Unit 1 Introduction to Electronic Components
Part I Technical and Practical Reading
Reading A Electronic Components — Passive Components
The main components used in electronics are of two general types：passive（e.g. resistors and capacitors）and active（e.g. transistors and integrated circuits）. The main difference between active and passive components is that active ones require to be powered in some way to make them work.
The Resistor
A resistor（Figure 1-1）is a piece of material that obeys Ohm's Law. The name comes from its main property；it resists the flow of charge through itself，hence allowing us to control the current. Resistors can be made of various kinds of material，but whatever the choice it must conduct some electricity otherwise it wouldn't be of any use.
Figure 1-1
Two wires are connected to opposite ends of the resistor（Figure 1-2）. When we apply a potential difference between the wires we set up a current from one wire to the other，through the resistor. The size of the current is proportional to the difference in voltage between the wires. The resistance（in units of Ohms）is defined as the ratio of the applied voltage，V（in Volts），divided by the current，I（in Amps），produced by the applied voltage.
Figure 1-2
The value is usually displayed using standard colour code（Figure 1-3）.
Figure 1-3
The Capacitor
If you look at a catalogue of electronic components you'll find an enormous variety of sizes and types of capacitors. However，for most purposes we can divide capacitors into two basic types：dielectric and electrolytic.
A capacitor acts as a charge store（Figure 1-4）. It contains a pair of metal plates separated by a thin sheet of insulating material. The plates are electrically neutral—the number of positive protons in each exactly equals the number of negative electrons.
Figure 1-4
However，if we connect wires to the plates and apply external voltage we can drag electrons off one plate and push them on to the other.
This takes energy，i.e. we have to do work charging the capacitor. The result is a capacitor with one plate positively charged and the other negatively charged. The energy used to move charge is stored by this imbalance. If we connect two plates together with a resistor，the electrons“rush back home”releasing their energy again. The voltage between the plates of a charged capacitor is proportional to the amount of charge moved. The charge/voltage ratio for any specific capacitor is called the capacitance（Figure 1-5）.
Figure 1-5
The Diode
There are a number of different electronic devices which tend to be called diodes（Figure 1-6）. Although they're made differently they all have three things in common.
Figure 1-6
• They have two leads like a resistor.
• The current they pass depends upon the voltage between the leads.
• They do not obey Ohm's Law！
As an example we will use a typical diode called a pn-junction. This allows us to explain behavior of diodes. Remember，however，that there are other sorts of diodes which are built differently but show the same general behavior.
We create a pn-junction by joining together two pieces of semiconductor，one doped n-type，the other p-type. This causes a depletion zone to form around the junction（the join）between the two materials. This zone controls the behavior of the diode.
Notes
1. When we apply a potential difference between the wires we set up a current from one wire to the other，through the resistor. 本句是由When …引导的时间状语从句。本句可译为：当在两根导线间施加一个电势差时，就会有电流通过电阻器从一根导线传递到另一根导线。
2. If we connect wires to the plates and apply an external voltage we can drag electrons off one plate and push them on to the other. 本句是由If …引导的条件状语从句，we can drag…为主句部分。本句可译为：如果我们将导线连接到金属板上，并且外加电压，就可以把电子从一块金属板拖到另一块上。
3. There are other sorts of diodes which are built differently but show the same general behavior. 本句为简单句，可译为：有很多别的以不同方式制作的二极管，但它们的一般性能相同。
New Words
electronic [] a. 电子的
component [] n. 元件
electronics [] n. 电子学
passive [] a. 无源的
active [] a. 有源的
resistor [] n. 电阻器
capacitor [] n. 电容器
transistor [] n. 晶体管
integrated [] a. 集成的
circuit [] n. 电路
ohm [] n. 欧姆
property [] n. 性能
charge [] n. 电荷；v. 充电
current [] n. 电流
conduct [] v. 导电
electricity [] n. 电
potential [] n. 电势
wire [] n. 导线
voltage [] n. 电压
resistance [] n. 电阻
ratio [] n. 比率
apply [] v. 施加
amp [] n. 安培
volt [] n. 伏特
value [] n. 值
dielectric [] a. 电介质的
electrolytic [] a. 电解质的
plate [] n. 金属板
sheet [] n. 薄板
insulate [] v. 绝缘
neutral [] a. 中性的
positive [] a. 正的
proton [] n. 质子
negative [] a. 负的
electron [] n. 电子
imbalance [] n. 不平衡
release [] v. 释放
capacitance [] n. 电容
diode [] n. 二极管
lead [] n. 引线
junction [] n. 结
behavior [] n. 性能
semiconductor [] n. 半导体
dope [] v. 掺杂
depletion [] n. 耗尽
join [] n. 结；v. 焊接
Phrases and Expressions
electronic component 电子元件
passive component 无源元件
active component 有源元件
integrated circuit（IC） 集成电路
Ohm's Law 欧姆定律
potential difference 电势差
be proportional to 与……成正比，与……成比例
in units of 单位为
be defined as 定义为
applied voltage 施加电压
insulating material 绝缘材料
positive proton 正质子
negative electron 负电子
do work 做功
electronic device 电子器件
pn-junction pn结
depletion zone 耗尽层
EXERCISE 1
Match the picture with the correct components.
