第三单元:
transistor 晶体管 emitter 发射极collector 集电极 base n. 基极 capacitor 电容 gain 增益 couple 耦合 impedance 阻抗 current 电流 filter 滤波器 oscillator n.振荡器 comparator 比较器 amplification 放大 offset 偏移 swing 摇摆 invert 颠倒 saturation 饱和度 IC=Integrated circuit 集成电路 common emitter circuit 共射级电路 load resistor 负载电阻 in series with 与....... 串联 short circuit 短路 op-amps=operational amplifiers 运算放大器 differential amplifier 差分放大器
Analog circuit 模拟电路 the voltage at the non-inverting input通向输入端电压 the voltage at the inverting input反相端输入电压
第八单元：
telecommunication 电信 telephony 电话 switchboard 交换台 electromechanical 电机的 crossbar 纵横 analog 模拟 repeater 转发器 quadrature 正交 hierarchy 分层 protocol 协议 compatibility 兼容性 interconnect 相互连接 cellular 蜂窝状的 spectrum 频谱 subscriber 用户copper 铜 dialing pulse 拨号脉冲 radio-relay transmission 无线电中继器 high-frequency 高频 very-high-frequency 甚高频 ultra-high-frequency 超高频 quadrature amplitude modulation 正交幅度调节 stored-program control 存储程序控制pulse code modulation 脉冲编码调制open-system-interconnection 开放系统互联 local area networks 局域网converge on 集中于 be regarded as 被认为是 as long as 只是step by step 步进制 electronic switch 电子交换机 long-distance-network 长途网 dialing pulse 拨号脉冲 radio-rely 无线电中继 civil communication satellite民用通信卫星 digital microwave数字微波packet switching 分组交换 data communication 数据通信 dial-up terminal 拨号终端 host computer 主计算机mobile communication 移动通信 television programs 电视节目 optical fiber 光纤 the American Standard Code for Information Interchange 美国信息标准代码the International Organization of Standardization 国际标准组织
第九单元:
numerical adj. 数值的 aliasing n. 混叠现象reciprocal adj. 互惠的，倒数的；n. 倒数 precede v. 领先(于), 在…之前, 先于 digitization n.比例, 均衡, 部分;vt. 使成比例, 使均衡, 分摊
smoothing n. 平滑(滤波) infinite n. 无限, 无穷大;adj. 无穷的, 无限的 erroneous adj. 错误的, 不正确的 baseband n.基带 deduce vt.推导, 演绎 spectrum n.光谱, 频谱 incredibly adv.难以置信的; 可疑的 budget n. 预算;vi. 做预算, 编入预算 trick n. 窍门, 诀窍, 恶作剧, 诡计, 骗局;vt. 欺骗, 哄骗 simultaneously adv.同时地 simulation n.模拟 emulation n. 仿真, 效法; 竞争 alternative n.二中选一, 可供选择的办法;adj. 选择性的, 二中选一的 reconfigurable adj. 可重新配置的, 可重构的 iterative adj.反复的, 重复的, 迭代的 foundry n. 主张, 建议, 陈述, 命题 impediment n. 妨碍, 阻碍, 障碍物 encumber v. 阻碍, 拖累 compatibility n.[计]兼容性 embrace vt. 拥抱, 包含;vi. 拥抱;n. 拥抱 appliance n. 用具, 器具sample and hold circuit 采样保持电路 sampling interval (period,frequency) 采样间隔(周期, 频率) Nyquist theorem奈奎斯特定理 hold time 保持时间 anti-aliasing filter 抗混叠滤波器 low pass 低通quantizatiaon level(step) 量化电平(间隔) acquisition time 采样时间 full scale range 满量程范围 dynamic range 动态范围 signal-to-noise ratio 信噪比 zero-order hold 零阶保持 staircase-liked 接地形状的 time to market 上市时间 wireless infrastructure 无线基础设施 in conjunction with 与…协力 under sampling 欠采样 spectral inversion 频谱反转 price/performance ratio 性能价格比filed-programmable 现场可编程的 more often than not 时常 bus interfaces 总线接口 glue logic 互连逻辑 power dissipation 功率耗散, 功耗消耗(功耗) end product 最终产品
functionalaccelerator 性能加速器 real time 实时 hand-held 手持的, 手持式的(设备) 第十单元：
extraterrestrial 地球外的 inevitable 不可避免的 premonition 预感 asunder 分开 alas 唉 drama 剧本 ignite 点火 thermonuclear 热核的 fusion 溶解 coherent 紧凑的 pebble 卵石 monochromatic 单色的
