4 ee414 - adv electroncs - lab 3 - loren schwappach

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 building upon knowledge gained from previous labs.

If you have any questions or concerns in regards to this laboratory assignment, this laboratory report, the process used in designing the indicated circuitry, or the final conclusions and recommendations derived, please send an email to [email protected].

I. INTRODUCTION

A curve tracer is used to model the current versus voltage characteristics of transistors and other devices. In this lab assignment a general curve tracer design is attempted using previous Op-Amp circuit designs. The final design (curve tracer) is finally tested and the results were verified by the course instructor.

II. OBJECTIVES

As previously mentioned, this lab assignment built upon designs created from previous labs, specifically the integrator and oscillator as sources for a transistor curve tracer. The final curve tracer design included A 1k Hertz oscillator, a step generator, and a reset circuit all designed and verified using Multisim prior to physical circuit construction.

III. DESIGN APPROACHES/TRADE-OFFS

Hand calculations for the oscillator and integrator were completed on previous labs. However as noted in previous labs a few modifications to each design became necessary to ensure optimal RC combinations. Finally, the step generator and reset circuit required several hours of experimentation in Multisim to produce and figure out good resistor values to use for the reset circuitry.

IV. PROCEDURES / RESULTS

This section outlines the procedures required to reproduce this lab and obtain similar results.

A. PART 1 – 1 KHZ OSCILLATOR

The 1k Hertz oscillator is the first major component of the curve tracer. This oscillator is used to drive the rest of the circuit, specifically a integrator and step generator.

i. CALCULATIONS:

Schmitt Trigger Circuit:

Oscillator Circuit:

ii. EQUIPMENT:

+/- 15 Volts Direct Current (VDC) Power Source

Signal Generator

Breadboard

Three (3) 412k Ohm Resistors

One (1) 1n Farad Capacitor

mailto:[email protected]?subject=CTU%20-%20EE414%20-%20Adv.%20Electronics%20-%20Lab%201


741 Op-Amp

Multisim Version 11, by National Instruments

Oscilloscope

iii. CIRCUIT DIAGRAM:

Figure 1: Multisim 1 KHz Oscillator, designed the same as the oscillator in lab #2 but using different RC values.

iv. RESULTS:

As shown by Figure 2 the oscillator correctly produced a 15 Vp signal oscillating at 1k Hertz.

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:

(8)

(9)

(10)

ii. EQUIPMENT:


Signal Generator

Breadboard

One (1) 226k Ohm Resistor




741 Op-Amp


Oscilloscope


Figure 4: Multisim 1 KHz Integrator, designed the same as the Integrator in lab #1 but using different RC values.

iv. RESULTS:

As shown by Figure 5 the integrator correctly produced a 15 Vp signal oscillating at 1k Hertz. The oscillator and integrator outputs are shown side by side on the oscilloscope display Figure 6.

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 oscillator output and ensured that the step generators output increased each cycle of the oscillator until finally reset by the reset circuit. The reset circuit compared the step generators output with an externally provided (via voltage divider) bias to allow the resetting of transistor Q2. When transistor Q2 is conducting it is in the reset condition, and provides a path for current around capacitor C4 (not yet shown). When C4 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,


changing the Reset comparators input voltage and experimenting with different resistance values. These experiments led to the final circuit diagram displayed as Figures 2 and Figure 8.

ii. EQUIPMENT:


Signal Generator

Breadboard


One (1) 87.5k Ohm Resistor






Two (2) Diodes (PN: 1N4001)

Two (2) 741 Op-Amps


Oscilloscope


.

Figure 7: Multisim Step Generator.

Figure 8: Multisim Reset Circuit.

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 9: Multisim transient analysis results of step generator (green) and reset circuit (red). .


Figure 10: Oscilloscope results of step generator (yellow) and reset circuit (blue).

i. CALCULATIONS:

No calculations are required for this step. All that was required was to put all of the components together.

ii. EQUIPMENT:

All of the previous equipment to include the following additional equipment: The (may be modified) resistor values may be amended to create any shifted / weighted value of Ic vs. Vce curves.


Signal Generator

Large Breadboard

Two (2) 100k Ohm Resistors (may be modified)

One (1) 500k Ohm Resistor (may be modified)



Oscilloscope



.

Figure 11: Final Multisim Circuit Diagram showing finalized curve tracer design.

iv. RESULTS:

Figure 12: Multisim transient analysis results of oscillator (purple), Integrator (blue), step generator (green), and reset (red).

Figure 13: Oscilloscope results of curve tracer circuit.


Figure 14: Curve tracer results. Ic left, Vce bottom.

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 enhanced the final oscilloscope curves (not shown).

REFERENCES

[1] Neamen, D. A., “Microelectronics Circuit Analysis and Design 3

rd Edition” John Wiley & Sons, University of New

Mexico, 2007.

4 ee414 - adv electroncs - lab 3 - loren schwappach

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