A. Transistor
B. Diode
C. Capacitor
D. Resistor
E. Connector
F. LED
EXERCISE 2
Translate the following phrases into Chinese or English.
Reading B Electronic Components — Active Components
Junction Field Effect Transistors
Junction field effect transistors（JFETs）come in two“flavors”，p-channel and n-channel（Figure 1-7）. In each case a bar，or channel，of one type of semiconductor material is located inside a bulk material of the other kind，i.e. p inside n，or n inside p.
Figure 1-7
A pair of metallic contacts is placed at each end of the channel. When we apply a voltage between these，a current can flow along the channel from one contact to the other. The contact which launches charges along the channel is called the source；the one that“eats”them at the other end is called the drain.
In an n-channel device，the channel is made of n-type semiconductor，so the charges free to move along the channel are negatively（hence n）charged—they are electrons. In a p-channel device the free charges which move from end-to-end are positively（hence p）charged—they are holes（Figure 1-8）. Remember that a hole is the absence of an electron. In each case the source puts fresh charges into the channel while the drain removes them at the other end.
Figure 1-8
Bipolar Transistor
A Bipolar Transistor（Figure 1-9）essentially consists of a pair of PN Junction Diodes that are joined back-to-back. This forms a sort of a sandwich where one kind of semiconductor is placed in-between two others. There are therefore two kinds of bipolar sandwich，the NPN and PNP varieties. The three layers of the sandwich are conventionally called the Collector，Base，and Emitter. The reasons for these names will become clear later once we see how the transistor works.
Figure 1-9
Some of the basic properties exhibited by a Bipolar Transistor are immediately recognizable as being diode-like. However，when the“filling”of the sandwich is fairly thin some interesting effects become possible that allow us to use the Transistor as an amplifier or a switch. To see how the Bipolar Transistor works we can concentrate on the NPN variety.
Figure 1-10 shows the energy levels in an NPN transistor when we aren't externally applying any voltages. We can see that the arrangement looks like a back-to-back pair of PN Diode junctions with a thin P-type filling between two N-type slices of“bread”. In each of the N-type layers conduction can take place by the free movement of electrons in the conduction band. In the P-type（filling）layer conduction can take place by the movement of the free holes in the valence band. However，in the absence of any externally applied electric field，we find that depletion zones form at both PN-Junctions，so no charge wants to move from one layer to another.
Figure 1-10
Consider now what happens when we apply a moderate voltage between the Collector and Base parts of the transistor. The polarity of the applied voltage is chosen to increase the force pulling the N-type electrons and P-type holes apart（Figure 1-11）. This widens the depletion zone between the Collector and Base，and so no current will flow.
Figure 1-11
In effect we have reverse-biased the Base- Collector diode junction. The precise value of the Base-Collector voltage we choose doesn't really matter to what happens provided we don't make it too big and blow up the transistor！
New Words
field [] a. 现场的；n. 场
effect [] n. 效应
flavor [] n. 特点，特色
channel [] n. 沟道
bulk [] n. 大块，体积
gate [] n. 门极，栅极
source [] n. 源极
drain [] n. 漏极
metallic [] a. 金属的
contact [] n. 触点
launch [] v. 释放
hole [] n. 空穴
view [] n. 视图
bipolar [] a. 双极的
layer [] n. 层
collector [] n. 集电极
base [] n. 基极
emitter [] n. 发射极
exhibit [] v. 呈现
amplifier [] n. 放大器
level [] n. 电平，液面，等级
arrangement [] n. 排列
conduction [] n. 导电
band [] n. 带
valence [] n. 原子价
polarity [] n. 极性
reverse-bias [] v. 反向偏压
Phrases and Expressions
Junction Field Effect Transistors（JFETs） 结型场效应晶体管
p-channel p沟道
n-channel n沟道
bulk material 松散材料
metallic contact 金属触点
electric field 电场
view from above 俯视图
Bipolar Transistor 双极型晶体管
PN Junction Diode PN结二极管
energy level 能级
conduction band 导电带
valence band 价电子带
blow up 熔断
EXERCISE 3
Choose the correct components.
EXERCISE 4
Abbreviations are very useful. Read them and then translate them into corresponding Chinese terms.
