晶体管特性文献翻译综述

1、晶体管特性第一章中已经指出，晶体管能够放大电流。因此，晶体管在电子线路中应用很广，例如音频放大器，助听器，扩音机放大器，无线电接收机和电视接收机，测量仪表和工业控制。另外，晶体管也可以用作“电子开关，它可使电流通路或者呈现高电阻或者 呈现低电阻。这就是晶体管有可 能在计算机电路和控制系统中获得广泛应用。对每一项应用都必须进行细致的电路设计，在能够系统地进行设计工作之前，应对晶体管这一电路元件的特性有个详尽的了解，知道什么是最正确工作电压和电流，对信号的阻抗有多大，晶体管的放大倍数有多大，什么是晶体管输出端内阻抗等等。这些特性资料可从各类晶体管有关数据中获得，这些数据由制造厂商提供，印成“数据表

2、发行,使晶体管使用者能根据此进行初步设计，而不必自行量测。首要的问题是取得晶体管电压电流关系曲线。通常要提供出两组曲线；发射结正向电压电流特性曲线，通常称为发射极特性曲线或输入特性曲线；以及集电结反向电压电流曲线，通常称为集电极特性曲线或输出特性曲线。1基特性曲线首先研究共基极电路，图1所示为发射极基极正向特性曲线，它描述了发射极电流如何随发射极基极电压从零正向增高而增大。图上所示的特性曲线是小型锗管的典型曲线。由图可看出，最初电流随电压增高而增加，但增加的幅度很小。在这期间，外加电压逐渐克服pn结的势垒。势垒一旦被中和，电流就迅速增加。发射极电流皿现在来研究发射极电流变化时集电极电路出现的情

3、况。首先，发射极电流为零时集电极基极特性如图2中Ie=O的曲线所示射结电流增加到1毫安图1中的A点，并使之维持不变。我们看到，几乎全部发射极电流都传送到集电极，通过集电极的电流量与集电极电压的上下无关。这样,集电极电压电流特性曲线就成了图2中Ie=2, 3,4和5毫安时的集电极曲线 B,C, D和E。集电极压发生大幅度变化时，电流变化很小。特性曲线几乎处于水平位置这一性质突出了高输出电阻这一特性，因而集电极电A* 1ET严匚E=3D)DE=4E-V-4-3'2-1图2集电极基压特性由图中可以看出，甚至在集电极电压为零时仍然存在集电极电流。这是因为基极电流在通过基区电阻时在集电极基极回路

4、中产生一小电势差，从而在集电极两端形成很小的反向偏压。要使集电极电流减为零，就需要外加一很小的正向集电极电压J2如图2所示。就是这样处理的。图2中集电极特性曲线画在第三象限，以使人们注意到集电极反向偏置。现在一般把它画在第一象限，如图3所示，这在某种程度上是由于热离子管的输出特性曲线本身&>&(?护|E=2IE J7Ie=0200 10集电极电压 V图3集电极特性曲线2共基极放大器的相位关系基极发射极回路是正向偏置。以 pnp晶体管为例，它的发射极与基极相比为正。信号正向半周与Vee串联连接时，发射极比以前更正，使发射极基极电流增大。在晶体管中，发射极基极电流的增大使集电

5、极电流相应增加。由于Rl中的电流方向朝上，此电阻器上端与它的下端相比拟就比以前更正了。因此，正向半周输入信号引出正向半周输出信号。这就是说共基极晶体管放大器没有倒相问题。护.-沪P输厂亠宀 输出I>xM “A'农emm -Vcc图4共基极放大器的倒位关系在许多类型的多级放大器、振荡器和电视用视频放大器中，相位关系是考虑的重要问题。对今后的应用来说，重要的是要记住我们如何判断倒相与否的方法。3单电源共基极电路N-P-NRL共基极电路的设计通常防止使用发射极电池Vee。要做到这一点，只需加上一基极电阻Rb,并使此电阻的低端成为输入和输出回路两者的公共端。 此电路除了省去发 射极电池外

