Electron tubes
Let’s consider a vacuum diode first. It is called a diode since only two electrodes are used. These are a cathode and an anode, or a plate. The cathode is a source of electrons but they are emitted from it only when it is heated. There are two methods of heating the cathode. These are direct heating and indirect heating. In the first case the emitting electrode is heated by the applied power. In the other case the cathode is heated by another element to which the power is supplied from a separate power supply.
Negative voltage applied on the cathode repels the emitted electrons toward the plate which attracts the electrons by its positive voltage. Thus the current flows through the tube in one direction only that is from the cathode to the anode. Since diodes have this property they are used as rectifiers of alternating current (а.с.) into direct current (d.с.) as detectors of radio signals and in switching circuits.
A triode consists of three elements. It has the same emitting and collecting electrodes like the diode. Its third electrode acts as a control element. It is called a control grid and serves for controlling the flow of electrons through the tube. It can increase or decrease the amount of current in the tube. The value of the current depends on the value of the grid voltage. Even if a smal1 negative voltage is applied on the grid it results in a large current through the tube. But when a large negative voltage is applied to the grid the current is reduced since a 1arger negative voltage repels more electrons back to the cathode and fewer electrons are able to pass between the grid wires to the plate. They can do it because of high positive voltage on the plate. The less negative voltage on the grid the larger the current in the tube. Thus, by using different values of grid voltage one can control the flow of the current through the tube. Because of this property triodes operate as amplifiers.
Упражнение III. Ответьте на вопросы.
What device is called a diode?
What is the function of the cathode?
What are the ways of heating the cathode?
What is the difference between these two ways of heating?
What is the direction of the current flow in the tube? Why?
Where are diodes used?
What are the elements of the triode?
What is the function of the control grid?
When is the current in the tube reduced? Why?
How can you control the flow of the current through the tube?
Unit IV Semiconductor Devices
Познакомьтесь с новыми словами
to compose [kƏm’pouz] – 1) составлять; 2) сочинять (музыку, стихи)
composition – 1) составление; 2) сочинение
state [’steit] – состояние
solid-state = semiconductor – полупроводниковый
silicon [’silikƏn] – кремний
pure [’pjuƏ] – чистый
purity [’pju:riti] – чистота
impurity – примесь
to define [di’fain] – определять
definition – определение
to insulate [’insjuleit] – изолировать
insulation – изоляция
insulator – изолятор, диэлектрик
to dope [doup] – легировать, вводить примеси
to provide [prƏ’vaid] – обеспечивать
to accept [Ək’sept] – принимать
acceptor – акцептор
to obtain [Əb’tein] = to get = to receive – получать
to introduce [’intrƏ’dju:s] – 1) вводить; 2) представлять, знакомить
introduction [intrƏ’d۸k∫n] – 1) введение; 2) представление
majority [mƏ’dʒoriti] – большинство
minority [mai’noriti] – меньшинство
to charge [t∫a:dʒ] – заряжать
charge – заряд
to carry [’kæri] – нести
carrier – носитель
majority charge carriers – основные носители заряда
minority charge carriers – неосновные носители заряда
hole [’houl] – дырка
to contain [kƏn’tein] – содержать (в себе)
junction [’dʒ۸nk∫n] – переход
junction transistor – плоскостной транзистор
to bais [’baiƏs] – смещать
bias – смещение
forward [’fo:wƏd] – прямой; вперед
reverse [ri’vƏ:s] – обратный
terminal [’tƏ:minƏl] – зажим, клемма
to utilize [’ju:tilaiz] = to use – использовать, применять
utilization = use = application – использование, применение
to perform [pƏ’fo:m] = to do – выполнять, совершать
performance – исполнение
as well – также (в конце предложения)
as well as – также как и
to differ [’difƏ] – отличаться
to manufacture [,mænju’fækt∫Ə] = to produce – производить
manufacturer [’mænju’fækt∫ƏrƏ] – производитель
to require [rik’waiƏ] – требовать
requirement – требование
to meet requirements – отвечать требованиям
thin [’θin] – тонкий
thick [’θik] – толстый
field-effect transistor (FET) – полевой транзистор
various [’væriƏs] – различный, разнообразный
gain [gein] – усиление; коэффициент усиления
noise [noiz] – шум
noiseless – бесшумный
source [’so:s] – 1) исток (в полев. тр-ре); 2) источник
drain [’drein] – 1) сток (в полев. тр-ре); 2) потребление тока
gate [’geit] – 1) затвор (в полев. тр-ре); 2) логический элемент
density [’densiti] – плотность
To V – Инфинитив (1-я форма)
(неопределенная форма глагола)
To V (to process) переводится
Что (с)делать? (что?)
обрабатывать / обработать (обработка)
Для чего?
а) (для того) чтобы обработать
б) для обработки
Какой?
а
)
to
V:
который
должен обрабатывать
может
б ) to be Ved:
1 )который должен быть обработан 2)который нужно обработать
может можно