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CTU: EE 415 – Advanced Electronics: Lab 2: Oscillators 1 Colorado Technical University EE 415 – Advanced Electronics Lab 2: Oscillators August 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 introduces two resonating oscillators built using threeresistors, a capacitor, and an Op-Amp. 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 i. CALCULATIONS: Schmitt Trigger Circuit: Operational amplifiers (Op-Amps) in feedbackcircuitry can be utilized for advanced signal conditioning aswell as linear amplification. Their performance is generallylocked upon their frequency linearity and feedback design.An oscillator utilizes positive feedback and a triggering toproduce a square wave output. Oscillator Circuit: II. OBJECTIVES This lab uses an operational amplifier (Op-Amp) todesign and build two oscillators. The first Op-Amp resonatesat 200 Hertz and the second resonates at 25k Hertz. III. DESIGN APPROACHES/TRADE-OFFS ii. EQUIPMENT: In order to simplify the design of each oscillator To effectively reproduce the circuits built in this labhand calculations were simplified by ensuring the values of you will require the following components/parts/software.each resistor were identical (R1=R2=R3=Rx). +/- 5 Volts Direct Current (VDC) Power Source IV. PROCEDURES / RESULTS Signal Generator Breadboard Three (3) 2.365M Ohm Resistors This section outlines the procedures required toreproduce this lab and obtain similar results. 741 Op-Amp Multisim Version 11, by National Instruments A. PART 1 – 200 HZ OSCILLATOR Oscilloscope To design the 200 Hz oscillator using a 1n Faradcapacitor, a resistance value of 2.275M ohms was calculatedusing equation (6). After verifying the output frequency withMultisim this resistance value was increased to 2.365M ohmsproducing a better frequency result.
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CTU: EE 415 – Advanced Electronics: Lab 2: Oscillators 2 iii. CIRCUIT DIAGRAM: From Figure 2 it is observed the 200 Hertz oscillator correctly produced the 200 Hertz square wave. This was further verified by the oscilloscope. Figure 3: Oscilloscope results of 200 Hertz oscillator circuit. . B. PART 2 – 25 KHZ OSCILLATOR After recalculating the resistor values using equation (6) a value of 18.2k Hertz was chosen. However, after simulating the circuit in Multisim it was discovered that a resistor value of 5.5k ohms produced a frequency very close to 25k Hertz. However, due to the slow switching speed of the 741 Op-Amp, due to its parasitic resistance and capacitance, the output waveform appeared more like a triangle wave than a square wave. Thus the 25k Hz Op-Amp design performed very poorly as an oscillator circuit. i. CALCULATIONS: The equations for the 25k Hertz oscillator were the same asFigure 1: Multisim design of 200 Hertz oscillator. the 200 Hertz oscillator. Schmitt Trigger Circuit: iv. RESULTS: Oscillator Circuit:Figure 2: Multisim transient analysis results of 200 Hertzoscillator.
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CTU: EE 415 – Advanced Electronics: Lab 2: Oscillators 3 ii. EQUIPMENT: iv. RESULTS: +/- 5 Volts Direct Current (VDC) Power Source Signal Generator Breadboard Three (3) 5.5k Ohm Resistors 741 Op-Amp Multisim Version 11, by National Instruments Oscilloscope iii. CIRCUIT DIAGRAM: Figure 5: Multisim transient analysis results of 25k Hertz oscillator. From Figure 5 it is observed the 25k Hertz oscillator produced a 25k Hertz signal, however as a square wave the signal was very distorted demonstrating the slow frequency response of the oscillator due to parasitic resistance and capacitance. This was further verified by the oscilloscope. Figure 6: Oscilloscope results of 25k Hertz oscillator circuit. C. PART 3 –200 HZ WORST CASE (-20%R AND +20%R) The next stage in the lab was to verify the worst case behavior of oscillator with resistors lower (-20%) than the calculated value, and with resistors higher (+20%) than theFigure 4: Multisim design of 25k Hertz oscillator. calculated value. The 200 Hertz oscillator resistance value of 2.28M ohms was used as the base resistance. Using this values for the worst high and low case were obtained. i. CALCULATIONS:
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CTU: EE 415 – Advanced Electronics: Lab 2: Oscillators 4 ii. EQUIPMENT: +/- 5 Volts Direct Current (VDC) Power Source Signal Generator Breadboard Three (3) 1.82M Ohm Resistors Three (3) 2.73M Ohm Resistors 741 Op-Amp Multisim Version 11, by National Instruments Oscilloscope iii. CIRCUIT DIAGRAM: Figure 3: Multisim design of 200 Hertz oscillator, Worst case scenario, high resistance, +20%. iv. RESULTS: The worst case low scenario produced a 164 Hertz oscillating signal, while the worst case high scenario produced a 175 Hertz signal. The calculated resistance produced a 169 Hertz signal.Figure 2: Multisim design of 200 Hertz oscillator, Worst casescenario, low resistance, -20%.
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CTU: EE 415 – Advanced Electronics: Lab 2: Oscillators 5 Figure 7: Oscilloscope results of 200 Hertz oscillator circuit displaying worst case high results. V. CONCLUSIONSFigure 4: Multisim transient analysis of 200Hz worst case The Op-Amp oscillator circuit utilized a hysteresislow circuit. loop to create oscillation from the positive feedback of a Schmitt trigger. This coupled with slow negative feedback created oscillation. Conditions for oscillation include a charged storage device (capacitor/inductor) and a resistor to control the oscillation frequency. REFERENCES [1] Neamen, D. A., “Microelectronics Circuit Analysis and rd Design 3 Edition” John Wiley & Sons, University of New Mexico, 2007.Figure 5: Multisim transient analysis of 200Hz worst casehigh circuit.Figure 6: Oscilloscope results of 200 Hertz oscillator circuitdisplaying worst case low results..
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