6、， 还使一个输入端和一个输出端处于低电位。这样，输入和输出两个回路现在都有一个公共的参考电位低电位。流过 Rb的小股电流Ico和地连接，它相对于基 极是负的这是npn晶体管。因 而不用电池就获得了较小的正向偏压。偏置电阻Rb可以旁路，这样在可能出现交流信号时 Rb的电压降仍保持不变。4共发射极特性曲线共发射极连接时可得出与共基极连接时相类似的特性曲线。首先是输入特性曲线，它说明基极电流随发射极基极结两端电压正向升高而变化的情况，如图6所示；其次是输出特性曲线，它说明集电极电流随不同基极电流下的集电极电压变化已定 的情况下， 基极电流变化比发射极电流变化小。图 7的输出特性曲线和共基极特性曲线

7、很相似，只是电流曲 线有明显的坡度，即电流随电压而增大。这说明它的输出电阻比基 极电路低，但它仍然是相当高的。/L7 此外，集电极电压为零时集电极电流也为零，这是因为基极电流所形成的电势并没有出现在集电极反射极回路。5集电极电压V152010图72N78输出特性曲线5集电极曲线的应用当你观察集电极曲线时，首先映入眼中使你感兴趣的是电流并不随集电极电压的变化而急剧增大。它是一组十分近似于水平的直线，特别在基极电流很低的区域；即使在 基极电流较 高的区域，坡度也很平缓的。我们可以说：在制造厂商所推荐的区域范围内 ,晶体管的集电极电流 相对独立于集电极电压。图8 lb Ic曲线与之相反，在集电极电势

8、恒定的条件下，基极电流稍有变化就可使用集电极电流发生较大的变化。基极电流作等值增长时，集电极电流是否相应地等值上升呢？为了弄清这一点，我们选定一集电极电势，譬如说5伏，然后沿这条5伏线上升。注意观察基极电流每增加25毫安时集电极电流的变化情况。为帮助你估算集电极电流的变化量，我们绘制了集电极电势为5伏的lb Ic曲线。虽然这条曲线并不完全是一条直线，但它确实很近似于直线，如果晶体管用于例如音频放大电路，我们就可以说：如果lb的变化局限在相当小的范围内，集电极电流就随lb作线性变化。这一提法可进一步解释如下：如馈入基极的输入电流是弱音频电流，那么集电极回路的电流变化比输入电流的变化大，但其波形保

9、持不变。这样，我们得到一种度量我们对这类晶体管所能要求 的保真度的方法，或者反过来说，度量晶体管固有畸变的方法。输出无畸变-* 传输输入 畸变传输、 JF| |输入图9晶体管畸变曲线只要lb Ic曲线是条直线，其固有畸变就为零。曲线的曲率越大，晶体管本身所造成的畸变越严重 可能出现与晶体管固有特性无关的畸变。4nA=0.125mA一一一3mA2 9_ ,_0.1mA5V集电极电压图10 Ic的改变影响lb的改变我们可利用集电极特性曲线或者 lb Ic曲线在几秒钟内即可估算出晶体管的 B值。晶体管集 电极特性一般可在制造厂商的参数表中取得。让我们利用它来校核晶体管2N78的？值，即常说的所谓的基

10、极电流增益。晶体管2N78通常在5伏集电极电位下工作，我们先找出5伏线，然后沿此线选出 基极电流变化的一般区域范围内，例如从 100微安到125微安。利用我们已经知道的等 式B = Ic/A lb,取lb从100微安到125微安的变化为 lb,它等于25微安。然后，我 们可注意到在lb的变换范_35-290.6卩=0.025 = 0.025 =24围内lc从2.9毫安变为3.5毫安。将这些值代入等式就得到：6单电池共发射极电路关于这个电路，让我们先回忆第三节双电池共基极放大器改成单电池电路的局部。你可能会发现，为了提供所需要的偏置电位，需要在基极回路上外加一电阻和电容。电阻R.使基极相对于发射

11、极正向偏置和集电极反向偏置都具有正确的极性。如果我们进一步分析双电池共基极电路，显然可知，需要外加偏压元件的原因在于发发射极和集电极电流的流动方向。我们用 pnp晶体管为例，可知le和lc在接向基极的 公共引线中流动方 向相反。由于用一个电池，不管放在电路的哪个局部，要在一个元件中产生两股方向相反的电流是决不可能的，所以为了建立正常的偏置电位，借助于人为的辅助元件即偏置电阻是完全必要的。1 H11+ +1111Vrp Vcc图11双电池共发射极电路现在我们来分析双电池共发射极电路。Vee使电子流向通过 Ri 或通过信号源本身，假设信号源是连续直流的和基极到发射极，再向下经过公共导线回到电池的正

