# Spice_Hwk - ECE 255 ELECTRONIC ANALYSIS AND DESIGN Fall...

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0 V 0Vdc D1 D1N4148 I ECE 255 ELECTRONIC ANALYSIS AND DESIGN Fall 2011 SPICE Homework Due Friday, September 9 5:00 p.m. Room MSEE 180 Drop Box Based on ECE 208 Lab 3 1. Using any SPICE based simulation system, plot the V-I characteristics of a 1N4148 diode. Most PC based programs already contain the 1N4148 diode model; however, if you are using http://www.nanohub.org/ you will need to input model parameters. Below are the model parameters used by the Cadence PSpice program. .model D1N4148 D(Is=2.682n N=1.836 Rs=.5664 Ikf=44.17m Xti=3 Eg=1.11 Cjo=4p + M=.3333 Vj=.5 Fc=.5 Isr=1.565n Nr=2 Bv=100 Ibv=100u Tt=11.54n) The V-I characteristics are obtained by performing a D.C. Voltage Sweep using the following circuit. Sweep the D.C. voltage from –0.2 V to 1.0 V to obtain a plot similar to the graph below. 2. Using the cursor, “Mark” a point at about –0.1 V to estimate the value of I S (as shown above) and record the result on the cover sheet. 3. Plot the dynamic resistance of the diode logarithmically to obtain a plot similar to the plot below. Diode Current Dynamic Resistance (-100m, ???)

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0 VSIN FREQ = 5kHz VAMPL = 10mV VOFF = 0V C1 1uF D1 D1N4148 R1 10k Vcc ?? Vdc 0 Vcc R2 ?? k Vcc + Vout C-coupling 10n R-scope 1Meg Oscilloscope V The dynamic resistance r d is the reciprocal of the slope of the diode I-V characteristic evaluated at the operating point, Q. D T T d D D S D V V V r I I I I Q d d η η = = + (for forward bias) where η is the ideality factor and V T is the thermal voltage. Since the PSpice simulation assumes a temperature of 27°C, T T V 25.87mV k q = = . 4. Modify your plot to provide an estimate of the ideality factor. That is, plot D d T I r V η = . 5. Using the cursor “Mark” a point at about 0.3 V to estimate the value of η (as shown above) and record the result on the cover sheet. NOTE: Our approximation requires that the diode be forward biased but we note that the diode behavior begins to deviate from that of an ideal diode at both very low and high currents. Now that we know all about our diode’s characteristics, let’s build something! How about a variable attenuator?
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## This note was uploaded on 02/12/2012 for the course ECE 255 taught by Professor Staff during the Fall '08 term at Purdue University-West Lafayette.

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Spice_Hwk - ECE 255 ELECTRONIC ANALYSIS AND DESIGN Fall...

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