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Chapter (3) Transistors and Integrated Circuits BIPOLARJUNCTIONTRANSISTOR BJT in contrast to the "unipolar" FET • Both minority and majority carries play significant roles. • Permits greater gain better highfrequency 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 VEB VCB iE iC iB Chapter (3) Transistors and Integrated Circuits Operation • The emitter junction forward biased VEB reduced the barrier at emitter electrons injection into B where they are minority carriers. • The collector junction is reverse biased VCB 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 RL insertion in C large voltage voltage amplification • Variation of the base current iB large iC current amplification • Switching operation used in digital signal processing. Chapter (3) Transistors and Integrated Circuits DC Behavior • E forward C reverse biased. • iE consist electron across np J holes from B. • g almost unity iE nearly electrons. • a 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. • iC consist of iE and a very small current due to thermally generated minority carrier ICBO iC = -aiE + ICBO I CBO e iB = -iE -iC ev / KT 1 I CBO 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 VCB small • +VCB emitter open-circuited IE = 0 C section reverse-biased junction Chapter (3) Transistors and Integrated Circuits Output Characteristics • The collector characteristic reverse bias diode iE = - 5 mA, iC = - aiE @ + 5 mA. • The slope of the curves in Fig C due to an effective increase in a as VCB increases. • a always less 1 Chapter (3) Transistors and Integrated Circuits The common base configuration is not good for practical current amplification Chapter (3) Transistors and Integrated Circuits Chapter (3) Transistors and Integrated Circuits Input and output CE Characteristics iB depends on VBE only . iB = 0 iC = iCEO a = 0.98 b = 49, A very small increase in iB large increase in iC A very small increase in a much greater change in b. Practice Problem 6-3 Chapter (3) Transistors and Integrated Circuits