Digital Logic Families : Introduction , Transistor-Transistor Logic , CMOS Logic, Emitter-Coupled Logic ,Gallium Arsenide, Programmable Logic ,Programmable Array Logic and Programmable Logic Arrays
Digital Logic Families : Introduction Digital devices are constrained to two stable operating regions (usually voltage ranges) separated by a transition region through which the operating point may pass but not remain (see Fig. 7.1). Prolonged operation in the transition region does not cause harm to the devices, it simply means that the result ing outputs are unspecified. For the inverter shown in the figure, the output voltage is guaranteed to be greater than V O H as long as the input voltage is below the specified V I H . Note that the circuit is de- signed so that the input high voltage is lower than the output high voltage (vice versa for logic low volt- ages). This difference, called noise margin , permits interfering signals to corrupt the logic voltage with- in limits without producing erroneous operation. Logical conditions and binary numbers can be repre sented physically by associating one of the stable voltage ranges with one logic state or binary value and identifyi...