1. 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.

2. 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

3. 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.

4. 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 0.999 where a typical value is 0.98. 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

5. 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

6. 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

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

8. Chapter (3) Transistors and Integrated Circuits

9. 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

10. Chapter (3) Transistors and Integrated Circuits