國(guó)產(chǎn)化電子鎖定放大器的設(shè)計(jì)外文翻譯

1、<p><b>　　中文1400字</b></p><p><b>　　機(jī)械與電氣工程學(xué)院</b></p><p>　　畢業(yè)設(shè)計(jì)（論文）外文翻譯</p><p>　　所在學(xué)院： 機(jī)械與電氣工程學(xué)院 </p><p>　　班 級(jí)：

2、 </p><p>　　姓 名： </p><p>　　學(xué) 號(hào)： </p><p>　　指導(dǎo)教師： </p><p>　

3、　合作導(dǎo)師： </p><p>　　2012 年 10 月 10 日</p><p><b>　　原文:</b></p><p>　　DESIGN OF AN INDIGENISED</p><p>　　ELECTRONIC LOCK-IN AMPLIFIER

4、</p><p>　　UMESH KUMAR*</p><p>　　Deptt. of Electrical Engineering, HT, New Delhi-llO016, India</p><p>　　(Received 7 April 2000; In finalform 25 April 2000)</p><p>　　An i

5、ndigenised lock-in amplifier is designed that enables the accurate measurement of signals contaminated by broad-band noise, power-line pick-up, frequency drift, or other sources of interference. It does this by means of

6、an extremely narrow band detector which has the centre of its passband locked to the frequency of the signal to be measured. Large improvements in signal-to-noise ratio are achieved.</p><p>　　Keywords: Lock-

7、in; Amplifier; Narrow band detector; Accurate signal measurement</p><p>　　I. INTRODUCTION</p><p>　　The lock-in Amplifier is analogous to a synchronous demodulator or a phase sensitive detector.

8、It is a specialized a.c. voltmeter that uses synchronous demodulation to measure signal strength or phase even under severe noise condition viz. where noise to signal ratio approaches 130dB. The instrument can be used wh

9、erever the signa </p><p>　　of interest can be synchronised with or derived from a particular</p><p>　　reference signal.</p><p>　　The output of a lock-in amplifier is a phase sensiti

10、ve d.c. voltage</p><p>　　proportional to the signal. It can be divided into four main</p><p>　　sections: A signal channel; Reference Channel; Mixer (Phase sensitive detector) and a d.c. amplifie

11、r with a low-pass filter as shown in Figure 1.</p><p>　　II. DESCRIPTION OF THE VARIOUS PARTS</p><p>　　In the signal channel, the input signal and noise is conditioned by the low-noise pre-amplif

12、iers and post-amplifier with a filter sandwiched in between. The purpose of this filter is to reduce the possibility that the mixer will overload during severe noise conditions.</p><p>　　The reference channe

13、l transforms the externally applied reference to a suitable square wave at reference frequency to drive or switch the mixer. The lock-in output is independent of the referenced amplitude. However, the output does depend

14、on the phase difference between the signal and the reference.</p><p>　　The Mixer is the main part of the lock-in amplifier. It is like an electronic reversing switch whose sense or position is determined by

15、the square drive polarity of the reference channel. The signal channel output is commutated at the reference frequency. The signal channel output consists of two equal amplitude sinusoids, one in and one out of phase wit

16、h the reference.</p><p>　　III. DESCRIPTION OF OPERATION</p><p>　　During the first half cycle, the reference drive is positive and the switch in Figure 2 is in position A. The mixer output is a p

17、ositive half-wave sinusoid during this interval.</p><p>　　During the second half wave cycle, the switch is in position B and the mixer output is still positive. Therefore, when the reference and</p>&

18、lt;p>　　sinusoidal signals are in phase at the mixer input terminals, the mixer output is a full-wave rectified sinusoid whose fundamental is twice the reference frequency and whose d.c. component is proportional to th

19、e signal of interest. When the reference drive and the signal are in quadrature, that is their phase difference is 90, there is no d.c. component.</p><p>　　Where the reference is not in phase with the signal

20、, the mixer output will not contribute any d.c. component. This is what happens to any kind of noise present in the signal.</p><p>　　In the mathematical analysis of the demodulation process, the</p>&

21、lt;p>　　mixer output m(t) can be thought of as a product of the signal</p><p>　　channel output s(t) and a-+-1 Volt peak to peak square wave.</p><p>　　With the reference represented by a Fourie

22、r series, m(+) can be</p><p>　　written as:</p><p>　　LOCK-IN AMPLIFIER 57</p><p>　　If s(t) has a frequency component in common with any of the reference components, there will be a p