12、端，女口深色箭头所示。Vee使电子流向通过Fl和集电极到发射极，再向下经过公共连接线回到电池的正端，如浅色箭头所示。由此可知，从发射极到两组电池正极结点的公共导线中电流的流向相同。这就很容易用一组电池来完成原来两组电池的工作。不管我们把电池接到那里，一定要记住，pnp晶体管的基极相对于发射极应是负的，但负的程度不如集电极。信输Vpr Vcc图12发射极和集电极电流的流动同向图13单电池基极发射极放大电路实际上去掉第二组电池很容易，这不能不使我们感到奇怪，为什么在共发射极电路中曾经使用过两组电池。我们只注意到 Vee和Vcc相对于发射极都是负的。全面检查线 路的连接，我们很 快就可看出，集电极电

13、流的通路与过去完全相同；从电池的负端通过集电极，离开发射极，又回到正端。与此同时，同一电池按深色箭头指示的方向把电流虽然可能很小送入基极回路。这股电流的流动和采用两组电池时的情况完全相同。剩下要作的只是选择适当的电阻值，使基极电压大小适宜。由于Ri阻值大小在很大程度上取决于晶体管类型、Vcc的电势和环境温度，所以我们无法提供某一定值。晶体管2N78在标准中频电路室温下的 Ri典型阻值为 10,000 欧姆左右。来自?晶体管原理?附：英文原文Transistor CharacteristicsIt has been shown in the previous chapter that the t

14、ransistor is cable of amplifying electric currents. As a result, it can be used for many applications in electronic circuits, such as audio amplifiers, hearing aids, pubic address amplifiers, radio and television receivers, in strume ntati on and in dustrial con trol. Also, the tran sistor can be us

15、ed as an "electro nic switch ", that is it can prese nt either a high or a low resista nee to the passage of curre nt. This ope ns up the possibility of wide use in computer circuits and control systems.For each application careful circuit design work must be carried out. Before this can b

16、e done systematically, it is necessary to have detailed knowledge of the characteristics of the characteristics of the transistor as a circuit element, that is, to know what is the best operating voltage and current, what impedance is presented to the signal, what amplification the transistor will g

17、ive, what is the internal impedance of the transistor at the output, and so on. Data from which in formatio n of this n ature can be obta ined is prepared by the manu facturer on each type of tran sistor and published as prelim inarydatadesig n without hav ing to make measureme nts himself.shtb etss

18、e caHoFirst, it is importa nt to derive groups of voltage-curre nt relati on ships for the tran sistor. Two sets of curves are no rmally prese nted, the forward voltage-curre nt characteristics of the emitter junction, referred to as the emitter characteristics curves of the collector junction, call

19、ed the collector characteristics or the output characteristics.1 Common Base CharacteristicsCon sideri ng first the com mon base arran geme nt, Fig. 1 shows the emitter to base forward characteristic, that is, how the emitter curre nt in creaser as the emitter to base voltage is in creased positivel

20、y from zero. The characteristic show n is typical of a small germa nium tran sistor. It will be see n that at first the curre nt in creases only very slightly as the voltage is increased.During this region the applied voltage is overcoming the potential barrier of the junction. Once the barrier has

21、bee n n eutralized, the curre nt in creases rapidly.EMITTER-BASE VOLTAGE, VOLTS Fig 1 In put charactcrijric of com mon ba?c circuit.Now consider what happens in the collector circuit when the emitter current is varied. At first, with zero emitter curre nt, the collector to base characteristic is sho

22、w n as the cure for in Fig. 2. This is similar to the reverse characteristic of a pn junction shown previously in Fig The small current is known as the leakage current of the collector junction. Now let the emitter curre nt be in creased to 1 mA point A in Fig. 1 and held con sta nt at that value. W

23、e have see n that n early all of the emitter current passes to the collector, the amount of current crossing the collector junction not being depe ndent on the collector voltage. Thus theAJr e= iE0Ci严DLE)iE=scollector voltage current characteristic will now be curve A fore=1 in Fig. 2.Similarly, as

24、the emitter curre nLs in creased in further steps collector curves B,C,D and E LECTOare obtained for emitter current I e=2,3,4 and 5 mA. The almost horizontal nature of the collector characteristics emphasizes the high output resista nee, a large cha nge of collector voltage produc ing only a very s

