EE 2303 Project

Project Assignment

EE 2303/602 - Electronics I

Summer 2001 - due July 30, 2001

All projects should be written on 8.5" x 11" paper with a cover sheet attached. The project report should be stapled only in the upper left-hand corner and no other cover or binder or folder should be used. The cover sheet should include (1) your name, (2) the project title, (3) the course name and number, and (4) your e-mail address. The report should include clearly marked sections on (a) purpose of the project and the theoretical background, (b) a narrative explaining how you did the project, (c) answers to all questions asked in the project assignment, and (d) a list of references used in the order cited in the report (the reference number should appear in the report each time the reference is used). All figures and tables should be clearly marked with a figure or table number and caption. The caption and labels on the figures should make the information in the figure comprehensible without reading further in the text of the report. Auxiliary information (such as SPICE data outputs, etc.) should be included in appropriate Appendices at the end of the report. Be sure to describe exactly how all results were obtained, giving enough information for anyone who understands EE 2303 to repeat your work. All work submitted must be original. If derived from another source, a full bibliographical citation must be given. (See all of Notes 5 and 6 in the syllabus.) Download a sample project solution - solution.doc

Diode Load Line Quiescent Point:

Comparison of the Iterative Solution to the PSpice Solution

Purpose: The purpose of this project will be to compare the solution for the load line quiescent point obtained by an iterative method with that obtained using PSpice.

The circuit used is shown in Figure 1. The diode current, i_D, is a function of the diode voltage, v_D, and is the simultaneous of two equations, the load-line equation and the Shockley equation for the diode.

Figure 1. The schematic diagram pertinent to this project. The diode current, i_D, is the current flowing in the diode in the direction of the arrow. The diode voltage, v_D, is the voltage drop across the diode.

The load line equation gives the relationship between the current, i_L, drawn from the ideal source, V, and the voltage drop, v_L (= V - i_LR). Thus,

Equation 1 i_L = (V - v_L)/R

The Shockley equation gives the diode current, i_D, as a function of the diode voltage, v_D, with

Equation 2 i_D = IS [exp(v_D/(NV_t))-1],

where IS is the saturation current density, N is the ideality factor and V_t (= kT/q) is the thermal voltage (k is the Boltzman constant, T is the absolute temperature and q is the electron charge).

Iteration: To obtain the solution by iteration, each step consists of calculating the current by using Equation 1 (with the exception of step 1, where i_L1 = V/(2R) ), and then calculating the voltage by noting that by the Kirchoff current law, i_L = i_D, and subsequently using Equation 2 in inverted format (v_D = NV_t ln[(i_D/IS) + 1]). Thus,

Iteration 1: i_L1 = V/(2R) = i_D1, then v_D1 = NV_t ln[(i_D1/IS) + 1]

Iteration 2: i_L2 = (V- v_D1)/R = i_D2, then v_D2 = NV_t ln[(i_D2/IS) + 1]

Iteration 3: i_L3 = (V- v_D2)/R = i_D3, then v_D3 = NV_t ln[(i_D3/IS) + 1] ]

…]

Iteration n: i_Ln = (V- v_D(n-1))/R = i_Dn, then v_Dn = NV_t ln[(i_Dn/IS) + 1]

The iteration process is usually continued until the differential error ratio, D,

Equation 3 D = |i_Dn - i_D(n-1)|/i_Dn

is less than some predetermined fractional difference (i.e., 1%, etc.).

Obtaining the PSpice solution: First, the solutions cannot be compared unless the same value for V_t is used. The value to be used throughout the entire project is V_t = 25.852 mV.

Question 1. Verify from the Shockley equation that when an independent current source drives a current of i_D = IS(exp(1) - 1), the voltage measured across the diode should be NV_t.

Question 2. Using a circuit as defined in Question 1, determine the values that should be used for the PSpice Analysis/Setup/Option parameters, GMIN, NUMDGT, and TNOM in order for the value of V_t = 25.852 mV to at least 5 significant figures for the diode defined in Question 3.

Question 3. Given that IS = 2E-12, N = 1.08, V = 3 Volts, and R = 0.1, 0.3, 1, 3, 10, 30, 100, 300, and 1,000 Ohms, use PSpice to determine the quiescent point values for i_DQ and v_DQ corresponding to each R value given. Report your results in the form of a table with column headings R, i_DQ and v_DQ and a row for each of the values of R given above. Be sure the number of significant figures reported for i_DQ is commensurate with 5 significant figures for v_DQ as is appropriate from Question 2 above.

Obtaining the Iterated Solutions:

Question 4. Using the iterative procedure defined above to determine the quiescent point values for the same circuit parameters defined in Question 3. Perform the iterative procedures in each case until the value of D is < 1%.. Report your 1% results in the form of a table with column headings R, i_DQ,1% and v_DQ,1% and a row for each of the values of R given above. Be sure the number of significant figures reported for i_DQ is commensurate with 5 significant figures for v_DQ as is appropriate from Question 2.

Question 5. Compare the PSpice and iterative results by calculating the relative difference, r, between the PSpice-calculated current, i_DQ, and the iterative solution, i_DQ,1% (r = |i_DQ - i_DQ,1%|/i_DQ). Tabulate the r values for each value of R given in 3. Comment on the magnitude of r, and any trends observed.