专业英语6-20100414.ppt

专业英语-第六讲 李聪 2010-04-14 Translation nBreakdown voltage VB depends on the doping density of a pn junction, in particular on the doping of the more lightly doped side of the junction. Fig. 8.7 shows a plot of breakdown voltage for Si diodes of different doping. It indicates the general value of the quantities, but does not account for the grading of the junction, the doping of the more heavily doped side, nor the distinction between a planar and a spherical junction. nThe mechanism of breakdown for p-n junctions with breakdown voltages less than about 4Eg/e is due to the tunneling effect. For junctions with breakdown voltages in excess of 6 Eg/e, the mechanism is caused by avalanche multiplication. At voltages between (46) Eg/e, the breakdown is due to a mixture of both avalanche and tunneling. nAlthough not large, the temperature variation of the two types of breakdown is of opposite sign. For breakdown voltages in the range of about 56 V for a Silicon diode, both avalanche- and tunnel-breakdown can occur simultaneously so that the net temperature variation is very slight. This characteristic is useful for establishing a voltage reference in some integrated circuits. Vocabulary nBreakdown voltage：击穿电压 nDiodes：二极管 nSpherical junction：球面结 nMechanism：机理 nTunneling breakdown：隧道击穿 nAvalanche multiplication：雪崩倍增 nVoltage reference ：电压基准 Breakdown voltage VB depends on the doping density of a pn junction, in particular on the doping of the more lightly doped side of the junction. 提示：depends on 翻译为与有关 翻译：击穿电压VB与pn结的掺杂浓度有关，尤其与pn结中轻掺杂 一侧的掺杂浓度有关。 Fig. 8.7 shows a plot of breakdown voltage for Si diodes of different doping. 翻译：图8.7表示了硅二极管击穿电压与掺杂浓度的关系 It indicates the general value of the quantities, but does not account for the grading of the junction, the doping of the more heavily doped side, nor the distinction between a planar and a spherical junction. 提示：general: approximate account for ：考虑 does not与nor：既不也不（呼应关系） grade: degree of slope graded junction：缓变结 linearly graded junction：线性缓变结 abrupt junction：突变结 翻译：该曲线给出了击穿电压数值的大概大小，但是未考虑到结附近杂质 的变化情况（结的杂质分布类型）、未考虑杂质较重一侧的影响、也未区 分平面结与球面结之间的差别。 Three-dimensional view of the junction curvature showing the cylindrical and spherical region The mechanism of breakdown for p-n junctions with breakdown voltages less than about 4Eg/e is due to the tunneling effect. 翻译：当pn结的击穿电压小于4Eg/e时，其击穿（机理）由遂穿效 应引起。 For junctions with breakdown voltages in excess of 6 Eg/e, the mechanism is caused by avalanche multiplication. 翻译：当pn结的击穿电压大于6Eg/e时，其击穿（机理）由雪崩倍 增效应引起。 At voltages between (46) Eg/e, the breakdown is due to a mixture of both avalanche and tunneling. 翻译：当击穿电压在46Eg/e时，其击穿（机理）则是雪崩倍增和 遂穿两种效应的混合。 注意：翻译时，注意体会同一种意思的多种说法，英文写作时非常 有用。 Although not large, the temperature variation of the two types of breakdown is of opposite sign. 提示：temperature variation指的并不是温度的变化，而是击穿电压随温度的变 化，有时也叫做“温度系数” 翻译：尽管两种击穿（电压）随温度的变化不是很明显，但两种击穿（电压）随 温度变化的趋势却是相反的。 For breakdown voltages in the range of about 56 V for a Silicon diode, both avalanche- and tunnel-breakdown can occur simultaneously so that the net temperature variation is very slight. 提示：net temperature variation指击穿电压随温度的净变化 翻译：对硅二极管来说，当击穿电压在56V时，雪崩和遂穿两种击穿将同时发 生，因此这时（击穿电压）随温度的净变化非常小。 This characteristic is useful for establishing a voltage reference in some integrated circuits. 翻译：在某些集成电路中这一特性对建立电压基准源非常有帮助 Listen then answer nWhat is breakdown voltage? nTry to describe the tunneling process of electrons in a highly doped junction. nWhere does avalanche breakdown happen? nWhat is the reason why the breakdown voltage due to the tunneling effect has a negative temperature coefficient? Part 1 nIn the ideal pn junction, a reverse-bias voltage will result in a small reverse-bias current through the device. However, the reverse-bias voltage may not increase without limit; at some particular voltage, the reverse-bias current will increase rapidly. The applied voltage at this point is called the breakdown voltage. Part 2 nTwo physical mechanisms give rise to the reverse-bias breakdown in a pn junction: the Zener