25、mall cha nge of curre nt.It will be seen that the collector current is maintained even at zero collector voltage. Thisis because the base curre n t, i n flow ing out through the resista nee of the base regi on, sets up a small pote n tial which appears in the collector-base circuit, and con stitutes

26、 a small reverse bias across the collector junction. To reduce the collector curre nt to zero it is n ecessary to apply arIe=jfrfsmall forward collector voltage as shown in Fig. 2.In Fig. 2 the collector chafactBHst杞s°have bee n show甲 ilh the third quadra nt as a remin dera coitit no ti-base ti

27、amsistor ain plifieithat the collector ju n ctio n is biased in the reverse direct ion. It is now customary to prese nt them in the first quadra nt as show n in Fig. 3, to some exte nt because the output characteristics ofHMHaME Ho-L3mthermio n ic valves were alw/ays draw n in this way.OUTPUT2 Hase

28、Relati ons in a Common-Base AmplifierF-ST-FR|dXCOLLEcTQRFig? Collctor<VOLATAGE, VOLTStic, coi mnon basJiccui+ThTil卜INPUT._.The base-emitter circuit is forward-biased. In the case of the pnp tran sistor used as an example, this means that the emitter is more positive tha n the base. Whe n a positi

29、ve-go ing half-cycle is now inserted in series with V ee ,the emitter becomes more positive than before, increas ing the emitter-base curre nt. In a tran sistor, an in crease of emitter-base curre nt produces a corresp onding in crease of collector curre nt. Since the direct ion of curre nt flow is

30、upward in Rl,the top terminal of this resistor must become more positive than it was before with respect to the bottom termi nal. Hence a positive-go ing in put half-cycle gives rise to a positive-go ing output half-cycle. This means that there is no phase inv ersi on in the com mon base tran sistor

31、 amplifier.Phase relati ons are importa nt con siderati ons in many types of multistage amplifiers .In oscillators, and in video amplifiers for television. It is important to remember how we determ ine whether phase inv ersi on does or does not occur for future use.3 Sin gle-battery Common-base Circ

32、uitFigj The cottirti on-base circuitVrrA com mon-base circuit is no rmally desig ned to do away with the n eed for an emitter battery V ee To do this we n eed merely add a base resistor(R and make the lower term inal of this resistor com mon to both in put and output circuits. In additi on to doing

33、away with the emitter battery, this circuit makes it possible to main ta in one in put and one output term inal at ground pote n tial . There is now a com mon refere nee pote n tial(gro und) for both in put and output. The small leakage current I co flowing through R b places the base at a slightly

34、higher positive pote ntial tha n ground. Since the emitter is conn ected to ground through R e, this eleme nt must be n egative with respect to the base(this is an npn transistor). Thus, the small amount of for-ward-bias is obta ined without the n eed for a battery. The bias resistor R b may be bypa

35、ssed to maintain the voltage drop across it constant, despite the possible presence of alter nat ing sig nal curre nts.4 Com mon Emitter CharacteristicsWith the com mon emitter conn ecti on, similar characteristics can be prepared. First, the input characteristic, which shows how the base curre nt v

36、aries as the voltage across the emitter-base jun cti on is in creased in the forward direct ion, as show n in Fig. 7. It will be see n152tDD5D- D5 H 115 乩 2 Q. 25BASE VOLATAGE, VOLTS?oaFigg Iput characteristic of com mon emitter ciicuitfrom Fig. 6 that the in put resista nee is higher tha n for the

37、com mon base arran geme nt, the cha nge of base curre nt being smaller tha n the cha nge of emitter curre nt for a give n cha nge of emitter to base voltage .The output characteristics in Fig. 7 are similar to the com mon base characteristics except that there is now a noticeable slope on the curren

38、t lines, the current in creas ing with voltage. This in dicates that the output resista nce is lower tha n in the com mon base arrangement; but nevertheless it is still high. Also, the collector current is now zero for zero collector voltage since the pote n tial produced by the base curre nt does n

39、ot appear in the collector to emitter circuit.COLLECTOR VOLATAGE, Y OLTSF1E7 Collctar charat eristic, conunon 亡 rtiittM circuit5 Usi ng the Collector CurvesOne of the first in terest ing things that strikes you as you look at the collector curves is that the current does not rise very rapidly with c