第十一单元：
record 记录 field 字段 database 数据库 data management 数据库管理
第十二单元：
streamline 合理化 ISDN(Integrated Services Digital Network) 综合业务数字网 CAI(Computer-Aided-Instruction)计算机辅助教学 PBX (Private Branch Exchange) 用户系小交换机或专用交换机
第十五单元：
reservation 保留 graphics 图示 inventory 清单 teleprocessing 远程信息处理 constrain 约束的 multi-access 多路存取 feedback 反馈 intelligence 智能 intermediate 中间的 elapse 消失，经过be called upon on 用来..... With the aid of 借助于 appear as 作为....... 出现 be likely to 可能，大约
第三单元
1、 the output of the differential amplifier is fed to the circuit ’s output stage via an
offset-compuensationnetwork,which cause the op-amp ’s output to center at zero volts.The output stage takes the form of a complementary emitter follower,and provides a low-impedance output.
差分放大器的输出通过一个失调补偿网络与输出级相连，目的是使运放的输出以0V 为中心。输出级采用互补的射极跟随器的形式以使输出阻抗很低。
2、 Bacause of the very high open-loop voltage goes slightly above the reference voltage,and
driven into negative saturation(close to-V) when the sample voltage goes slightly below the reference voltage.
由于运费的开环增益很高，当取样电压略高于参考电压时，输出趋向于正向饱和状态（接近+V）。当取样电压低于参考电压时，输出趋向于负向饱和状态（接近—V ）。
3、 If the signal source were direct connected instead of capacitor coupled,therewoukd be a low
resistance path from the base to the negative supply line,and this would affect the circuit bias conditions.
如果信号源和电路不是用电容耦合而是直接相连，从基极到负极电源线就会有一个低阻通路，并且这将影响到电流偏置状态。
4、 A conventional operational amplifier(op-amps) can be simply described as a high-gain
direct-coupled voltage amplifier that has a single output terminal,and because it has both inverting and non-inverting input terminals,the device can function as an inverting, non-inverting,or differential amplifier,filter,oscillators,levelswitches,comparators,etc.
一个普通的运算放大器可以简单的描述成一个具有单端输出的、高增益的、直接耦合电压放大器。由于具有同相输入和输出二个输入端子，因此可用于同相、反相、差动放大。当给运放配以适合的反馈网络时，又可用于精密放大器、滤波器、振荡器、换能器和比较器等。
5、 The differential amplifier has a high-impedance(constant-current) ”tial ” to give it a high input
impedance and a high degree of common-mode signal rejection. It also has a high-impedance collector (or drain) load,to give it a large amount of signal -voltage
gain(typically about 100 dB).
差动放大器有一个高阻抗的“尾巴”（恒流源）以提高输入端阻抗和对共模信号的深度抑制，同时，它还具有一个高阻抗的集电极或漏极负载以提高信号电压增益（典型数据约为100dB ）。
6、 In that circuit, a fixed reference voltage is fed to the non-inverting terminal.Because of the
high open-loop voltage gain of the op-amp,the output is driven into positive saturation (close to +V) when the sample voltage goes slightly above the reference voltage,and driven into negative saturation (clode to —V) when the sample voltage goes slighty below the reference voltage.
电路中反向输入端接入一个固定的参考电压，同相输入端接入一个变化的电压或取样电压，由于运放的开环电压增益很高，当取样电压略高于参考电压时，输入趋向于正向饱和状态（接近+V）。当取样电压低于参考电压时，输出趋向于负向饱和状态（接近—V ）。 第八单元
1、 Shortly after the invention of the telephone by Alexander Graham Bell in 1876,it was realized
that telephone wires had to converge on central points where telephone -to-telephone connections could be made.
