EE122 Homework Set 3 Question 1: Using figures 1 and 2 verify that Io and η are within 5% of 10‐12A and 1.0 respectively at room temperature (@300K, kT/q=.0259V) Figure 1: LTspice schematic for a simple diode with Io=10‐12A, andη(ideality factor)=1.0. Figure 2: Plot of ln(Id) vs. the applied diode voltage, used to extract Io and η(ideality factor). Use easy to read points. M=(y2‐y1)/(x2‐x1)=(‐6‐‐18)/(.56‐.245)=38.095 B=y2‐mx2=‐6‐38.095x.56=‐27.33 Is=exp(b)=1.32x10‐12A N=1/M/VT=1/38.095/.0259=1.01 Question 2: Using figure 3 extract Io and η to within 5% at room temperature (@300K, kT/q=.0259V). Figure 3: Plot of ln(Id) vs. applied voltage for a diode with an unknown Io and η. M=(y2‐y1)/(x2‐x1)=(‐8‐‐12)/(.385‐.210)=22.857 B=y2‐mx2=‐6‐38.095x.56=‐16.799 Is=exp(b)=5.05x10‐8A N=1/M/VT=1/22.857/.0259=1.68 Question 3: A student used figure 4 extract Io and η to within 5% at room temperature (@300K, kT/q=.0259V). The extracted Io and η were 1.5x10‐13A and 0.38. Explain why the extracted values do not “make sense”. What do you think happened? Be specific. N in general should be between 1 and 2. Since n is much less than 1, the slope extracted must have been to high. The student extracted the values in the wrong spot. Figure 4: Plot of ln(Id) vs. applied voltage for a diode with an unknown Io and η. Question 4: A student used figure 5 extract Io and η to within 5% at room temperature (@300K, kT/q=.0259V). The extracted Io and η were .9999A and 643500. Explain why the extracted values do not “make sense”. What do you think happened? Be specific. Figure 5: Plot of Id vs. applied voltage for a diode with an unknown Io and η. Given that n is much much greater than 2 the slope must have been too small. We can see that the student used the wrong area when Rs is dominating the performance. Question 6: Find the input voltage range for which the following diodes can be used for the ex function. • 1N4148(Motorola) • 1N914 (Motorola) • NSSWS108T (Nichia) Figure 6: The two Motorola diodes have the same range of .1V to .6Volts. The Nichia diode is an LED and requires more voltage to turn on: Figure 7: Voltage range is 1.2 to2.6 Volts.
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