EECE 310 Homework 5, Fall 2011

American University of Beirut DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING EECE 310 – Electronics Fall 2011 – 2012 Due Wednesday November 2, 2011 at 9:00 am Homework 5 1. [50 points] a. [20 points] Find and plot the transfer characteristics (vo versus vs) of the circuit shown below. Label all important points, including breakpoints, in the graph. Assume that when conducting in the forward direction, diodes drop 0.75 V. b. [15 points] Verify the results of part (a) using PSpice. Use a DC Sweep for vs ranging from –30 Volts to +30 Volts in steps of 10 mV. c. [15 points] Plot and label the graph of the output voltage versus time, vo(t), when the source vs is as given below. Assume in the following that T = 300 degrees K 2. [20 points] The maximum drift velocity of carriers in silicon is approximately 107 cm/sec. a. [5 points] What is the maximum drift current density that can be supported in an n-type silicon sample with a doping level of 3.5×1017 cm-3 ? 2T T 25V - V 25 s t( ) (Volts) v t b. [10 points] What is the conductivity of the silicon sample? What is its resistivity? Assume that the mobility of electrons is 950 cm2/V.sec. c. [5 points] What is the corresponding voltage drop across the sample if it has a length of 15 cm? 3. [15 points] The free electron concentration in a silicon sample is described by: free electrons per cm3 with Ln equal to 2.5 m. a. [10 points] Find the diffusion current density for electrons as a function of distance if Dn = 13 cm2/sec. b. [5 points] What is the diffusion current at x = 0.75Ln if the cross sectional area is 5000 m2 ? 4. [15 points] A PN junction diode is doped with NA = 2×1017 cm-3 on the p side and ND = 7×1015 cm-3 on the n side. a. [5 points] What are the hole densities in the p-type and in the n-type regions? b. [5 points] What are the free electron densities in the p-type and in the n-type regions? c. [5 points] What is the built-in potential barrier?