在1876年亚历山大. 格雷厄姆. 贝尔发明电话不久，人们就认识到电话线必须在进行电话与电话接续的中心点集中。
2、 Crossbar switching was carried out by a special circuit called a marker,which provided
common control of number entry and line selection for all calls.
纵横制交换由一个称为标识器的特定电路控制，标志器提供整个号码的公共控制并选择所有呼叫的路由。
3、 The principle of converting analog signals to digital signals became popular with the
introduction of pulse code modulation(PCM); consequently,the known rate for telephone-quality speech(4 kHz bandwidth) is 64 kbps.
随着脉冲编码器调制（PCM ）技术的出现，把模拟信号转换为数字信号的原理得到广泛应用；对于电话质量的话音（4 kHz带宽），工人的数字化速率为64 kb/s。
4、 As data networks asvanced from terminal-oriented systems to
packet-switched,computer-to-computterlinkuosmtheprococols necessary to make networks function also grew more computer.
由于数据网络从面向终端的系统向分组交换、计算机与计算机连接的方向发展，执行网络功能所必须的协议也变得越来越复杂。
5、 Working closely with CCITT,the International Organization of Standardization (IOS) in 1978
approved its seven-layer framework of protocols for data communications,called the Open-System-Interconnection(OSI) reference model.
与CCITT 紧密协作的国际标准化组织（IOS ）于1978年通过数据通信的七层协议结构，称为开放系统互连（OSI ）参考模型。
第九单元
1、 Depending on the relationship between the signal frequencies and the sampling rate,spectral
inversion may cause the shape of the spectrum in the baswband to be inverted from the true spectrum of the signal.
根据信号频率和采样频率之间的关系的不同，可能出现“频谱反转”现象——基带频谱的形状和信号真实频谱的形状正好相反。
2、 If a universal microprocessor solution existed with which every design could
realized,theelectronics industry wouldn’t be a very competitive place.
假如存在可用于现实任何设计的通用微处理器的话，电子行业就不会竞争得如此激烈了。
3、 As such,every new version of the product requires a redesign and trips throough the
foundry,an expensive proposition,and an impediment to rapicd time-to-mark.
而且，每次推出一个新产品都需要重新设计并经历所有制造流程。这样做不但造价昂贵，而且不利于迅速上市。
4、 However,for applications in which the end product must process answers in real time,or must
do so while powered by consumer batteries,GPPs comparatively poor real time performance and high power consumption all but rules them out.
然而，在最终产品必须实时响应的应用中，或者必须在电池供电下实现实时响应的应用中，由于GPP 实时性能较差、功耗大，因此就被排除在外了。
5、 The first step in converting an analog signal is sampling.This step is accomplished using a
sample and hold circuit ,which grabs a sample from the signal and holds it steady until the next sampling time ,sample are normally collected at regular time intervals,,called sampling periods.If the rate of the sampling is not adequate ,distortion called aliasingcan occur ,The output from the sample and hold circuit is passed to an A/D converter,which chooses a quantization level that is closest to the actual amplitude of the signal.This is the second step in A/Dconverter:for N bits ,2n level are possible .Since analog amplitudes cannot in general be represented perfectly in a digital system ,quantization errors occur.
模拟信号向数字信号转换的第一步是采样。它是通过使用采样保持电路来实现的，该电路从信号当中获取一个样本，并保持其稳定到下一个采样时刻。通常，样本是按照固定时间间隔采集的，这个时间间隔被称为采集周期。如果采集率不够的话，一种称作“混 的畸变就会出现。采样保持电路的输出被送到一个模/数转换器。该转换器选择一个最接近信号实际幅度的量化电平。这是模/数转换的第二步。可供选择的电平数取决于转换器使用的位数:对于N 位转换器，可能的电平数为2n 。由于数字系统无法完全表示模拟幅度，因此就会出现量化误差。
6、 Digital signal processing can be divided into two categories ,fixed point and float
point .Theses refer to the format used to store and manipulate numbers whithin the devices .Fixed point DSPs usually represent each number with a minimum of 16 bits;floating point DSPs typically use a minimum of 32 bits to store each value.