23、hase sensitive d.c. component.</p><p>　　Now synchronous components share no common frequencies with</p><p>　　the reference and will not contribute d.c. components to the mixer</p><p&g

24、t;　　output. When the mixer output is passed through a low pass filter to</p><p>　　remove the a.c. fluctuations, the signal to noise ratio is enhanced in proportion to the square root of the filter time const

25、ant. Since the equivalent noise band width is determined by the low-pass filter and not the signal channel filter, band width is narrow. Figure 3 shows the actual indigenised circuit of a lock-in amplifier practically bu

26、ilt and tested in the laboratory.</p><p>　　IV. APPLICATIONS</p><p>　　Some typical applications of the lock-in amplifier are described below:</p><p>　　(a) To measure the open loop-ga

27、in of an operational amplifier</p><p>　　(Fig. 4a).</p><p>　　(b) To determine the C- V (capacitance-voltage) characteristics of a</p><p>　　MOS Transistor (Fig. 4b).</p><p&

28、gt;　　60 U. KUMAR</p><p>　　(C) To measure the amplifier cross talk (Fig. 4c).</p><p>　　(d) As a temperature controller (Fig. 4d).</p><p>　　(e) As an Eddy-current tester (Fig. 4e).<

29、;/p><p>　　(f) Also as a photometric instrument (Fig. 4f).</p><p>　　References</p><p>　　[1] Letzter, S. G., "Explore the lock-in Amplifier". Electronic Design, 22, 104-109, 11

30、</p><p>　　October, 1974.</p><p>　　[2] Macken, W. J., "Synchronous and Non-synchronous Rectification with op-amp",</p><p>　　Electronic Engineering, 45, 18-19, March, 1973.&

31、lt;/p><p>　　[3] Williams, D. R. and Lum, W. T. (1974). "Lock-in amplifier uses a single IC", Analog</p><p>　　Dialogue, 8(1), 18 19.</p><p><b>　　譯文：</b></p>

32、<p>　　國(guó)產(chǎn)化電子鎖定放大器的設(shè)計(jì)</p><p>　　UMESH KUMAR*</p><p>　　電氣工程學(xué)院，印度，新德里</p><p>　　（2000四月七日開(kāi)始制作，2000四月二十五日完成））</p><p>　　國(guó)產(chǎn)化鎖定放大器設(shè)計(jì)，能夠在較強(qiáng)干擾背景條件下，對(duì)特定頻率信號(hào)進(jìn)行有效測(cè)量，電力線路產(chǎn)生的噪聲，頻率

33、漂移的影響，或者其他干擾源。它通過(guò)極窄的頻帶檢測(cè)器，過(guò)濾掉不在頻帶范圍內(nèi)的干擾信號(hào)。就可以大大改善信號(hào)對(duì)噪聲的信噪比。</p><p>　　關(guān)鍵詞：鎖定;放大器;帶通濾波器;準(zhǔn)確的測(cè)量信號(hào)</p><p><b>　　一、引言</b></p><p>　　鎖定放大器類似于同步解調(diào)器和相敏檢波器。這是一個(gè)專門的交流電壓表，采用同步檢波測(cè)量被測(cè)信號(hào)

34、的強(qiáng)度和相位，即使在惡劣的噪聲條件使用。在被測(cè)信號(hào)和噪聲信號(hào)的比值接近130分貝。該儀器仍可用于任何被測(cè)信號(hào)，在同步信號(hào)下或者來(lái)自一個(gè)特定的參考信號(hào)中導(dǎo)出。</p><p>　　鎖定放大器的輸出是其初相位與輸出直流電壓成一定比例的信號(hào)。它可分為五個(gè)主要部分：信號(hào)通道；參考通道；相敏檢波器（PSD）、直流放大器和低通濾波器（LPF）。如圖1所示鎖定放大器工作原理圖.</p><p><

35、b>　　如圖1</b></p><p><b>　　二、各個(gè)部分描述</b></p><p>　　在信號(hào)通道中，輸入信號(hào)和噪聲先經(jīng)過(guò)低噪聲前置放大器，放大信號(hào)和噪聲。放大的信號(hào)在進(jìn)入濾波器，濾除大部分不符合的噪聲信號(hào)，最后經(jīng)過(guò)相敏檢波器將信號(hào)讀取出來(lái)。</p><p>　　參考信號(hào)通道由特定頻率的方波，在已知頻率下進(jìn)行相位的對(duì)

