P24L_2003_Final_Exam

# P24L_2003_Final_Exam - 2 1(a A plot of the collector...

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2 1. (a) A plot of the collector current I C versus V CE of an npn Bipolar Junction Transistor (BJT), obtained from a curve tracer, shows I C increasing for increasing V CE in the active region. Briefly explain why this occurs. Also explain why the emitter of the BJT is usually highly doped. [5] (b) Consider the circuit shown in Figure 1(b). Find (i) R C (ii) R E (iii) R B (iv) V CE (v) V B Assume V BE = 0.7V and DC =80. [5] R B R C R E 12 V 7.6 V 2.4 V 2 mA Figure 1(b) (i) Consider the circuit of Figure 1(c). Given that DC is very large and V BE = 0.7V find I C , V E , V B and R 1 . [10] R C = 4.7k R 1 R 2 = 5.6 k R E = 1.2 k V CC = +18 V V C = 12V V E V B Cont’d … Figure 1(c)

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3 2. (a) Using diagrams where necessary describe the operation of an n-channel Junction Field Effect Transistor (JFET) operating with a constant drain-to-source voltage V DS and an increasing gate-to-source voltage V GS . How can the JFET be employed in this mode? [8] (b) Briefly describe how a JFET amplifies a small ac signal at its input. [2]
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P24L_2003_Final_Exam - 2 1(a A plot of the collector...

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