数字信号处理可分为定点和浮点两大类。定点和浮点指的是期间内用于存储和操作数据的格式。定点数字信号处理通常用最少16位来表示每个数据，典型的浮点数字信号处理器用最少32位来存储每个数据。
7、 DSPs are programmed in the same language as other scientific and engineering
applications,usually assembly or C.however,DSPprograms are different from traditional software tasks in two important respects .First ,the programs are usually much shorter,say,one hundred lines versus ten thousand lines .Second,the execution speed is often a critical part of the application.
和其他科学和工程应用一样，数字信号处理器通常使用汇编语言或则C 语言进行编程。然而，DSP 程序和传统软件任务不同。首先，程序通常短得多，如100行而不是1万行。其次，执行速度往往是其应用的关键部分
第十单元
1、 Intensity is a measure of power per unit area, and even a laser that emits only a few milli-watts can produce a lot of intensity in a beam that’s only a millimeter in diameter.
强度是每单位面积上能量的度量，即使一个仅产生几毫瓦能量的激光器也能产生一个直径只有1毫米的高强度光束
2、Laser beams have been produced in every color of the rainbow (red is the most common laser color), as well as in many kinds of invisible light, but each laser can emit one color and one color only.
激光束可以是彩虹中的每一种颜色（红色是常见的激光颜色），还可以是许多种看不见的光，但每个激光器能且只能发出一种颜色。
第十一单元
1、By contrast, a file management system is software that allows the user to create, maintain, andaccess one file at a time.
相反, 文件管理系统则是允许用户在某一时刻生成、维护和访问一个文件的软件。
2、Since the responsibility for accessing the physical data rests with the database management system, the programmer can ignore the physical data structure.
由于存取实际数据的责任由数据库系统承担，因此程序员就可以不考虑实际的数据结构。
3、A non-management employee would probably have no access privileges to the payroll data and could neither inquire about nor change the data.
而非管理型员工则可能没有访问工资数据的权利, 他们既不能查询也不能对数据进行修改。
第十二单元
1、 This network could enhance communications between teachers and staff, allowing students
to gain more of their teacher’s time for instruction, personal attention, and an enriched curriculum.
这个网络可以加强教职员之间的交流，使得老师们有更多的时间用来给学生们授课、个别辅导，以及开设更多的课程。
2、 Furthermore, this information would be available to the patient’s private physician and to
this (or another) hospital in case of a subsequent readmission or transfer to another facility. 而且，万一在以后重进医院或转入其他地方，病人的私人大夫和这家（或其他）医院都可以看到这些信息资料。
3、 The capabilities mentioned in the paragraphs above are all possible; it remains only for the
applications and products to be designed to take advantage of this communications technology.
上面提到的功能都是可能的，现在要做的只是更好地运用通信技术来设计产品并加以应用。
第十五单元
1、 The combination of computers and data communication places such new requirements on
the systems, which must handle them, that one can refer to them better as teleprocessing rather than telecommunications.
计算机和数据通信的结合向系统提出必须对这些信息进行处理的新要求，以至人们最好称它们为远程信息处理，而不是远程通信。
2、 Several different types of computer peripherals may appear as network terminals, and so
also can computers functioning in several different ways.
几种不同的计算机外围设备可能作为网络终端出现，几种不同方式运行的计算机也可能作为网络终端出现。
3、 The access times for typical computers in use at this time are about 100 ms, but this will
become faster as better memories are utilized.
目前所用的典型计算机存取时间大约为100毫秒，但当采用较好的存储器时，存取时间将会缩短。
4、 It is apparent that current is (directly) proportional to the applied voltage.
显然电流与外加电压成正比。
5、 It has been found that metals are all good conductors.
人们发现的金属都是良导体。
6、 The efficiency of the machine depends on how fast it can run.
该机器的效率取决于它能运转得多快。
7、 Do you know what the potential difference is?
你知道电位差是什么吗？
8、 As we shall see,velocity is a vector.
正如我们将会看到的那样, 速度是一个矢量。
9、 These instruments are just what we need.
这些仪器正是我们需要的。
10、 By no means do electrons in a wire flow from the positive to the negative.
导线中的电子绝不能从正流向负。
11、 Every substance,be it water,iron or air,consists of atoms.
