急需一篇关于调制解调的英文文章，1500~2000

Question

跟我说怎么查也行，最好有翻译

Answer 1

What is the signal modulation? Has to use the signal modulation why inthe observation and control system? What is demodulates? Does thecommonly used modulation method have which how many kinds in theobservation and control system? In the precision measurement, enters the metering circuit the surveysignal which outputs besides the sensor, but also often has each kindof noise. But the sensor output signal very is generally weak, willsurvey the signal from to include the noise in the signal to separatewill be a metering circuit important task. In order to be advantageousfor the difference signal and the noise, often gives the survey signalto bestow on by the certain characteristic, this is the modulationmain function. The modulation is (is called modulation signal) with asignal to control another one (is called intelligence signal) as thecarrier signal, lets latter some characteristic parameter according toformer change. In will survey the signal modulation, and it and noiseseparation, after processing and so on enlargement, but also must fromin the signal which already modulated withdraw the reflection by theobserved value survey signal, this process was called thedemodulation. Often takes the intelligence signal in the signal modulation by a highfrequency sine signal. A sine signal has the peak-to-peak value, thefrequency, the phase three parameters, may carry on the modulation tothese three parameters, separately is called the amplitude modulation,the frequency modulation and the phase modulation. Also may use thepulse signal to make the intelligence signal. May make the modulationto the pulse signal different characteristic parameter, what is mostcommonly used is carries on the modulation to the pulse width, iscalled the pulse to adjust the width. 3-2 what is the modulation signal? What is the intelligence signal?What was has adjusted the signal? The modulation is bestows on for the survey signal by the certaincharacteristic, this characteristic by provides as the carrier signal.Often takes the carrier by a high frequency sine signal or the pulsesignal, this carrier is called the intelligence signal. With thesignal which needs to transmit changes the intelligence signal someparameter, like peak-to-peak value, frequency, phase. This uses for tochange the intelligence signal some parameter letter to be known asthe modulation signal. Must transmit in the observation and controlsystem surveys the signal, usually uses the survey signal to make themodulation signal. Yells after the modulation carrier letter hasadjusted the signal. Why 3-7 said the signal modulation is advantageous to the enhancementobservation and control system signal to noise ratio, is advantageousto sharpens its antijamming ability? Which aspects does its functionmanifest through? In the precision measurement, enters the metering circuit the surveysignal which outputs besides the sensor, but also often has each kindof noise. But the sensor output signal very is generally weak, willsurvey the signal from to include the noise in the signal to separatewill be a metering circuit important task. In order to be advantageousfor the difference signal and the noise, often gives the survey signalto bestow on by the certain characteristic, this is the modulationmain function. In will survey the signal modulation, and it and thenoise separation, after will pass through again processing and so onenlargement, but also will have from in the signal which alreadymodulated to withdraw the reflection by the observed value surveysignal, this process was called the demodulation. Through the modulation, to surveys the signal to bestow on by thecertain characteristic, causes to adjust the signal the frequency bandin take the intelligence signal frequency as in the central verynarrow scope, but the noise includes each kind of frequency, namelyapproaches to the white noise. By now was allowed to use chooses thefrequency amplifier, the filter and so on, only let take the carrierfrequency pass as in a central very narrow frequency band signal, wasallowed effectively the noise elimination. Uses the carrier frequencyto carry on the comparison as the reference signal, also may suppressis far away the reference frequency each kind of noise. 3-8 why in observation and control system frequently in sensor clearsignal modulation? In order to sharpen the survey signal antijamming ability, oftenrequested from the signal as soon as to form already was has adjustedthe signal, therefore frequently carried on the modulation in thesensor. 3-13 what is the envelope detection? Tries to state the envelopedetection the basic principle of work. From has adjusted in the signal to pick out the modulation signal theprocess to be called the demodulation or the detection. Thepeak-to-peak value modulation was lets adjust the signal thepeak-to-peak value along with the modulation signal value change,therefore the amplititude-modulated signal envelope shape wasconsistent with the modulation signal. So long as can pick out theamplititude-modulated signal the envelope curve namely to be able torealize the demodulation. This method is called the envelopedetection. From attempts in X3-10 to be allowed to see, so long as from attemptsin the amplititude-modulated signal which a shows, clips its underhalf, after then obtains attempts b to show the half-waverectification the signal (after double-wave detection also to bepossible), again passes through the low pass filter, filters the highfrequency signal, then obtains must the modulation signal, therealization demodulation. The envelope detection is the establishmentin the rectification principle foundation. 3-15 what is the sensitive detection? Why has to use the sensitivedetection? The sensitive detecting circuit is can distinguish the modulationsignal phase the detecting circuit. The envelope detection has twoquestions: One, the demodulation main process is carries on thehalf-wave or the full-wave rectification to the amplititude-modulatedsignal, is unable from the detector output distinction modulationsignal phase. If 1-3 shows in the chart uses electricity in thetransmission feeling survey work piece outline shape example, themagnetic core 3 upward and moves the similar quantity by its positionof equilibrium to under, the sensor output signal peak-to-peak valueis same, only is 180°. Is unable from the envelopedetection electric circuit output to determine the magnetic core isupward or moves to under. Second, envelope detection electric circuititself does not have the discrimination different carrier frequencythe signal ability. Regarding the different carrier frequency signalit all by the similar way to their rectification, restores themodulation signal, this meant it does not have the distinguishingsignal the ability. In order to enable the detecting circuit to havethe distinction signal phase and the frequency ability, sharpens theantijamming ability, must use the sensitive detecting circuit. 3-16 sensitive detecting circuit and is the envelope detectionelectric circuit in the function, what the performance and in theelectric circuit constitution the most main difference? The sensitive detecting circuit and the envelope detection electriccircuit is the sensitive detecting circuit can distinguish themodulation signal phase in function main difference, thusdistinguished is surveyed the change the direction, the most maindifference is the sensitive detecting circuit has in the performancethe distinction signal phase and the frequency ability, thusenhancement observation and control system antijamming ability. Lookedfrom the electric circuit structure that, the sensitive detectingcircuit main characteristic is, besides amplititude-modulated signalwhich must demodulate, but also must input a reference signal. Had thereference signal to be allowed to use it to distinguish the inputsignal the phase and the frequency. The reference signal should withthe amplititude-modulated signal which must demodulate have thesimilar frequency, uses the intelligence signal to make the referencesignal to be able to satisfy this condition. 3-20 explains with examples the sensitive detecting circuit inobservation and control system application. The chart 3-25 shows in the inductance micrometer dial electriccircuit to use the sensitive detector to make its demodulationelectric circuit, sensitive detector output instruction inductivetransceiver measuring bar displacement quantity. The chart 3-26 shows in the photoelectricity microscope, the usesensitive detector chooses the frequency characteristic, when thephotoelectricity microscope aiming was measured when , in thephotoelectricity signal does not contain the reference signal the basefrequency and the signal, the sensitive detecting circuitoutputs for zero, definite microscope aiming condition. 3-23 in uses the digital frequency meter realizationfrequency-modulated signal in the demodulation, why uses the surveycycle the method, but does not use the survey frequency the method?What insufficiency uses the survey cycle the method also to have? The survey frequency has two methods: One kind is the survey in sometime interval (for example 1 second or in 0.1 second) the signalchange periodicity, namely survey frequency method. This method surveyis in this time interval average frequency, uses in to survey thesignal with difficulty the instantaneous frequency, thus uses in withdifficulty the frequency-modulated signal demodulation; Another methodbased on the survey signal cycle, according to enters the counter in asignal cycle the high frequency clock pulse number then to obtainsignal the cycle, thus determines its frequency. The latter method mayuse in the frequency-modulated signal demodulation. Its shortcoming isenters the counter the pulse number to represent the signal period, itand the frequency transformation relations are non-linear. ( 什么是信号调制？在测控系统中为什么要采用信号调制？什么是解调？在测控系统中常用的调制方法有哪几种？

