ABSTRACT
Electronic logic is also known as binary logic. This reflects the fact that only two values are used. These are called ‘1’ and ‘0’ and are electronically represented by two voltage levels. The original transistorized logic circuit consisted of a simple amplifier which was allowed to go into saturation. The value h FE describes the current gain of a common emitter transistor, but if more current is forced into the base so that the collector circuit cannot supply the supposedly required h FE × /B then the transistor is said to be saturated. in this state the collector-emitter voltage falls to somewhere in the range of 50–1 20 mV. The transistor is said to be fully ON. In this mode, it is used to switch on other systems. This is just the basis of a large family of logic devices which discriminate between two voltages LOW and HIGH. The gap between a voltage being allocated the tag ‘0’ and the tag ‘1’ is called the noise margin. The majority of logic devices use the nominal voltages 0 V and +5 V although modern systems operate from 0 V and 3.3 V. This reduces the power consumption and increases the speed of operation.