所有物质, 不论是水、铁还是空气, 都是由原子构成的。
第三单元:
transistor 晶体管 emitter 发射极collector 集电极 base n. 基极 capacitor 电容 gain 增益 couple 耦合 impedance 阻抗 current 电流 filter 滤波器 oscillator n.振荡器 comparator 比较器 amplification 放大 offset 偏移 swing 摇摆 invert 颠倒 saturation 饱和度 IC=Integrated circuit 集成电路 common emitter circuit 共射级电路 load resistor 负载电阻 in series with 与....... 串联 short circuit 短路 op-amps=operational amplifiers 运算放大器 differential amplifier 差分放大器
Analog circuit 模拟电路 the voltage at the non-inverting input通向输入端电压 the voltage at the inverting input反相端输入电压
第八单元：
telecommunication 电信 telephony 电话 switchboard 交换台 electromechanical 电机的 crossbar 纵横 analog 模拟 repeater 转发器 quadrature 正交 hierarchy 分层 protocol 协议 compatibility 兼容性 interconnect 相互连接 cellular 蜂窝状的 spectrum 频谱 subscriber 用户copper 铜 dialing pulse 拨号脉冲 radio-relay transmission 无线电中继器 high-frequency 高频 very-high-frequency 甚高频 ultra-high-frequency 超高频 quadrature amplitude modulation 正交幅度调节 stored-program control 存储程序控制pulse code modulation 脉冲编码调制open-system-interconnection 开放系统互联 local area networks 局域网converge on 集中于 be regarded as 被认为是 as long as 只是step by step 步进制 electronic switch 电子交换机 long-distance-network 长途网 dialing pulse 拨号脉冲 radio-rely 无线电中继 civil communication satellite民用通信卫星 digital microwave数字微波packet switching 分组交换 data communication 数据通信 dial-up terminal 拨号终端 host computer 主计算机mobile communication 移动通信 television programs 电视节目 optical fiber 光纤 the American Standard Code for Information Interchange 美国信息标准代码the International Organization of Standardization 国际标准组织
第九单元:
numerical adj. 数值的 aliasing n. 混叠现象reciprocal adj. 互惠的，倒数的；n. 倒数 precede v. 领先(于), 在…之前, 先于 digitization n.比例, 均衡, 部分;vt. 使成比例, 使均衡, 分摊
smoothing n. 平滑(滤波) infinite n. 无限, 无穷大;adj. 无穷的, 无限的 erroneous adj. 错误的, 不正确的 baseband n.基带 deduce vt.推导, 演绎 spectrum n.光谱, 频谱 incredibly adv.难以置信的; 可疑的 budget n. 预算;vi. 做预算, 编入预算 trick n. 窍门, 诀窍, 恶作剧, 诡计, 骗局;vt. 欺骗, 哄骗 simultaneously adv.同时地 simulation n.模拟 emulation n. 仿真, 效法; 竞争 alternative n.二中选一, 可供选择的办法;adj. 选择性的, 二中选一的 reconfigurable adj. 可重新配置的, 可重构的 iterative adj.反复的, 重复的, 迭代的 foundry n. 主张, 建议, 陈述, 命题 impediment n. 妨碍, 阻碍, 障碍物 encumber v. 阻碍, 拖累 compatibility n.[计]兼容性 embrace vt. 拥抱, 包含;vi. 拥抱;n. 拥抱 appliance n. 用具, 器具sample and hold circuit 采样保持电路 sampling interval (period,frequency) 采样间隔(周期, 频率) Nyquist theorem奈奎斯特定理 hold time 保持时间 anti-aliasing filter 抗混叠滤波器 low pass 低通quantizatiaon level(step) 量化电平(间隔) acquisition time 采样时间 full scale range 满量程范围 dynamic range 动态范围 signal-to-noise ratio 信噪比 zero-order hold 零阶保持 staircase-liked 接地形状的 time to market 上市时间 wireless infrastructure 无线基础设施 in conjunction with 与…协力 under sampling 欠采样 spectral inversion 频谱反转 price/performance ratio 性能价格比filed-programmable 现场可编程的 more often than not 时常 bus interfaces 总线接口 glue logic 互连逻辑 power dissipation 功率耗散, 功耗消耗(功耗) end product 最终产品
functionalaccelerator 性能加速器 real time 实时 hand-held 手持的, 手持式的(设备) 第十单元：
extraterrestrial 地球外的 inevitable 不可避免的 premonition 预感 asunder 分开 alas 唉 drama 剧本 ignite 点火 thermonuclear 热核的 fusion 溶解 coherent 紧凑的 pebble 卵石 monochromatic 单色的