在精密测量中，进入测量电路的除了传感器输出的测量信号外，还往往有各种噪声。而传感器的输出信号一般又很微弱，将测量信号从含有噪声的信号中分离出来是测量电路的一项重要任务。为了便于区别信号与噪声，往往给测量信号赋以一定特征，这就是调制的主要功用。调制就是用一个信号（称为调制信号）去控制另一作为载体的信号（称为载波信号），让后者的某一特征参数按前者变化。在将测量信号调制，并将它和噪声分离，放大等处理后，还要从已经调制的信号中提取反映被测量值的测量信号，这一过程称为解调。

在信号调制中常以一个高频正弦信号作为载波信号。一个正弦信号有幅值、频率、相位三个参数，可以对这三个参数进行调制，分别称为调幅、调频和调相。也可以用脉冲信号作载波信号。可以对脉冲信号的不同特征参数作调制，最常用的是对脉冲的宽度进行调制，称为脉冲调宽。

3-2 什么是调制信号？什么是载波信号？什么是已调信号？

调制是给测量信号赋以一定特征，这个特征由作为载体的信号提供。常以一个高频正弦信号或脉冲信号作为载体，这个载体称为载波信号。用需要传输的信号去改变载波信号的某一参数，如幅值、频率、相位。这个用来改变载波信号的某一参数的信号称调制信号。在测控系统中需传输的是测量信号，通常就用测量信号作调制信号。经过调制的载波信号叫已调信号。

