Text A
Analog Circuits and Digital Circuits
　　Both analog circuits and digital circuits are extensively used in various fields of electrical and electronic engineering for signal processing. 
1. What Is an Analog Circuit?
　　An analog circuit is a type of electronic circuit that can process any analog signal and  produce an output in analog form (see Figure 5-1). Analog circuits are composed of resistors, inductors and capacitors, etc. 

Figure 5-1  Simple Analog Circuit
　　The type of signal which is a continuous function of time is known as an analog signal. All the real-world signals are the analog signals, therefore, the analog circuit do not require any  conversion of the input signal i.e. the analog input signal can be directly fed to the analog circuit without any loss and it can be directly processed by the given analog circuit. Also, the output signal produced by the analog circuit is an analog signal.
　　Based on the circuit behavior and the components used, the analog circuit can be of two types. They are active circuit and passive circuit. Amplifiers are the examples of active analog circuit while low pass filter is an example of passive circuit. The main drawback of the analog circuits is that the analog signals are very susceptible to noises, and the noises may cause    distortion of the signal waveform and the loss of information.
2. What Is a Digital Circuit?
　　A digital circuit is an electronic circuit that processes digital signals. A signal that is a    discrete function of time is known as a digital signal.
　　The basic building blocks of digital circuits are digital logic gates (see Figure 5-2). The  digital circuit can process only digital signals, but the real-world signals are of analog nature. Therefore, they need to be converted into digital signals using special electronic circuit known as  analog to digital converter (ADC). The output of the digital circuits is also digital signals, which is required to be converted back into the analog signal.

Figure 5-2  Simple Digital Circuit
　　There may be loss of information in the digital circuit during sampling process. The digital circuits can only be active circuits, which means they require an additional power source to  power the circuit. [1] 
3. Difference Between Analog Circuit and Digital Circuit
　　The following Table 5-1 highlight the major differences between analog circuits and digital circuits.
Table 5-1  Difference between analog circuit and digital circuit
Parameter
Analog Circuit
Digital Circuit
Definition
The electronic circuit which can process only analog signals is known as analog circuit.
The electronic circuit which can process only digital signals is known as digital  circuit.
Input signal
The input signal to the analog circuit must be a continuous time signal or analog signal.
The input signal to the digital circuit is a discrete time signals or digital signal.
Output signal
Analog circuits produces output in the form of analog signals.
The output of the digital circuit is a digital signal.
Circuit components
The circuit components of the analog circuits are resistors, inductors, capacitors, etc.
The main circuit components of the digital circuits are logic gates.
Need of converters
The analog circuits can process the analog signals which exist in the nature directly. Therefore, analog circuits do not require signal converters.
The digital circuits can process signals only in digital form. Thus, digital circuits require signal converter, i.e. analog to digital  converter (ADC) and digital to analog  converter (DAC).
Susceptibility to 
noise
The analog signals are more susceptible to noises.
The digital signals are immune to noises.
                                                                                   续表    
Parameter
Analog Circuit
Digital Circuit
Design
The analog circuits are complex to design because their circuit components need to be placed manually.
The designing of complicated digital   circuits is relatively easier by using multiple software.
Flexibility
The implementation of analog circuit is not flexible.
The digital circuits offer more flexible  implementation process.
Types
Analog circuits can be of two types: active circuit and passive circuit.
Digital circuits are of only one type named active circuit.
Processing speed
The processing speed of analog circuits is relatively low.
The digital circuits have higher processing speed than analog circuits.
Power consumption
The analog circuits consume more power.
The power consumed by the digital circuits is relatively less.
Accuracy & 
precision
The analog circuits are less accurate and precise.
The digital circuits are comparatively more accurate and precise.
Observational errors
In case of analog circuits, there may be an observational error in the output.
The digital circuits are free from observational errors in the output.
Signal transmission
In case of analog circuits, the signals are transmitted in the form of waves either wirelessly or with wires.
In the digital circuits, the signals can only be transmitted through wires in the digital form.
Form of information storage
The analog circuits store the information in the form of waves.
Digital circuits store the information in  binary form.
Logical operations
The analog circuit are not able to perform the logical operations efficiently.
Digital circuit performs logical operations efficiently.
4. Analog to Digital Converters
　　Analog to digital converters, or ADCs, are essential components in modern electronic   devices. They are used to convert analog signals, such as sound or light, into digital data that can be processed by computers and other digital devices. ADCs are used in a wide range of applications, from audio recording and playback to medical imaging and industrial control systems.
　　ADCs work by converting analog signals into a series of digital values (see Figure 5-3). The process of converting analog signals into digital data is a three-step process, consisting of   sampling, quantization, and encoding. 

