CTU: EE 415 – Advanced Electronics: Lab 3: Curve Tracer 1 Colorado Technical University EE 415 – Advanced Electronics Lab 3: Curve Tracer September 2010 Loren K. Schwappach ABSTRACT: This lab report was completed as a course requirement to obtain full course credit in EE415,Advanced Electronics at Colorado Technical University. This report examines the components of a curve tracer by buildingupon knowledge gained from previous labs. If you have any questions or concerns in regards to this laboratory assignment, this laboratory report, the processused in designing the indicated circuitry, or the final conclusions and recommendations derived, please send an email toLSchwappach@yahoo.com. I. INTRODUCTION IV. PROCEDURES / RESULTS A curve tracer is used to model the current versus This section outlines the procedures required tovoltage characteristics of transistors and other devices. In reproduce this lab and obtain similar results.this lab assignment a general curve tracer design is attemptedusing previous Op-Amp circuit designs. The final design(curve tracer) is finally tested and the results were verified by A. PART 1 – 1 KHZ OSCILLATORthe course instructor. The 1k Hertz oscillator is the first major component II. OBJECTIVES of the curve tracer. This oscillator is used to drive the rest of the circuit, specifically a integrator and step generator. As previously mentioned, this lab assignment builtupon designs created from previous labs, specifically the i. CALCULATIONS:integrator and oscillator as sources for a transistor curvetracer. The final curve tracer design included A 1k Hertz Schmitt Trigger Circuit:oscillator, a step generator, and a reset circuit all designedand verified using Multisim prior to physical circuitconstruction. III. DESIGN APPROACHES/TRADE-OFFS Oscillator Circuit: Hand calculations for the oscillator and integratorwere completed on previous labs. However as noted inprevious labs a few modifications to each design becamenecessary to ensure optimal RC combinations. Finally, thestep generator and reset circuit required several hours ofexperimentation in Multisim to produce and figure out goodresistor values to use for the reset circuitry. ii. EQUIPMENT: +/- 15 Volts Direct Current (VDC) Power Source Signal Generator Breadboard Three (3) 412k Ohm Resistors One (1) 1n Farad Capacitor
CTU: EE 415 – Advanced Electronics: Lab 3: Curve Tracer 2 741 Op-Amp iv. RESULTS: Multisim Version 11, by National Instruments As shown by Figure 2 the oscillator correctly Oscilloscope produced a 15 Vp signal oscillating at 1k Hertz. iii. CIRCUIT DIAGRAM: Figure 2: Multisim Transient Analysis Results of 1k Hertz oscillator. Figure 3: Oscilloscope results of 1k Hertz oscillator. B. PART 2 – 1 KHZ INTEGRATOR The integrator circuit takes in the 15Vp square wave produced by the oscillator and outputs a 15Vp triangle wave for use by the curve tracer. i. CALCULATIONS:Figure 1: Multisim 1 KHz Oscillator, designed the same asthe oscillator in lab #2 but using different RC values. (8) (9) (10) ii. EQUIPMENT: +/- 15 Volts Direct Current (VDC) Power Source Signal Generator Breadboard One (1) 226k Ohm Resistor One (1) 1k Ohm Resistor
CTU: EE 415 – Advanced Electronics: Lab 3: Curve Tracer 3 One (1) 1n Farad Capacitor 741 Op-Amp Multisim Version 11, by National Instruments Oscilloscope iii. CIRCUIT DIAGRAM: Figure 5: Multisim transient analysis results of integrator output. Figure 6: Oscilloscope results of integrator output (blue) and oscillator output yellow. C. PART 3 – STEP GENERATOR AND RESET CIRCUIT The step generator took in the 1k Hertz oscillator square wave output and generated a rising step pattern. The number of steps produced was dependent upon the input voltage provided to the reset circuit (comparator). The two diodes (D1 and D2) allowed rectification of the oscillatorFigure 4: Multisim 1 KHz Integrator, designed the same as output and ensured that the step generators outputthe Integrator in lab #1 but using different RC values. increased each cycle of the oscillator until finally reset by the reset circuit. iv. RESULTS: The reset circuit compared the step generators output with an externally provided (via voltage