emergence of the integrated chips led to increasing applications in the fast developing electronics industry. Bipolar Junction Transistor (BJT) The BJT consists of a semiconductor (silicon or germanium) crystal in which an n -type material is sandwiched between two p -type materials (PNP transistor) or . - - - - - - - - Unit electronics and Communication In a PNP transistor, base and collector will be negative with respect to emitter indicated by the middle letter N whereas base and collector will be positive in an NPN transistor indicated by the middle letter P. Note .
. Transistor circuit configurations There are three types of circuit connections for operating a transistor based on the terminal that is used in common to both input and output circuits. i) Common-Base (CB) configuration The base is common to both the input and output circuits. The schematic and circuit symbol are shown in Figure .
(a) and . (b). The input current is the emitter current I E and the output current is the collector current I C . The input signal is applied between emitter and base while the output is measured between collector and base.
– – E C I C I E I B V CB V EB N N P (a) – – V EB V CB E C I C I B I E (b) Figure . NPN transistor in common base configuration (a) Schematic circuit diagram (b) Circuit symbol Base: Base is very thin ( – m) and very lightly doped region when compared to the other two regions. Collector: The main function of collector is to collect the majority charge carriers supplied by the emitter through the base. Hence, collector is made physically larger than the other two as it has to dissipate more power.
It is modarately doped. Because of the differing size and the amount of doping, the emitter and collector cannot be interchanged. Note Transistor Biasing The application of suitable DC voltages across the transistor terminals is called biasing. The transistor biasing is done differently for different uses.
The different modes of