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TTL数字电路按其工作状态大致可分为饱和型和非饱和型电路两种。标准型的TTL电路如图1所示,即国外的54/74系列,是典型的饱和型逻辑电路。在这种电路中,为了确保晶体管进入饱和状态,缩短晶体管的导通时间,基区必须注入大量的电流。由于大量的空穴注入晶体管的基区,使管子的BC结由反向偏置转为正向偏置,晶体管的基区和集电区内就存在着大量的少数载流子,产生了所谓饱和现象。由于这种饱和现象而产生的电荷积累,使晶体管由导通转为截止时必须设法使这个大量的少数载流子消灭或用外电路将其流出,这就需要一定的时间,这个时间叫
TTL digital circuit according to their working conditions can be divided into two types of saturated and unsaturated circuits. Standard TTL circuit shown in Figure 1, that is, foreign 54/74 series, is a typical saturated logic circuit. In this circuit, in order to ensure that the transistor into saturation, shorten the transistor on-time, the base must inject a large amount of current. Since a large number of holes are injected into the base region of the transistor to reverse the BC junction of the tube to a forward bias, there are a large number of minority carriers in the base region and the collector region of the transistor, Saturated phenomenon. Due to the accumulation of charges due to this saturation phenomenon, the transistor must be managed to extinguish this large number of minority carriers or to be discharged by an external circuit when the transistor is turned off, and this takes a certain amount of time