Figure 5-3  Analog to Digital Converter
4.1?Sampling
　　The first step in the conversion process is sampling. Sampling involves taking periodic samples of the analog signal at a fixed rate. The rate of sampling is known as the sampling rate, and it is measured in samples per second. The higher the sampling rate, the more samples are taken, and the more accurate the digital representation of the analog signal.
　　Sampling is a critical step in the conversion process because it determines the accuracy of the digital representation of the analog signal. If the sampling rate is too low, the digital representation of the analog signal will be inaccurate, and important details of the signal may be lost.
4.2?Quantization
　　The second step in the conversion process is quantization. Quantization involves assigning a digital value to each sample of the analog signal. The process of quantization involves dividing the input voltage range into a finite number of discrete steps. Each step is assigned a digital value, which represents the voltage of the input signal at that point in time.[2] The more steps in the quantization process, the more accurate the digital representation of the analog signal.
　　Quantization ensures that the digital representation of the analog signal is accurate and   precise. Without quantization, the digital representation of the analog signal would be continuous, and it would be impossible to store or process the signal using digital devices.
4.3?Encoding
　　The final step in the conversion process is encoding. Encoding involves converting the   digital values produced by the quantization process into binary codes that can be stored and processed by computers and other digital devices.[3] The most common encoding method is the binary code, where each digital value is represented by a string of 1’s and 0’s.
　　Encoding allows the digital representation of the analog signal to be stored and processed by computers and other digital devices. Without encoding, the digital representation of the analog signal would be meaningless to digital devices, and it would be impossible to use the signal for any practical purpose.
5. Digital to Analog Converter (DAC)
　　A digital to analog converter (DAC) is a device that converts digital signals into analog  signals (see Figure 5-4). It is commonly used in various electronic systems, such as audio players, digital instruments, and communication devices. The process of converting a digital signal into an analog signal involves several steps. 

Figure 5-4  Digital to Analog Converter
5.1?Input digital signal
　　The DAC receives a digital signal as input. This digital signal is usually in the form of   binary data, where each bit represents a discrete value.
5.2?Sample-and-hold
　　The digital signal is first passed through a sample-and-hold circuit. This circuit samples the digital signal at regular intervals and holds each sample value until the next sample is taken. [4] This process helps to reconstruct the continuous-time analog signal from the discrete digital samples. 
5.3?Conversion
　　The sampled digital values are then fed into a digital-to-analog conversion circuit. The  purpose of the conversion circuit is to convert the discrete digital values into continuous analog voltages or currents. There are different types of DAC architectures, such as resistor ladder DACs, delta-sigma DACs, and multiplying DACs, each with its own implementation details. However, the basic principle involves using the digital input to generate a corresponding analog output.
5.4?Reconstruction filter
　　The output of the DAC, which is an analog signal, may contain some unwanted high-frequency components due to the sampling process. To remove these unwanted components, a reconstruction filter is often used. The reconstruction filter attenuates the high-frequency components and    reconstructs a smooth analog signal.
5.5?Output amplification
　　In some cases, the output signal from the DAC may need to be amplified to achieve the  desired signal level. An amplifier is used to increase the power or voltage level of the analog signal before it is sent to the output device, such as a speaker or a display.
New Words
analog 
['(n(l?(g]
n. 模拟
adj. 模拟的
digital  

