Chapter 3 Transistors and Integrated Circuits BIPOLARJUNCTIONTRANSISTOR BJT
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 i. E i. C i. B
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 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. • g almost unity i. E 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. • i. C consist of i. E and a very small current due to thermally generated minority carrier ICBO i. C = -ai. E + ICBO 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 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 i. E = - 5 m. A, i. C = - ai. E @ + 5 m. A. • 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 v Input and output CE Characteristics v i. B depends on VBE only. v i. B = 0 i. C = i. CEO v a = 0. 98 b = 49, v A very small increase in i. B large increase in i. C v. A very small increase in a much greater change in b. Practice Problem 6 -3
Chapter (3) Transistors and Integrated Circuits
- Slides: 10