第十一单元：
record 记录 field 字段 database 数据库 data management 数据库管理
第十二单元：
streamline 合理化 ISDN(Integrated Services Digital Network) 综合业务数字网 CAI(Computer-Aided-Instruction)计算机辅助教学 PBX (Private Branch Exchange) 用户系小交换机或专用交换机
第十五单元：
reservation 保留 graphics 图示 inventory 清单 teleprocessing 远程信息处理 constrain 约束的 multi-access 多路存取 feedback 反馈 intelligence 智能 intermediate 中间的 elapse 消失，经过be called upon on 用来..... With the aid of 借助于 appear as 作为....... 出现 be likely to 可能，大约
第三单元
1、 the output of the differential amplifier is fed to the circuit ’s output stage via an
offset-compuensationnetwork,which cause the op-amp ’s output to center at zero volts.The output stage takes the form of a complementary emitter follower,and provides a low-impedance output.
差分放大器的输出通过一个失调补偿网络与输出级相连，目的是使运放的输出以0V 为中心。输出级采用互补的射极跟随器的形式以使输出阻抗很低。
2、 Bacause of the very high open-loop voltage goes slightly above the reference voltage,and
driven into negative saturation(close to-V) when the sample voltage goes slightly below the reference voltage.
由于运费的开环增益很高，当取样电压略高于参考电压时，输出趋向于正向饱和状态（接近+V）。当取样电压低于参考电压时，输出趋向于负向饱和状态（接近—V ）。
3、 If the signal source were direct connected instead of capacitor coupled,therewoukd be a low
resistance path from the base to the negative supply line,and this would affect the circuit bias conditions.
如果信号源和电路不是用电容耦合而是直接相连，从基极到负极电源线就会有一个低阻通路，并且这将影响到电流偏置状态。
4、 A conventional operational amplifier(op-amps) can be simply described as a high-gain
direct-coupled voltage amplifier that has a single output terminal,and because it has both inverting and non-inverting input terminals,the device can function as an inverting, non-inverting,or differential amplifier,filter,oscillators,levelswitches,comparators,etc.
一个普通的运算放大器可以简单的描述成一个具有单端输出的、高增益的、直接耦合电压放大器。由于具有同相输入和输出二个输入端子，因此可用于同相、反相、差动放大。当给运放配以适合的反馈网络时，又可用于精密放大器、滤波器、振荡器、换能器和比较器等。
5、 The differential amplifier has a high-impedance(constant-current) ”tial ” to give it a high input
impedance and a high degree of common-mode signal rejection. It also has a high-impedance collector (or drain) load,to give it a large amount of signal -voltage
gain(typically about 100 dB).
差动放大器有一个高阻抗的“尾巴”（恒流源）以提高输入端阻抗和对共模信号的深度抑制，同时，它还具有一个高阻抗的集电极或漏极负载以提高信号电压增益（典型数据约为100dB ）。
6、 In that circuit, a fixed reference voltage is fed to the non-inverting terminal.Because of the
high open-loop voltage gain of the op-amp,the output is driven into positive saturation (close to +V) when the sample voltage goes slightly above the reference voltage,and driven into negative saturation (clode to —V) when the sample voltage goes slighty below the reference voltage.
电路中反向输入端接入一个固定的参考电压，同相输入端接入一个变化的电压或取样电压，由于运放的开环电压增益很高，当取样电压略高于参考电压时，输入趋向于正向饱和状态（接近+V）。当取样电压低于参考电压时，输出趋向于负向饱和状态（接近—V ）。 第八单元
1、 Shortly after the invention of the telephone by Alexander Graham Bell in 1876,it was realized
that telephone wires had to converge on central points where telephone -to-telephone connections could be made.
