Suppose the BJT of Fig. P6.53 has F 5 2 ns, Cje0 5 5 pF, e 5 0.8 V, me 5 0.33, Cjc0 5 1 pF, c 5 0.75 V, mc 5 0.33, VBE(EOC) 5 0.6 V, and VCE(EOS) 5 0.2 V. Moreover, let VCC 5 2VBB 5 5V, R1 5 3 kV, R2...

Suppose the BJT of Fig. P6.53 has F 5 2 ns, Cje0 5 5 pF, e 5 0.8 V, me 5 0.33, Cjc0 5 1 pF, c 5 0.75 V, mc 5 0.33, VBE(EOC) 5 0.6 V, and VCE(EOS) 5 0.2 V. Moreover, let VCC 5 2VBB 5 5V, R1 5 3 kV, R2 5 10 kV, and RC 5 1 kV. (a) If vS in P6.53a, after having been at 0 V for a long time, is switched to 15 V, fi nd the time tEOC it takes to bring the BJT to the EOC (use the formula of Problem 6.49 to calculate Cje(eq) and Cjc(eq)). (b) We can make tEOC → 0 by adding a capacitance C as in Fig. P6.53b and adjusting it to the value CEOC that, as vS switches from 0 V to 5 V, will inject into the base the charge needed to bring the BJT right to the EOC. What is the required CEOC? (c) In fact, we can go one step further, and increase the capacitance to the value CEOS that will bring the BJT from CO, through the FA region, right to the EOS. What is the required CEOS?