divider) bias As shown by Figure 5 the integrator correctly to allow the resetting of transistor Q2. When transistor Q2 isproduced a 15 Vp signal oscillating at 1k Hertz. The oscillator conducting it is in the reset condition, and provides a path forand integrator outputs are shown side by side on the current around capacitor C4 (not yet shown). When C4oscilloscope display Figure 6. discharges the output and input of the step generator equalize resetting the step generator. i. CALCULATIONS: No calculations were required, because the step generator and reset circuitry was provided by the instructor. However, modifications to the step generator and reset circuits were required to component availability (capacitors). Finally the instructors design was improved by using variable resistors (potentiometers) in Multisim,
CTU: EE 415 – Advanced Electronics: Lab 3: Curve Tracer 4changing the Reset comparators input voltage andexperimenting with different resistance values. Theseexperiments led to the final circuit diagram displayed asFigures 2 and Figure 8. ii. EQUIPMENT: +/- 15 Volts Direct Current (VDC) Power Source Signal Generator Breadboard One (1) 100k Ohm Resistor One (1) 87.5k Ohm Resistor One (1) 80k Ohm Resistor One (1) 30k Ohm Resistor One (1) 5k Ohm Resistor One (1) 1k Ohm Resistor One (1) 1n Farad Capacitor Two (2) Diodes (PN: 1N4001) Two (2) 741 Op-Amps Multisim Version 11, by National Instruments Oscilloscope Figure 8: Multisim Reset Circuit. iii. CIRCUIT DIAGRAM: iv. RESULTS:. As shown by Figure 3 the step circuit correctly produced approximately 5 to 7 steps (nominally 6) before the reset circuit reset the step generator. Each step occurs at approximately 1ms (1k Hertz). The reset circuit caused a reset when the input reset voltage reached an externally generated reference voltage. The largest influence on the number of steps created is due to the difference between capacitors C4 (not yet shown) and C3. Increasing C4 will significantly increase the number of steps produced.Figure 7: Multisim Step Generator. Figure 9: Multisim transient analysis results of step generator (green) and reset circuit (red). .
CTU: EE 415 – Advanced Electronics: Lab 3: Curve Tracer 5Figure 10: Oscilloscope results of step generator (yellow)and reset circuit (blue). i. CALCULATIONS: No calculations are required for this step. All thatwas required was to put all of the components together. ii. EQUIPMENT:All of the previous equipment to include the followingadditional equipment:The (may be modified) resistor values may be amended tocreate any shifted / weighted value of Ic vs. Vce curves. +/- 15 Volts Direct Current (VDC) Power Source Signal Generator Large Breadboard Two (2) 100k Ohm Resistors (may be modified) One (1) 500k Ohm Resistor (may be modified) One (1) 15n Farad Capacitor Multisim Version 11, by National Instruments Oscilloscope
CTU: EE 415 – Advanced Electronics: Lab 3: Curve Tracer 6 iii. CIRCUIT DIAGRAM:.Figure 11: Final Multisim Circuit Diagram showing finalized curve tracer design. iv. RESULTS: Figure 13: Oscilloscope results of curve tracer circuit.Figure 12: Multisim transient analysis results of oscillator(purple), Integrator (blue), step generator (green), and reset(red).
CTU: EE 415 – Advanced Electronics: Lab 3: Curve Tracer 7 V. CONCLUSIONS All component circuitry correctly produced the desired responses. The oscillator correctly produced a 1k Hertz output, the integrator correctly integrated that output into a 1k Hertz triangle wave and the step generator and reset circuitry correctly produced five steps. Component availability and selection were extremely limiting factors in this lab and forced the redesigning of the step generator and reset circuitry in order to account for a lack of resistors and small (1pF and 10pF capacitors) as provided by the instructors reference document. Further explanation of the Ic vs. Vce curves as a function of resistors R8, R12, and R13 would have enhancedFigure 14: Curve tracer results. Ic left, Vce bottom. the final oscilloscope curves (not shown). REFERENCES  Neamen, D. A., “Microelectronics Circuit Analysis and rd Design 3 Edition” John Wiley & Sons, University of New Mexico, 2007.