Modern Laboratory Methods I: Building and Analyzing Op-Amps Circuits, Lab Reports of Physics

Download Modern Laboratory Methods I: Building and Analyzing Op-Amps Circuits and more Lab Reports Physics in PDF only on Docsity! PHYS 3322 Modern Laboratory Methods I Op Amps II Purpose This experiment will introduce you to the operational amplifier, or op amp, an important building block used in many electronic circuits. Using the op amp, you will construct two useful circuits, a non-inverting amplifier and a sine-wave oscillator. Equipment • Oscilloscope • ± 12 V power supply • Function generator • LT1013 dual op-amp IC • Resistors: 47 Ω, 1 kΩ, 2.7 kΩ (2), 10 kΩ • 1.0 kΩ potentiometer • Capacitors: 100 nF (2) • small incandescent lamp. Procedure You will use the LT1013 integrated circuit in this experiment. The LT1013 contains two complete op amps in one package, as shown in Figure 1. Pin 1 of the integrated circuit is marked with a dot on the package. Pins 4 and 8, labeled with +V and -V in the figure, are the power supply connections. In the following circuits, pin 4 should be connected to the terminal of the power supply, pin 8 should be connected to the −12V +12V terminal of the power supply, and the points marked with the ground symbol should be connected to the terminal of the power supply. 0V Non-inverting amplifier: Using the LT1013 integrated circuit and two 1.0 kΩ resistors, construct the non-inverting amplifier circuit shown in Figure 2. Figure 1. LT1013 integrated circuit. Figure 2. Non-inverting amplifier. Connect a function generator to the input of the amplifier. Using an oscilloscope, adjust the function generator so that its output is a 1 kHz sine wave with the amplitude set at approximately 1 V peak-to-peak. With the oscilloscope, measure the output of the amplifier. You should find that the output amplitude is twice the input amplitude. Verify that this relationship holds true as you vary the input voltage and frequency. Revised: 18 August 2004 1/3 Op Amps II The two resistors control the overall gain of the non-inverting amplifier, a result that can easily be derived from Equation 1 in the previous section. In addition to that equation, we need one other equation, which relates the voltages across the two resistors. To a very good approximation, the current flow into the input terminals of an op amp is zero. Thus, the current through R is equal to the current through , and so we have a simple voltage divider: 1 R2 ( )v R v v Ro− = −/ 1 − / 2 . (2) Rearranging the terms give us v v R R Ro− = +      1 1 2 . (3) Combining this with Equation 1 gives v A R R R Avo 1 1 1 2 + +               = + . (4) Finally, noting that , and using the fact that A>>1 to simplify, we obtain v vi+ = v v R R Ro i = +     1 2 1 . (5) Wien bridge oscillator: The Wien bridge oscillator is a convenient means of generating high- quality (i.e., low distortion) sine waves at audio frequencies. Without disturbing the non- inverting amplifier, construct the Wien bridge oscillator shown in Figure 3. Note that R4 is a potentiometer, not a resistor. The combination of 3 and 4 provide negative feedback, as in the amplifier circuit. The two RC networks provide positive feedback at a frequency determined by the RC time constants. When the positive and negative feedback are precisely in balance, the circuit will oscillate. After assembling and checking the circuit, connect the oscilloscope to the output of the oscillator (pin 1 of the op amp) and apply power. R R Figure 3. Wien bridge oscillator. On the first try, the signal will probably be either a square wave or zero. Adjust the negative feedback loop by varying the setting of the potentiometer 4 until you obtain a sine wave output. At this time, the output will be unstable and the adjustment will be very sensitive. R Revised: 18 August 2004 2/3