3-7 为什么说信号调制有利于提高测控系统的信噪比，有利于提高它的抗干扰能力？它的作用通过哪些方面体现？

在精密测量中，进入测量电路的除了传感器输出的测量信号外，还往往有各种噪声。而传感器的输出信号一般又很微弱，将测量信号从含有噪声的信号中分离出来是测量电路的一项重要任务。为了便于区别信号与噪声，往往给测量信号赋以一定特征，这就是调制的主要功用。在将测量信号调制，并将它和噪声分离，再经放大等处理后，还要从已经调制的信号中提取反映被测量值的测量信号，这一过程称为解调。

通过调制，对测量信号赋以一定的特征，使已调信号的频带在以载波信号频率为中心的很窄的范围内，而噪声含有各种频率，即近乎于白噪声。这时可以利用选频放大器、滤波器等，只让以载波频率为中心的一个很窄的频带内的信号通过，就可以有效地抑制噪声。采用载波频率作为参考信号进行比较，也可抑制远离参考频率的各种噪声。

3-8 为什么在测控系统中常常在传感器中进行信号调制？

为了提高测量信号抗干扰能力，常要求从信号一形成就已经是已调信号，因此常常在传感器中进行调制。

3-13 什么是包络检波？试述包络检波的基本工作原理。

从已调信号中检出调制信号的过程称为解调或检波。幅值调制就是让已调信号的幅值随调制信号的值变化，因此调幅信号的包络线形状与调制信号一致。只要能检出调幅信号的包络线即能实现解调。这种方法称为包络检波。

从图X3-10中可以看到，只要从图a所示的调幅信号中，截去它的下半部，即可获得图b所示半波检波后的信号 (经全波检波也可)，再经低通滤波，滤除高频信号，即可获得所需调制信号，实现解调。包络检波就是建立在整流的原理基础上的。

3-15 什么是相敏检波？为什么要采用相敏检波？

相敏检波电路是能够鉴别调制信号相位的检波电路。包络检波有两个问题：一是解调的主要过程是对调幅信号进行半波或全波整流，无法从检波器的输出鉴别调制信号的相位。如在图1-3所示用电感传感器测量工件轮廓形状的例子中，磁芯3由它的平衡位置向上和向下移动同样的量，传感器的输出信号幅值相同，只是相位差180°。从包络检波电路的输出无法确定磁芯向上或向下移动。第二，包络检波电路本身不具有区分不同载波频率的信号的能力。对于不同载波频率的信号它都以同样方式对它们整流，以恢复调制信号，这就是说它不具有鉴别信号的能力。为了使检波电路具有判别信号相位和频率的能力，提高抗干扰能力，需采用相敏检波电路。

3-16 相敏检波电路与包络检波电路在功能、性能与在电路构成上最主要的区别是什么？

相敏检波电路与包络检波电路在功能上的主要的区别是相敏检波电路能够鉴别调制信号相位，从而判别被测量变化的方向、在性能上最主要的区别是相敏检波电路具有判别信号相位和频率的能力，从而提高测控系统的抗干扰能力。从电路结构上看，相敏检波电路的主要特点是，除了所需解调的调幅信号外，还要输入一个参考信号。有了参考信号就可以用它来鉴别输入信号的相位和频率。参考信号应与所需解调的调幅信号具有同样的频率，采用载波信号作参考信号就能满足这一条件。

3-20 举例说明相敏检波电路在测控系统中的应用。

图3-25所示电感测微仪电路中采用相敏检波器作它的解调电路，相敏检波器的输出指示电感传感器测杆的偏移量。

图3-26所示光电显微镜中，利用相敏检波器的选频特性，当光电显微镜瞄准被测刻线时，光电信号中不含参考信号的基波频率和奇次谐波信号，相敏检波电路输出为零，确定显微镜的瞄准状态。

3-23 在用数字式频率计实现调频信号的解调中，为什么采用测量周期的方法， 而不用测量频率的方法？采用测量周期的方法又有什么不足？

测量频率有两种方法：一种是测量在某一时段内（例如1秒或0.1秒内）信号变化的周期数，即测量频率的方法。这种方法测量的是这一时段内的平均频率，难以用于测量信号的瞬时频率，从而难以用于调频信号的解调；另一种方法基于测量信号的周期，根据在信号的一个周期内进入计数器的高频时钟脉冲数即可测得信号的周期，从而确定它的频率。后一种方法可用于调频信号的解调。它的缺点是进入计数器的脉冲数代表信号周期，它与频率间的转换关系是非线性的。