally the level of the level of the MDS is given in dBm i.e. dB relative to a milliwatt and typical values are around -135 dBm in a 3 kHz bandwidth.

Although the sensitivity is important the way in which a radio receiver handles strong signals is also very important. Here the overload performance governs how well the receiver performance. In the ideal world the output of an RF amplifier would be proportional to the input for all signal levels. However RF amplifiers only have a limited output capability and it is found that beyond a certain level the output falls below the required level because it cannot handle the large levels required of it.

The fact that the RF amplifier is non-linear does not create a major problem in itself. However the side effects do. When a signal is passed through a non-linear element there are two main effects which are noticed. The first is that harmonics are generated. Fortunately these are unlikely to cause a major problem. For a harmonic to fall near the frequency being received, a signal at half the received frequency must enter the RF amplifier. The front end tuning should reduce this by a sufficient degree for it not to be a noticeable problem under most circumstances.

Another problem that can occur when a strong signal is present is known as blocking. As the name implies it is possible for a strong signal to block or at least reduce the sensitivity of a radio receiver. The effect can be noticed when listening to a relatively weak station and a nearby transmitter starts to radiate, and the wanted signal reduces in strength. The effect is caused when the front-end RF amplifier starts to run into compression. When this occurs the strongest signal tends to "capture" the RF amplifier reducing the strength of the other signals. The effect is the same as the capture effect associated with FM signals.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 8

Read the text: Amplifiers

When people refer to "amplifiers," they're usually talking about stereo components or musical equipment. But this is only a small representation of the spectrum of audio amplifiers. There are actually amplifiers all around us. You'll find them in televisions, computers, portable CD players and most other devices that use a speaker to produce sound.

Sound is a fascinating phenomenon. When something vibrates in the atmosphere, it moves the air particles around it. Those air particles in turn move the air particles around them, carrying the pulse of the vibration through the air. Our ears pick up these fluctuations in air pressure and translate them into electrical signals the brain can process.

Electronic sound equipment works the same basic way. It represents sound as a varying electric current. Broadly speaking, there are three steps in this sort of sound reproduction:

· A player (such as a tape deck) re-interprets this pattern as an electrical signal and uses this electricity to move a speaker cone back and forth. This re-creates the air-pressure fluctuations originally recorded by the microphone.

All the major components in this system are essentially translators: They take the signal in one form and put it into another. In the end, the sound signal is translated back into its original form, a physical sound wave.

­ In order to register all of the minute pressure fluctuations in a sound wave, the microphone diaphragm has to be extremely sensitive. This means it is very thin and moves only a short distance. Consequently, the microphone produces a fairly small electrical current.

This is fine for most of the stages in the process - it's strong enough for use in the recorder, for example, and it is easily transmitted through wires. But the final step in the process -- pushing the speaker cone back and forth -- is more difficult. To do this, it is necessary to boost the audio signal so it has a larger current while preserving the same pattern of charge fluctuation.

In actuality, the amplifier generates a completely new output signal based on the input signal. These signals may be considered as two separate circuits. The output circuit is generated by the amplifier's power supply, which draws energy from a battery or power outlet. If the amplifier is powered by household alternating current, where the flow of charge changes directions, the power supply will convert it into direct current, where the charge always flows in the same direction. The power supply also smoothes out the current to generate an absolutely even, uninterrupted signal. The output circuit's load (the work it does) is moving the speaker cone.

The input circuit is the electrical audio signal recorded on tape or running in from a microphone. Its load is modifying the output circuit. It applies a varying resistance to the output circuit to re-create the voltage fluctuations of the original audio signal.

In most amplifiers, this load is too much work for the original audio signal. For this reason, the signal is first boosted by a pre-amplifier, which sends a stronger output signal to the power amplifier. The pre-amplifier works the same basic way as the amplifier: The input circuit applies varying resistance to an output circuit generated by the power supply. Some amplifier systems use several pre-amplifiers to gradually build up to a high-voltage output signal.

Inside an amplifier, there are a lot of electronic components. The central components are the large transistors. The transistors generate a lot of heat, which is dissipated by the heat sink.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 9

Read the text: Microprocessors

The microprocessor is sometimes referred to as the 'brain' of the personal computer, and is responsible for the processing of the instructions which make up computer software. It houses the central processing unit, commonly referred to as the CPU.

