EECE 310 Exam 1, Fall 2004

EECE 310 – Quiz 1 – Fall 2004/2005 – Page 1 of 10 American University of Beirut P1 /16 Department of Electrical and Computer Engineering P2 /12 EECE 310 – Electronics I P3 /12 Fall 2004 – 2005 P4 /12 Quiz 1 – November 5, 2004 P5 /6 Closed Book – 90 minutes P6 /12 P7 /10 P8 /10 P9 /10 Grade /100 NAME:___________________________ ID Number: ______________________ I have neither given nor received aid on this exam SIGNATURE ASSUME VT = 25 mV, UNLESS OTHERWISE SPECIFIED Problem 1 [16 points] An amplifier is characterized by the following relationships between its output voltage and its input voltage: vO = 1 V for vI < 2 V vO (in V) = 3 vI – 5 for 2 V ≤ vI ≤ 3 V vO = 4 V for vI > 3 V a) Plot the amplifier transfer characteristics (vO versus vI) for 0 V ≤ vI ≤ 5 V. [3 points] vI (V) vO (V) 5 1 1 2 3 4 2 3 4 5 EECE 310 – Quiz 1 – Fall 2004/2005 – Page 2 of 10 b) In the amplification region, what is the gain of the amplifier (in V/V)? What is the gain of the amplifier in dB? [3 points] c) What is the maximum peak-to-peak undistorted variation in the output voltage? What is the corresponding peak-to-peak variation in the input voltage? [3 points] d) Where should the bias point (VI, VO) of this amplifier be in order to get the maximum undistorted output? [3 points] e) For the input waveform shown below, plot and label, on the same graph, the output waveform. [4 points] time voltage (V) 1 2 3 4 5 EECE 310 – Quiz 1 – Fall 2004/2005 – Page 3 of 10 Problem 2 [12 points] Measurements on a Si diode were taken at vD = 0.35 V, 0.45 V, 0.55 V, and 0.65 V. The natural logarithm of the diode current in Amps, ln(iD), is plotted on the y-axis versus vD in Volts, on the x-axis. The resulting straight-line has a slope of 32, and a y- axis intercept of –30. a) For this diode, find the values of n and IS. [8 points] b) What is the diode current when vD = 0.7 V? [4 points] EECE 310 – Quiz 1 – Fall 2004/2005 – Page 4 of 10 Problem 3 [12 points] The diodes in the circuit shown drop 0.7 V when conducting. Calculate the current in D2 and the voltage across R3. Verify all your assumptions. 15 V 15 V R1 = 5K R2 = 10K R3 = 10K D1 D2 R4 = 5K EECE 310 – Quiz 1 – Fall 2004/2005 – Page 5 of 10 Problem 4 [12 points] A certain device X is described by the following I-V characteristic: X X X v v i = 4 + iX is in mA and vX is in Volts This device is connected in series with a 2 KΩ resistor and a 3 V battery as shown below. 3 V 2 K X iX vX + - a) Using numerical iterations, and starting with vX = 0.8 V, find the values of vX and iX for the device in this circuit. Show all steps in the calculation, and stop the iterations when consecutive values of vX do not differ by more than 2 mV in absolute value. [6 points] EECE 310 – Quiz 1 – Fall 2004/2005 – Page 6 of 10 b) Plot the I-V characteristic for the device on the graph below at values of vX = 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and 1.1 V. Then, use the load line method to graphically determine iX and vX. [6 points] v (V) i (mA) 2 1 1 2 3 Problem 5 [6 points] A Si diode is biased at a DC current of 5 mA. What is the peak-to-peak signal current that can appear in the diode without exceeding the small-signal approximation limit? EECE 310 – Quiz 1 – Fall 2004/2005 – Page 7 of 10 Problem 6 [12 points] A full-wave rectifier with a center-tap transformer uses two diodes that are assumed ideal. The average value of the output voltage is 10 V, across a 100 Ω load resistor. a) Find the maximum value of the sinusoidal voltage at the secondary of the transformer (from the center tap to one of the transformer terminals on the secondary.) [4 points] b) Find the average diode current. [4 points] c) Find the diode PIV. [4 points] Problem 7 [10 points] R + 2V vo + - vs 3V 2R D1 D2 For the vS waveform shown below, plot and label, on the same graph, the output waveform that is produced by the circuit shown above. EECE 310 – Quiz 1 – Fall 2004/2005 – Page 8 of 10 time voltage (V) -5 0 5 10 -10 Problem 8 [10 points] The Zener diode shown in the circuit below is rated at VZ = 12 V for a test current of 25 mA. The value of the incremental Zener resistance rZ is 10 Ω. The Zener knee current IZK is 5 mA. Find the Zener current and the Zener voltage in the circuit shown. Verify all assumptions. EECE 310 – Quiz 1 – Fall 2004/2005 – Page 9 of 10 +20V 150 Ω 820 Ω -10V EECE 310 – Quiz 1 – Fall 2004/2005 – Page 10 of 10 Problem 9 [10 points] The density of donor atoms in a semiconductor is 5×1016 cm-3. The mobility of electrons in the semiconductor is 1300 cm2/V.sec and that of holes is 500 cm2/V.sec. The intrinsic density is ni = 1.5 x 1010 cm-3. The magnitude of electron charge is 1.6×10-19 C. a) Is the semiconductor N-type or P-type? Why? [2 points] b) Find the hole concentration. Does the hole concentration increase, decrease, or remain unchanged when temperature increases? [2 points] c) Find the concentration of free electrons. Does the free electron concentration increase, decrease, or remain unchanged when temperature increases? [2 points] d) Calculate the conductivity of the semiconductor. [2 points] e) Find the drift current density due to holes if an electric field of 104 V/cm is applied. [2 points] Not included in the material of Quiz 1 for Fall 2006 - 2007