36、準(zhǔn)（與被測(cè)信號(hào)一致）。繼而輸入方波驅(qū)動(dòng)電子開(kāi)關(guān)。就能鎖定輸出是一定的幅值。其輸出幅值大小與被測(cè)信號(hào)和參考之間的相位差有關(guān)。</p><p>　　相敏檢波器是鎖定放大器的核心部分，相敏檢波器鑒幅又鑒相，它就像一個(gè)電子轉(zhuǎn)換開(kāi)關(guān)，它的通斷與參考通道的方波極性有關(guān)。在參考相位下，相敏檢波器的信號(hào)輸出通道輸出經(jīng)過(guò)處理的波形，其輸出波形輸出是參考信號(hào)頻率二倍的波形，其波形是兩個(gè)相等振幅完全一樣的正弦曲線。</p>

37、<p><b>　　三、操作描述</b></p><p>　　第一個(gè)半周期期間，參考驅(qū)動(dòng)波形都為正極的電路，其轉(zhuǎn)換開(kāi)關(guān)打到圖2A處的位置，其輸出正半弦波在此電路條件下進(jìn)行。</p><p>　　第二個(gè)半波周期期間，參考驅(qū)動(dòng)波形都為負(fù)極的電路，其轉(zhuǎn)換開(kāi)關(guān)打到圖2B處的位置。其輸出正半弦波在此電路條件下進(jìn)行。因此，當(dāng)參考信號(hào)和被測(cè)信號(hào)共同輸入相敏檢波器的輸入

38、端，該相敏檢波器的輸出是一個(gè)全波整流正弦其根本是兩倍的參考頻率，其直流分量與參考信號(hào)和被測(cè)信號(hào)的相位有關(guān)。當(dāng)參考信號(hào)與被測(cè)信號(hào)是正交時(shí)，這時(shí)他們的相位差是90°，沒(méi)有直流分量的輸出。</p><p><b>　　如圖2</b></p><p>　　如果不提供參考信號(hào)下就會(huì)無(wú)法驅(qū)動(dòng)相敏檢波器，相敏檢波器將不能夠工作，所以即使在任何噪聲環(huán)境下，相敏檢波器將不會(huì)有

39、任何直流分量的輸出。</p><p>　　解調(diào)過(guò)程的數(shù)學(xué)分析，相敏檢波器輸出M（T）可以被看作一個(gè)信號(hào)通道的輸出S（T）和A+ 1伏的峰-峰值的方波。用傅里葉級(jí)數(shù)表示，M（+）可以寫為：</p><p>　　如果被測(cè)信號(hào)S（t）與參考信號(hào)相位之間的相位角不等于0，那么相敏檢波器將有一個(gè)相對(duì)應(yīng)的直流分量。</p><p>　　在鎖定放大器中，假如頻率和相位不一致，將導(dǎo)

40、致相敏檢波器輸出的直流分量不正確，為了得到消除交流波動(dòng)，在相敏檢波器的輸出端，增加一個(gè)低通濾波器消除交流波動(dòng)。增強(qiáng)信噪比的平方根和濾波器時(shí)間比例常數(shù)提高信噪比。由于輸出的頻帶寬度是由低通濾波器決定的，而不是由信號(hào)輸入時(shí)的帶通濾波器決定的，帶寬很窄。圖3表示的是國(guó)產(chǎn)化鎖定放</p><p>　　大器的制作電路和實(shí)驗(yàn)室的實(shí)際使用電路圖。</p><p>　　如圖3 鎖定放大器電路</p&

41、gt;<p><b>　　如圖4</b></p><p><b>　　圖4續(xù)</b></p><p><b>　　鎖定放大器</b></p><p><b>　　圖4續(xù)</b></p><p><b>　　四、應(yīng)用</b>

42、;</p><p>　　鎖定放大器的一些典型應(yīng)用如下：</p><p>　?。╝）衡量一個(gè)運(yùn)算放大器的開(kāi)環(huán)增益（如圖4 a）。</p><p>　?。╞）確定C－V（電容電壓的MOS晶體管的特性）（如圖4 b）</p><p>　?。╟）測(cè)量放大器的串模干擾（如圖4 c）</p><p>　?。╠）作為一個(gè)溫度控制器（

43、如圖4 d）</p><p>　　(e) 作為渦流檢測(cè)儀（如圖4e）</p><p>　　(f) 也作為光度儀（如圖4 f）</p><p><b>　　參考文獻(xiàn)</b></p><p>　?。?）Letzter, S. G.“探索鎖相放大器”。電子設(shè)計(jì)，1974年10月11日。</p><p&