Arithmetic & Logic Unit (ALU) deals with operations such as addition, subtraction, and multiplication of integers and Boolean operations. It receives control signals from the control unit telling it to carry out these operations. Control Unit (CU) controls the movement of instructions in and out of the processor, and also controls the operation of the ALU. It consists of a decoder, control logic circuits, and a clock to ensure everything happens at the correct time. It is also responsible for performing the instruction execution cycle. Register Array -is a small amount of internal memory that is used for the quick storage and retrieval of data and instructions. All processors include some common registers used for specific functions, namely the program counter, instruction register, accumulator, memory address register and stack pointer. System Busis comprised of the control bus, data bus and address bus. It is used for connections between the processor, memory and peripherals, and transferal of data between the various parts. Memoryis not an actual part of the CPU itself, and is instead housed elsewhere on the motherboard. However, it is here that the program being executed is stored, and as such is a crucial part of the overall structure involved in program execution.

The ALU, or the arithmetic and logic unit, is the section of the processor that is involved with executing operations of an arithmetic or logical nature. It works in conjunction with the register array for many of these, in particular, the accumulator and flag registers. The accumulator holds the results of operations, while the flag register contains a number of individual bits that are used to store information about the last operation carried out by the ALU.

Addition and subtractionare performed by constructs of logic gates, such as half adders and full adders. While they may be termed 'adders', with the aid of they can also perform subtraction via use of inverters and 'two's complement' arithmetic. In most modern processors, the multiplication and division of integer values are handled by specific floating-point hardware within the CPU. Earlier processors used either additional chips known as maths co-processors, or used a completely different method to perform the task. Further logic gates are used within the ALU to perform a number of different logical tests, including seeing if an operation produces a result of zero. Most of these logical tests are used to then change the values stored in the flag register, so that they may be checked later by separate operations or instructions. Others produce a result which is then stored, and used later in further processing.

Comparisonoperations compare values in order to determine such things as whether one number is greater than, less than or equal to another. These operations can be performed by subtraction of one of the numbers from the other, and as such can be handled by the aforementioned logic gates. However, it is not strictly necessary for the result of the calculation to be stored in this instance, the amount by which the values differ is not required. Instead, the appropriate status flags in the flag register are set and checked to determine the result of the operation.

Bit shifting.Shifting operations move bits left or right within a word, with different operations filling the gaps created in different ways. This is accomplished via the use of a shift register, which uses pulses from the clock within the control unit to trigger a chain reaction of movement across the bits that make up the word.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 10

Read the text: The main elements of the control unit.

The decoderis used to decode the instructions that make up a program when they are being processed, and to determine in what actions must be taken in order to process them. These decisions are normally taken by looking at the operation code of the instruction, together with the addressing mode used.

The timer or clockensures that all processes and instructions are carried out and completed at the right time. Pulses are sent to the other areas of the CPU at regular intervals (related to the processor clock speed), and actions only occur when a pulse is detected. This ensures that the actions themselves also occur at these same regular intervals, meaning that the operations of the CPU are synchronised.

The control logic circuits are used to create the control signals themselves, which are then sent around the processor. These signals inform the arithmetic and logic unit and the register array what they actions and steps they should be performing, what data they should be using to perform said actions, and what should be done with the results.

A register is a memory location within the CPU itself, designed to be quickly accessed for purposes of fast data retrieval. Processors normally contain a register array, which houses many such registers. These contain instructions, data and other values that may need to be quickly accessed during the execution of a program.

Many different types of registers are common between most microprocessor designs.

Program Counter (PC)
This register is used to hold the memory address of the next instruction that has to be executed in a program. This is to ensure the CPU knows at all times where it has reached, that is able to resume following an execution at the correct point, and that the program is executed correctly.

Instruction Register (IR)
This is used to hold the current instruction in the processor while it is being decoded and executed, in order for the speed of the whole execution process to be reduced. This is because the time needed to access the instruction register is much less than continual checking of the memory location itself.

Accumulator (A, or ACC)
The accumulator is used to hold the result of operations performed by the arithmetic and logic unit.

Memory Address Register (MAR)
Used for storage of memory addresses, usually the addresses involved in the instructions are held in the instruction register. The control unit then checks this register when needing to know which memory address to check or obtain data from.

Memory Buffer Register (MBR)
When an instruction or data is obtained from the memory or elsewhere, it is first placed in the memory buffer register. The next action to take is then determined and carried out, and the data is moved on to the desired location.

Flag register / status flags
The flag register is specially designed to contain all the appropriate 1-bit status flags, which are changed as a result of operations involving the arithmetic and logic unit.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 11

Read the text: Radar System Components and System Design (1)

The radar antenna acts as the interface between the radar system and free space through which radio waves are transmitted and received. The purpose of the radar antenna is to transduce free space propagation to guided wave propagation during reception and the opposite during transmission. During transmission, the radiated energy is concentrated into a shaped beam which points in the desired direction in space. During reception, the antenna collects the energy contained in the echo signal and delivers it to the receiver.

