Chapter (3) Transistors and Integrated Circuits B I P O L A R J U N C T I O N T R A N S I S T O R BJT in contrast to the "unipolar" FET Both minority and majority carries play significant roles. Permits  greater gain  better high- frequency performance. Alloy Structure consist of Collector (C)  n-type chip  less than 1 mm square Base (B)  p-type  thinner than this paper Emitter n-type  alloyed to the base The result is a pair of pn junctions  separated by a base region,  npn junction transistor.

Chapter (3) Transistors and Integrated Circuits Planar Structure npn  BJT (n)  grown upon a heavily doped (n+) substrate. oxidation of the surface window  opened to diffuse impurities  (P) into the crystal to form the pn junction. A smaller window for emitter in opened to diffuse emitter region (n). Biasing Parameters BJT  C  E  B  V EB  V CB  i E  i C  i B

Chapter (3) Transistors and Integrated Circuits Operation The emitter junction  forward biased  V EB reduced the barrier at emitter  electrons injection into B where they are minority carriers. The collector junction is reverse biased  V CB increase the barrier at C B is very thin  most electron pass from E to C The net result  transfer electron from E to C. Large R L insertion in C  large voltage  voltage amplification Variation of the base current i B  large i C  current amplification Switching operation used in digital signal processing.

Chapter (3) Transistors and Integrated Circuits DC Behavior E forward  C reverse biased. i E consist  electron across np J  holes from B.   almost unity  i E  nearly electrons.  varies from 0.90 to where a typical value is Most of these electrons in B diffuse to C  B is very narrow. i C consist of  i E and a very small current due to thermally generated minority carrier I CBO i C = -  i E + I CBO i B = -i E -i C

Chapter (3) Transistors and Integrated Circuits Common - Base Characteristics CB configuration B common  input E  output C. The emitter-base section  forward-biased diode. Input Characteristics Input characteristics Fig.( b ) similar to Fig. (a)  diode characteristics The effect of V CB  small +V CB  emitter open-circuited  I E = 0  C section  reverse-biased junction

Chapter (3) Transistors and Integrated Circuits Output Characteristics The collector characteristic  reverse bias diode  i E = - 5 mA,  i C = -  i E  + 5 mA. The slope of the curves in  Fig C  due to an effective increase in  as V CB increases.   always less 1

The common base configuration is not good for practical current amplification Chapter (3) Transistors and Integrated Circuits

Chapter (3) Transistors and Integrated Circuits

Chapter (3) Transistors and Integrated Circuits  Input and output  CE Characteristics  i B  depends on V BE only.  i B = 0  i C = i CEO   = 0.98   = 49,  A very small increase in i B  large increase in i C  A very small increase in   much greater change in . Practice Problem 6-3

Chapter (3) Transistors and Integrated Circuits