Chapter 1, Problem 1.24P

The zero−bias capacitance of a silicon pn junction diode is $C_{jo}=0.02\text{pF}$ and the built−in potential is $V_{bi}=0.80\text{V}$ . The diode is reverse biased through a $47-\text{k}\Omega$ resistor and a voltage source. (a) For $t<0$ , the applied voltage is 5 V and, at $t=0$ , the applied voltage drops to zero volts. Estimate the time it takes for the diode voltage to change from 5 V to 1.5 V. (As an approximation, use the average diode capacitance between the two voltage levels.) (b) Repeat part (a) for an input voltage change from 0 V to 5 V and a diode voltage change from 0 V to 3.5 V. (Use the average diode capacitance between these two voltage levels.)