effect and the avalanche effect. Zener breakdown occurs in highly doped pn junctions through a tunneling mechanism. nIn a highly doped junction, the conduction and valence bands on opposite sides of the junction are sufficiently close during reverse bias that electrons may tunnel directly from the valence band on the p side into the conduction band on the n side. Part 3 nThe avalanche breakdown process occurs when electrons or holes, moving across the space charge region, acquire sufficient energy from the electric field to create electron-hole pairs by colliding with atomic electrons within the depletion region. Part 4 nSince the energy band-gaps Eg in Si decrease with increasing temperature , the breakdown voltage in these semiconductors due to the tunneling effect has a negative temperature coefficient ; that is, the breakdown voltage decreases with increasing temperature. 1. Breakdown may result in the destruction of a device but this is not inevitable. 提示：result in是固定搭配，表示“导致”； is not inevitable谓语是否定形式，表语inevitable表示“不可避免的”， 具有否定的含义。与直接表示“可以避免的”的相比，采用这种否定加否定的方式 ，具有“强调”的作用。 翻译：击穿会导致器件的损坏，但是这并不是不可避免的。 2. Damage is caused by local melting, and if the current is held to a small value by an external resistance, or is spread over a large area by careful design and manufacture, then the temperature reached are not high enough for Silicon or SiO2 to melt, nor for impurities to diffuse out of their intended positions. 提示：第一个and连接两个并列句。 其中and后面是一个包括条件状语从句的复合句； if引导的条件状语从句中or表示“或者”，连接两个并列谓语； 翻译：损坏是由局部熔化导致的。如果采用外接电阻使电流值维持在一个较小的 数值，或者通过精心设计和制造，使电流流过较大的面积，则温度将不会升高到 使Si或者SiO2熔化的程度，也不会使杂质扩散离开其原来所在的区域。 4. So the junction capacitance is identical with that of an ordinary capacitor of the same size, shape, and permittivity as the depletion layer. 提示：that代表前面出现的capacitance（电容）； 第一个of后面的an ordinary capacitor（普通的电容器）作that的定 语； 第二个of后面到句尾作capacitor的定语。 翻译：因此，结电容与这样一个普通的电容器具有相同的电容值：该电容器 的尺寸、形状以及介电常数与耗尽层相同。 5. This fact can be put to good use in a variety of ways, since it represents a voltage-controlled capacitance. 提示：put to good use是固定搭配，表示“充分利用”； voltage-controlled是一种带逻辑主语的过去分词结构，作定语，修 饰受到控制的对象capacitance，破折号前面voltage表示动作的实施者，可 翻译为“受电压控制的电容”。 翻译：这一事实代表一种受电压控制的电容，能在多方面得到充分利用。 6. In forward bias, the excess charge stored in the neutral, or diffusion, region of the diode leads to a delay whenever an attempt is made to change the voltage across the junction. 提示：or表示“即”，不要翻译为“或者”； 注意根据上下文灵活翻译whenever。 翻译：在正向偏置情况下，二极管的中性区，即扩散区中存储有过剩载流子 电荷，因此，只要结两端的电压发生变化时，将发生延迟。 7. This small-signal capacitance can be calculated from the change Q of the excess minority carrier charge Q, stored in the neutral diffusion regions of the diode, which accompanies a small change V in the applied voltage. 提示：过去分词stored修饰Q； which引导的非限制性定语从句修饰Q。 翻译：小的外加电压变化量V将导致储存在二极管性扩散区中的过剩少子 电荷Q随之变化Q，由此可以计算小信号电容。 8. The Q charge is alternately being charged and discharged through the junction as the voltage across the junction changes. 提示：is alternately being charged and discharged是现在 进行时被动语态。 翻译：随着结电压的变化，Q电荷将交替地充电和放电。 9. The small-signal diffusion capacitance Cd is directly proportional to the current through the junction, becoming larger than the depletion layer capacitance for all reasonable forward biases. 提示：is directly proportional to表示与成正比； 由becoming组成的现在分词短语作状语； 注意根据上下文灵活翻译reasonable一词。 翻译：小信号扩散电容Cd与流过结的电流成正比，因此在通常 的正向偏置条件下，Cd大于耗尽层电容。 10. Figure 8.5 illustrates the voltage dependence, showing that with a forward bias of more than a few hundred millivolts the diffusion capacitance normally dominates, and Cj is often negligible. 提示：现在分词showing及其后面的宾语从句作状语； showing后面是由and连接的两个宾语从句，此处and 可以翻译为“而” 。 翻译：图8.5说明了（电容）随电压的变化关系。由图可见， 在正向偏置电压大于几百毫伏的范围，以扩散电容为主，而Cj 通常可以忽略不计。 Exercises：P67. 8.5 (1)When the diode is used in a circuit in which small alternating signal voltages and currents are superimposed on static (d.c.) values, the diode can be replaced for the purposes of calculating signal voltages and currents by the small-signal equivalent circuit shown in Fig. 8.6. In reverse bias, leakage effects become important in determining the