['d(d((tl]
n. 数字
adj. 数字的
form 
[f((m]
n. 形式
continuous 
[k(n't(nju(s] 
adj. 连续的
function 
['f((k(n]
n. 函数；功能，作用
conversion 
[k(n'v(((n]
n. 转换，变换
behavior 
[b('he(vj(]
n. 行为；（机器等的）运转状态
amplifier 
['(mpl(fa((] 
n. 放大器；扩音器
filter 
['f(lt(]
n. 滤波器
v. 过滤，渗透
susceptible 
[s('sept(bl] 
adj. 易受影响的
noise 
[n((z]
n. 噪声，杂音
definition 
[(def('n((n]
n. 定义
susceptibility 
[s((sept('b(l(t(]
n. 敏感性
complex 
['k?mpleks] 
adj. 复杂的；复合的
manually 
['m(nj((l(]
adv. 用手地，手动地
flexibility 
[(fleks('b(l(t(] 
n. 柔韧性，机动性，灵活性
implementation 
[((mpl(men'te((n]
n. 实现
consumption 
[k(n's(mp(n]
n. 消耗，消费
observational 
[(?bz('ve(((nl]
adj. 观测的，观察的
wirelessly 
['wa((l(sly] 
adv. 无电线地
storage 
['st((r(d(] 
n. 贮存，储存
quantization 
[(kw?nt('ze(((n] 
n. 量化，数字化
encode 
[(n( k((d]
vt. 编码
periodic 
[(p((r((?d(k] 
adj. 周期的，定期的
representation 
[(repr(zen(te((n] 
n. 表示，代表，表现
inaccurate 
[(n((kj(r(t] 
adj. 不精确的，不准确的
meaningless 
[(mi(n((l(s]
adj. 无意义的，无价值的
binary 
[(ba(n(r(]
adj. 二进制的
bit 
[b(t] 
n. 位，比特（二进位制信息单位）
interval 
[((nt(vl] 
n. 间隔，区间
reconstruct 
[(ri(k(n(str(kt] 
vt. 重建，改造
high-frequency 
['ha('fri(kw(ns(]
adj. 高频率的
smooth 
[smu(?]
adj. 平滑的，光滑的
vt. 使平滑
achieve 
[((t(i(v]
v. 实现
Phrases
analog circuit
模拟电路
digital circuit
数字电路
signal process
信号处理
analog signal
模拟信号
be composed of… 
由……组成
be fed to
馈送到
active circuit 
有源电路
passive circuit
无源电路
signal waveform
信号波形
building block
组成模块
digital logic gate
数字逻辑门
be converted into
被转换为
sampling process
采样过程，抽样过程
power source
电源
input signal
输入信号
output signal
输出信号
circuit component
电路元件
processing speed
处理速度
logical operation
逻辑运算
industrial control system
工业控制系统
sampling rate 
采样率，抽样率
digital value
数字值
digital device
数字设备，数字器件
binary code
二进制代码
encoding method
编码方法
a string of
一串，一系列
audio player
音频播放器
digital instrument
数字仪器
sample-and-hold circuit
采样保持电路
reconstruction filter
重建滤波器，重构滤波器
Abbreviations
ADC (Analog to Digital Converter)
模数转换器
DAC (Digital to Analog Converter)
数模转换器
Notes
　　[1] The digital circuits can only be active circuits, which means they require an additional power source to power the circuit. 
　　本句中，which means they require an additional power source to power the circuit是一个非限定性定语从句，对主句进行补充说明。
　　本句意为：数字电路只能是有源电路，这意味着它们需要额外的电源来为电路供电。  
　　[2] Each step is assigned a digital value, which represents the voltage of the input signal at that point in time. 
　　本句中，which represents the voltage of the input signal at that point in time是一个非限定性定语从句，对a digital value进行补充说明。
　　本句意为：每个步骤都分配一个数字值，它代表该时间点输入信号的电压。
　　[3] Encoding involves converting the digital values produced by the quantization process into binary codes that can be stored and processed by computers and other digital devices.
　　本句中，produced by the quantization process是一个过去分词短语，作定语，修饰和限定the digital values。that can be stored and processed by computers and other digital devices是一个定语从句，修饰和限定binary codes。
　　本句意为：编码指将量化过程产生的数字值转换为可以由计算机和其他数字设备存储和处理的二进制代码。
　　[4] This circuit samples the digital signal at regular intervals and holds each sample value until the next sample is taken. 
　　本句中，This circuit是主语，samples the digital signal at regular intervals and holds each sample value是and连接的并列谓语。until the next sample is taken是时间状语。samples是动词sample的单数第三人称形式，后面的两个sample是名词。
　　本句意为：该电路定期对数字信号进行采样，并保存每个采样值，直到进行下一个    采样。 
Exercises
【Ex.1】根据课文内容，回答以下问题。
1. What is an analog circuit? What are analog circuits composed of ?