When a single antenna is used for both transmission and reception, as in most monostatic radar systems, a duplexer must be used. A duplexer switches the radar system from transmit mode to receive mode. There are four main requirements that must be met by an effective radar duplexing system. During transmission, the switch must connect the antenna to the transmitter and disconnect it from the receiver. The receiver must be thoroughly isolated from the transmitter during the transmission of the high-power pulse to avoid damage to sensitive receiver components. After transmission, the switch must rapidly disconnect the transmitter and connect the receiver to the antenna. For targets close to the radar to be detected, the action of the switch must be extremely rapid. The switch should have very little insertion loss during both transmission and reception.

The simplest solution to the duplexer problem is to use a switch to transfer the antenna connection from the receiver to the transmitter during the transmitted pulse and back to the receiver during the return pulse. Since no practical mechanical switches are available that can open and close in a few microseconds, electronic switches are used. For radars with waveguide antenna feeds, waveguide junction circulators are often used as duplexers. A circulator is a nonreciprocal ferrite device, which contains three or more ports. A three-port ferrite junction circulator, called the Y-junction circulator, is most commonly used. The Y-junction circulator uses spinel ferrites or garnet ferrites in the presence of a magnetic bias field, to provide a nonreciprocal effect.

If a signal is applied at the transmitter port, it will emerge from the antenna port with a loss characteristic called insertion loss. Typical values of insertion loss are 0.1 to 0.5 dB. In the reverse direction, there will be leakage at the receiver port from the incoming signal at the transmitter port. This leakage, called isolation, is typically 20 dB below incoming power at the transmitter port. Due to the symmetry of the Y-junction, the behavior is the same for the other ports, with respect to other port pairs.

The Radio Frequency (RF) system takes a signal from the transmitter and eventually propagates it in free space during transmission. The RF system takes a signal from free space and passes it to the receiver during reception. The RF system generally consists of an antenna feed and antenna, a duplexer, and some filters. Often devices are needed to convert waveguide propagation into coaxial cable propagation. Filtering is used to attenuate out-of-band signals such as images and interference from other radars or high-powered electrical devices during reception. During transmission, filtering is used to attenuate harmonics and images. The preselector filter is a device that accomplishes these two filtering objectives. The duplexer provides isolation between the transmitter and receiver to protect the sensitive receiver during the high energy transmit pulse. The antenna feed collects energy as it is received from the antenna or transmits energy as it is transmitted from the antenna. The antenna is the final stage in the RF system during transmission or the first stage during reception.

Digital waveform generators are constructed by linking a digital signal source with a digital to analog (D/A) converter. In general, digital memories are used to store the signal waveform. The memory is read out based on the timing characteristics of the desired waveform.

There is a great deal of flexibility with digital waveform generators, which is not present for analog signal generators.

1. Write down the key-words that help you to catch the main idea of the text

2. Write down all the unknown words and translate them with a dictionary.

3. Pick out the basic information of every paragraph.

4. Put five questions to the text.

5. Summarize the information from the text in some sentences.

Lesson 12

Read the text: Radar System Components and System Design (2)

The purpose of a low noise amplifier (LNA) is to boost the desired signal power while adding as little noise and distortion as possible so that retrieval of this signal is possible in the later stages in the system. An LNA is an amplifier with low noise figure. Noise figure is defined as the input signal to noise ratio (SNR) divided by the output SNR. For an amplifier, it can also be interpreted as the amount of noise introduced by the amplifier seen at the output besides that which is caused by the noise of the input signal. LNAs are used as the front end of radar receivers. There are a few different kinds of amplifiers that can provide suitably low noise figures. Parametric amplifiers have low noise figure, especially at high microwave frequencies.

The transistor amplifier can be applied over most of the range frequencies used for radar. The silicon bipolar transistor and the gallium arsenide field effect transistor have also been used as amplifiers. The lower the noise figure of the receiver, the less need there is for the transmitter power for the same performance. In addition to noise figure, cost, burnout, and dynamic range must also be considered when selecting a receiver front end.

The function of the radar receiver is to detect wanted echo signals in the presence of noise, clutter, and interference. It must separate desired signals from undesired signals, and amplify the desired signals for later processing. Receiver design depends on the design of the transmitted waveform, the nature of the targets, and the characteristics of noise, clutter, and interference. The goal of receivers is to maximize the SNR of the returned echo signal. The receiver system generally consists of an LNA, and downconverting mixers. Limiters are often built into the front end to prevent inadvertent damage from reflected transmitter power or the high power signal which may enter the system. Sometimes analog to digital (A/D) converters are placed at the end of the receiver signal path, if digital signal processing is to take place.


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