专业英语02.ppt

P67:The term base may well be a puzzling choice in the context of Figure 2-1(a).Actually, the term is a vestigial remnant(and practically the only remnant)of the point-contact transistor.In that device a small germanium crystal was mounted on a pedestal, and two point-contact wires(designated as emitter and collector)were positioned on top of the crystal, so that the crystal was literally the base of the structure.The central region in Figure 2-1(a) plays an electrical role analogous to that of the base region in a point-contact device. 2.1.1 Structure and Technology P68:The corresponding BJT symbol, Figure 2-1(b), was adopted very early. Once again an arrowheas is used to point from a P-type region to an N-type region, the direction of th easy conduction of conventional current through a PN junction.But only one junction-teh emitter junction is so labeled.(This is done for identification.) Once the emitter juncion has been so identified and labeled,the polarity of the collector junction becomes evident. P68:Any electrical resistance to the passage of current through this thick region is a parasitic feature of the device that one would prefer to avoid. Most BJTs today are incorporated into a integrated circuit(the microchip of the layman),defined as a useful combination of devices fabricated in and in some cased on a semiconductor single crystal.As a result, the parasitic feature of having current pass through a thick mechanical support is partly eliminated.All of the currents(in virtually all integrated circuits)are confined to a very thin region near one face of a semiconductor crystal. P69:The individual BJTs are interconnected to Perform useful circuit functions by means of a variety of methods; the result is an integrated circuit that May incorporate over 100 000 devices all fabricated Simultaneously in the same silicon crystal. P74:Figure 2-4 is a physical representation of a BJT In the “common-emitter orientation” shown first in Figure 2-1(a)