2. What is a digital circuit?


3. What are the types of analog circuits and digital circuits respectively?


4. How do ADCs work? What are the three steps of doing it mentioned in the passage? 


5. How many steps does the process of converting a digital signal into an analog signal involve? What are they?

 
【Ex.2】根据下面的英文解释，写出相应的英文词汇。
英 文 解 释
词    汇
a type of electronic circuit that uses continuous signals (analog signals) to represent information

a type of electronic circuit that use discrete signals (digital signals) to represent   information 

a system that converts a?digital signal?into an?analog signal

an electronic device that increases the?voltage,?current, or?power?of a?signal

                                                                                   续表    
英 文 解 释
词    汇
a device or process that removes some unwanted components or features from a signal

communication using radio waves, light, or other methods without wires 

a process through which digital data is saved within a data storage device by means of computing technology

the process of converting data into a format required for a number of information processing needs

a numeric system which uses two numerals, 0 and 1, to represent all real numbers

the smallest unit of data that a computer can process and store 

　　
【Ex.3】把下列句子翻译成中文。
1. The signal will be converted into digital code. 
 

2. No computer can imitate the complex functions of the human brain. 
 
 
3. Amplifier array provides a new perspective for low power consumption design. 
  

4. Filters do not remove all contaminants from water. 
 

5. Software business process needs higher flexibility and adaptability. 
 

6. Any device that’s built to receive a wireless signal at a specific frequency can be overwhelmed by a stronger signal coming in on the same frequency. 
 
  
7. His task is to ensure the fair use and storage of personal information held on computer. 
 
 
8. We compared the human mind to a computer which actively seeks information to process,    encodes it and stores it for future use. 
 

9. The instructions are translated into binary code, a form that computers can easily handle. 
 
 
10. To give a definition of a word is more difficult than to give an illustration of its use. 
 
　
【Ex.4】把下列短文翻译成中文。
　　Industrial control system (ICS)?is a collective term used to describe different types of   control systems and associated instrumentation, which include the devices, systems, networks, and controls used to operate and/or automate industrial processes. Depending on the industry, each ICS functions differently and are built to electronically manage tasks efficiently. Today the devices and protocols used in an ICS are used in nearly every industrial sector and critical        infrastructure such as the manufacturing, transportation, energy, and water treatment industries. There are several types of ICSs, the most common of which are?supervisory control and data       acquisition (SCADA) systems, and?distributed control systems (DCS).
　　
【Ex.5】通过Internet查找资料，借助电子词典、辅助翻译软件及AI工具，给出模拟电路和数字电路的若干应用实例，并附上收集资料的网址。通过E-mail发送给老师，或按照教学要求在网上课堂提交。
Text B
Digital Circuit Elements
1. CMOS Element and Watch Switching
　　The complementary MOSFET scheme (or CMOS) started the second revolution in    computational machines. The limits of speed and density were conquered by the move to   semiconductors and very large scale integration, but the power consumption and circuit cooling demands of bipolar transistors packed at extreme densities were formidable problems. The  problem was that the transistors were always “ON” (in other words drawing current and        dissipating energy). CMOS circumvents this problem and allows bits to be stored without       constant power consumption. A schematic of the CMOS inverter is given in the figure below (see Figure 5-5). The device dissipates energy only when it is switched from high to low or back. Quiescent operation in either the high or the low state dissipates essentially no power. So cooling the circuit is much easier, and supplying power is much less of a problem. If you don’t believe me, just ask your calculator, digital watch or your laptop.
　　Connect VDD = +5V and ground to the CD4007 pins as depicted below using only one set of transistors. For example, pin 10 = VI, pin 11 = VDD, pin 9 = GND and pin 12 = VO. Connect a 500? resistor between VDD and pin 11 for better performance.
　　Slowly ramp the input voltage from zero up to 3.5V. At some point the output should switch