在1876年亚历山大. 格雷厄姆. 贝尔发明电话不久，人们就认识到电话线必须在进行电话与电话接续的中心点集中。
2、 Crossbar switching was carried out by a special circuit called a marker,which provided
common control of number entry and line selection for all calls.
纵横制交换由一个称为标识器的特定电路控制，标志器提供整个号码的公共控制并选择所有呼叫的路由。
3、 The principle of converting analog signals to digital signals became popular with the
introduction of pulse code modulation(PCM); consequently,the known rate for telephone-quality speech(4 kHz bandwidth) is 64 kbps.
随着脉冲编码器调制（PCM ）技术的出现，把模拟信号转换为数字信号的原理得到广泛应用；对于电话质量的话音（4 kHz带宽），工人的数字化速率为64 kb/s。
4、 As data networks asvanced from terminal-oriented systems to
packet-switched,computer-to-computterlinkuosmtheprococols necessary to make networks function also grew more computer.
由于数据网络从面向终端的系统向分组交换、计算机与计算机连接的方向发展，执行网络功能所必须的协议也变得越来越复杂。
5、 Working closely with CCITT,the International Organization of Standardization (IOS) in 1978
approved its seven-layer framework of protocols for data communications,called the Open-System-Interconnection(OSI) reference model.
与CCITT 紧密协作的国际标准化组织（IOS ）于1978年通过数据通信的七层协议结构，称为开放系统互连（OSI ）参考模型。
第九单元
1、 Depending on the relationship between the signal frequencies and the sampling rate,spectral
inversion may cause the shape of the spectrum in the baswband to be inverted from the true spectrum of the signal.
根据信号频率和采样频率之间的关系的不同，可能出现“频谱反转”现象——基带频谱的形状和信号真实频谱的形状正好相反。
2、 If a universal microprocessor solution existed with which every design could
realized,theelectronics industry wouldn’t be a very competitive place.
假如存在可用于现实任何设计的通用微处理器的话，电子行业就不会竞争得如此激烈了。
3、 As such,every new version of the product requires a redesign and trips throough the
foundry,an expensive proposition,and an impediment to rapicd time-to-mark.
而且，每次推出一个新产品都需要重新设计并经历所有制造流程。这样做不但造价昂贵，而且不利于迅速上市。
4、 However,for applications in which the end product must process answers in real time,or must
do so while powered by consumer batteries,GPPs comparatively poor real time performance and high power consumption all but rules them out.
然而，在最终产品必须实时响应的应用中，或者必须在电池供电下实现实时响应的应用中，由于GPP 实时性能较差、功耗大，因此就被排除在外了。
5、 The first step in converting an analog signal is sampling.This step is accomplished using a
sample and hold circuit ,which grabs a sample from the signal and holds it steady until the next sampling time ,sample are normally collected at regular time intervals,,called sampling periods.If the rate of the sampling is not adequate ,distortion called aliasingcan occur ,The output from the sample and hold circuit is passed to an A/D converter,which chooses a quantization level that is closest to the actual amplitude of the signal.This is the second step in A/Dconverter:for N bits ,2n level are possible .Since analog amplitudes cannot in general be represented perfectly in a digital system ,quantization errors occur.
模拟信号向数字信号转换的第一步是采样。它是通过使用采样保持电路来实现的，该电路从信号当中获取一个样本，并保持其稳定到下一个采样时刻。通常，样本是按照固定时间间隔采集的，这个时间间隔被称为采集周期。如果采集率不够的话，一种称作“混 的畸变就会出现。采样保持电路的输出被送到一个模/数转换器。该转换器选择一个最接近信号实际幅度的量化电平。这是模/数转换的第二步。可供选择的电平数取决于转换器使用的位数:对于N 位转换器，可能的电平数为2n 。由于数字系统无法完全表示模拟幅度，因此就会出现量化误差。
6、 Digital signal processing can be divided into two categories ,fixed point and float
point .Theses refer to the format used to store and manipulate numbers whithin the devices .Fixed point DSPs usually represent each number with a minimum of 16 bits;floating point DSPs typically use a minimum of 32 bits to store each value.