40、hangesof collector voltage. Notice how horiz on tai the graph lines are, especially whe n the base curre nt is low. Eve n for higher base curre n ts, the slopes are very shallow. We can say it this way: over the range recomme n ded by the manufacturer, the collector current of a transistor is relati

41、vely independent of the collectorvoltage.On the other hand, a small cha nge of base curre nt always produces a relatively large cha nge in collector curre n t, if the collector pote n tial is maintained con sta nt. Does the collector curre nt rise in equal steps for equal in creme nts of base curre

42、nt? To see this, choose a certa inVc 二5V/collector potential, say 5 volts, then follow the 5-volt line upward and note how the current changes, we have draw n b Ic curve for a collector pote ntial of 5 volts.E54Although this curve is not a perfect straight line, it certainly does approach it closely

43、. Of the transistor is used in an audio amplifier circuit, for example, we might then say: If the range of variati on of I b is held within reas on ably small limits, the collector curre nt varies lin early with it.a SD IDO 15D 也口 25n 3DQBASE CUTTENT8 Ib-Ic curve for 2N7S tran sistor with Vc at 5 vo

44、lts.This may be in terpreted as follows: if the in put curre nt to the base is a weak audio current, the current variations in the collector circuit will be large but will have the same waveform. Thus, we arrive at a measure of the fidelity or, conv ersely, the in here nt distortio n that we may exp

45、ect from a transistor of this type. As long as the b Ic curve is a straight line, the in here nt distortio n will be zero. The greater the curvature of the graph, the greater will be the distortion that can be attributed to the transistor itself.kamsistorOUTPUTINPUTtramsistorFig 9 氏 curved iiamsisto

46、r charate nsticmay in troduce distrotio nAll of the forego ing presupposesthat the circuit comp onents have bee n selected to produce the proper bias for the specific tran sistor used. If this is not the case, distorti on may occur that has no conn ecti on with the in here nt characteristics of the

47、tran sistor.COLLECTOR VOLATAGE, VOLTS3mAD. 125mA 今巴&b二0 25mA 6 1mAFig 10 A small part of the Collctor charate nsticEither the collector characteristic curves or the lbIc curve may be used to estimate thebeta of a tran sistor in just a few sec on ds. Since the collector characteristics are those

48、gen erallyfound in manu facturers' rati ng sheets, suppose we use these to check the beta, or base curre ntgain as it is ofte n called, of the 2N78.Since this transistor normally operates at a collector potential of 5 volts, we first locate the5-volt line. Then we select an average regi on of ba

49、se curre nt cha nge along this line, say from100 microamperes to 125 microamperes. Using our kno wledge that beta = Ic/ lb ,we can takethe change of I b from 100 卩 A to 125 卩 A for a total of Ib=25 卩 A . We then note that I c goes from 2.9 ma to 3.5 ma over this range of I b .Substitut ing these val

50、ues in the equati on we have: 3.5-2.90.6P 0.0250.025=246 The Sin gle-Battery Com mon-Emitter CircuitINPUTDISTORTIONAt this poin t, let us refer back to where we con verted the two-battery com mon-base amplifier into a single-battery circuit. You will find that it was necessaryto add a special resist

51、ance and capacitor in the base circuit to provide the required biasing potentials. That is, R b permits the base to have the correct polarity with respect to the emitter(forward bias) and with respect to the collector (reverse bias).If we an alyze the two-battery com mon-base circuit further, it is

52、appare nt that the reas on for the need of an extra biasing component lies in the directions of flow of the emitter and collector currents. Using a pnp transistor as an example (the npn is analyzed the same way except that all curre nt direct ions are reversed), we see tha e and Ic flow in opposite

53、direct ions in the com mon lead going to the base. Since one battery, placed any where at all in the circuit, could n ever produce two oppositely-directed curre nts in a com mon eleme nt, it is n ecessary to create the correct bias potentials by means of an artificial aid the bias resistor.Now let u

54、s an alyze the two-battery com mon-emitter circuit. V ee forces curre nt up through R i (or through the signal source itself if the source has d-c continuity), through the base to the emitter, the n dow nward through the com mon lead back to the positive termi nal of the battery as shown by the dark arrows. V drives