数字信号处理可分为定点和浮点两大类。定点和浮点指的是期间内用于存储和操作数据的格式。定点数字信号处理通常用最少16位来表示每个数据，典型的浮点数字信号处理器用最少32位来存储每个数据。
7、 DSPs are programmed in the same language as other scientific and engineering
applications,usually assembly or C.however,DSPprograms are different from traditional software tasks in two important respects .First ,the programs are usually much shorter,say,one hundred lines versus ten thousand lines .Second,the execution speed is often a critical part of the application.
和其他科学和工程应用一样，数字信号处理器通常使用汇编语言或则C 语言进行编程。然而，DSP 程序和传统软件任务不同。首先，程序通常短得多，如100行而不是1万行。其次，执行速度往往是其应用的关键部分
第十单元
1、 Intensity is a measure of power per unit area, and even a laser that emits only a few milli-watts can produce a lot of intensity in a beam that’s only a millimeter in diameter.
强度是每单位面积上能量的度量，即使一个仅产生几毫瓦能量的激光器也能产生一个直径只有1毫米的高强度光束
2、Laser beams have been produced in every color of the rainbow (red is the most common laser color), as well as in many kinds of invisible light, but each laser can emit one color and one color only.
激光束可以是彩虹中的每一种颜色（红色是常见的激光颜色），还可以是许多种看不见的光，但每个激光器能且只能发出一种颜色。
第十一单元
1、By contrast, a file management system is software that allows the user to create, maintain, andaccess one file at a time.
相反, 文件管理系统则是允许用户在某一时刻生成、维护和访问一个文件的软件。
2、Since the responsibility for accessing the physical data rests with the database management system, the programmer can ignore the physical data structure.
由于存取实际数据的责任由数据库系统承担，因此程序员就可以不考虑实际的数据结构。
3、A non-management employee would probably have no access privileges to the payroll data and could neither inquire about nor change the data.
而非管理型员工则可能没有访问工资数据的权利, 他们既不能查询也不能对数据进行修改。
第十二单元
1、 This network could enhance communications between teachers and staff, allowing students
to gain more of their teacher’s time for instruction, personal attention, and an enriched curriculum.
这个网络可以加强教职员之间的交流，使得老师们有更多的时间用来给学生们授课、个别辅导，以及开设更多的课程。
2、 Furthermore, this information would be available to the patient’s private physician and to
this (or another) hospital in case of a subsequent readmission or transfer to another facility. 而且，万一在以后重进医院或转入其他地方，病人的私人大夫和这家（或其他）医院都可以看到这些信息资料。
3、 The capabilities mentioned in the paragraphs above are all possible; it remains only for the
applications and products to be designed to take advantage of this communications technology.
上面提到的功能都是可能的，现在要做的只是更好地运用通信技术来设计产品并加以应用。
第十五单元
1、 The combination of computers and data communication places such new requirements on
the systems, which must handle them, that one can refer to them better as teleprocessing rather than telecommunications.
计算机和数据通信的结合向系统提出必须对这些信息进行处理的新要求，以至人们最好称它们为远程信息处理，而不是远程通信。
2、 Several different types of computer peripherals may appear as network terminals, and so
also can computers functioning in several different ways.
几种不同的计算机外围设备可能作为网络终端出现，几种不同方式运行的计算机也可能作为网络终端出现。
3、 The access times for typical computers in use at this time are about 100 ms, but this will
become faster as better memories are utilized.
目前所用的典型计算机存取时间大约为100毫秒，但当采用较好的存储器时，存取时间将会缩短。
4、 It is apparent that current is (directly) proportional to the applied voltage.
显然电流与外加电压成正比。
5、 It has been found that metals are all good conductors.
人们发现的金属都是良导体。
6、 The efficiency of the machine depends on how fast it can run.
该机器的效率取决于它能运转得多快。
7、 Do you know what the potential difference is?
你知道电位差是什么吗？
8、 As we shall see,velocity is a vector.
正如我们将会看到的那样, 速度是一个矢量。
9、 These instruments are just what we need.
这些仪器正是我们需要的。
10、 By no means do electrons in a wire flow from the positive to the negative.
导线中的电子绝不能从正流向负。
11、 Every substance,be it water,iron or air,consists of atoms.
所有物质, 不论是水、铁还是空气, 都是由原子构成的。