advertisement

ADANA SCIENCE AND TECHNOLOGY UNIVERSITY ELECTRICAL – ELECTRONICS ENGINEERING DEPARTMENT ELECTRICAL CIRCUITS LABORATORY II EEE 209 EXPERIMENT-6 Operational Amplifiers II OPERATIONAL AMPLIFIERS Objectives The goal of this experiment is to study operational amplifier (op amp) and its applications in alternative current conditions. Some basic op‐amp circuits, including the most common types, i.e., the inverting, non‐inverting, integrator and differentiator will be introduced, simulated and applied on a board. Introduction Please read the introduction part of the previous experiment (Op-amp experiment I), it is also available for this experiment. Equipment Breadboard Cables & Wires and connectors Operational Amplifier Digital Oscilloscope, Multimeter Signal Generator, DC Power Supply, Resistors Preliminary work (Calculation and simulation section) 1) Derive the gain (Vout/Vin) expression in terms of R1 , R2 and C for the following amplifiers. R2 Vin AC R1 C +Vcc + Vout -Vcc Figure 1. View of a derivator 2) Show the relation of output and input voltage of the following circuit (Integration) Figure 2. View of an integrator amplifier 3) Simulate the circuit of Figure 3, Figure 4, and Figure 6 record all the voltage and current values in a table. Experiment Inverting Op-amp R2 R1 Vin AC +Vcc + Vout -Vcc Figure 3. View of an integrator As mentioned in the previous experiment, the op-amp must be connected to an external power supply. Since we want to produce both positive and negative output voltages, we need both positive and negative voltages for the power supply. For a uA741 operational amplifier, the nominal values are +15V for positive supply and -15V for negative supply. Construct the circuit with R1=10K and R2=100K values as shown in Figure 3. Connect the function generator output to Vin of the circuit given in Figure 3. Turn on the function generator and apply a proper sinusoidal signal to Vin. Observe the output from the scope. Note that, the output signal must not be clipped. Change the R2 value for 68K, 39K, and 10K. For each step write down the output voltage and gain. (To change its value disconnect the R2 from the circuit and then do your measurement). For each step save the snapshot of the oscilloscope which includes Vout and Vin. Non-inverting Op-amp Non-inverting (positive gain) circuit configuration is shown in Figure 4. The voltage gain of the noninverting amplifier circuit is obtained as below; Vout R 1 2 Vin R1 R2 R1 +Vcc + Vout -Vcc AC Figure 4. View of an non-inverting amplifier Connect the circuit under test according to the Figure 4. Change the R2 value as done before in the previous experiment and write down the results. At the end of your experiment plot the gain-R2 graph and compare it with the ideal one. Differentiator and Integrator By introducing electrical reactance into the feedback loops of op-amp amplifier circuits, we can cause the output to respond to changes in the input voltage over time. Deriving their names from their respective calculus functions, the integrator produces a voltage output proportional to the product (multiplication) of the input voltage and time; and the differentiator (not to be confused with differential) produces a voltage output proportional to the input voltage's rate of change. In Figure 5 and Figure 6, integrator and differentiator circuits are given respectively. The output voltage of an integrator is given in the following equation. Vo 1 Vin dt Vo (t 0) RinC C1 R2 Vin Rin +Vcc + AC Vout -Vcc Figure 5. View of an integrator On a separate piece of paper, sketch the integral of the following waveforms: a) Sinusoidal waveform b) Triangular waveform c) Square waveform Connect the integrator shown in Figure 5. Please, use the following values for the components and voltages R2=4.7 kΩ, Rin=47kΩ, C=0.1µF, Set the function generator to provide the following input signals: A. Vin=1.5 VPP, 2 KHz, sin wave B. Vin=1.5 VPP, 2KHz, square wave, C. Vin=1.5 VPP, 2 KHz, triangular wave Turn on the output of the power supply to provide the +15 V and -15 V to the Op Amp. Connect the signal generator to the input terminal Vin of your integrator. Measure the voltage and frequency of the output waveforms. Repeat this for each of the inputs and record these values in the Table and save snapshots of Vout with the corresponding input for each of the three cases. Waveform, Vin Vout Frequency Differentiator Suppose that, a sine function sin(t ) is applied to the input of a differentiator. In this case, the output will be the derivative of this function, which is .cos(t ) . So, when the input frequency is increased, the gain of this circuit also increases. But please note that, the op-amp will not operate properly after a certain frequency value. R2 Vin Rin +Vcc C + Vout AC -Vcc Figure 6. View of a differentiator Vo R2C dV1 dt In some applications, it may be possible to add a series input resistor, as shown in Figure 6. This limits the high frequency gain of the circuit to the ratio R/Rin. The low frequency cutoff is set by R2 and C. The high frequency cutoff is determined by Rin and C, according to the expression: fco 1/ 2 RinC . Experiment: Construct the differentiator amplifier with the circuit elements as given in Figure 6. SET1= Rin=47Ω, R2=1KΩ, C=0.1 µF. SET2= Rin=470Ω, R2=10KΩ, C=22 nF. What are the high frequency and low frequency cutoff of differentiator amplifier with Set1 and Set2 circuit elements? Please verify theoretically! Apply an asymmetric triangle wave with proper amplitude and frequency to the input of the circuit. Use the function generator to set Vin to a 1 V peak-to-peak triangle wave. Using both channels of the oscilloscope, observe and record the relationship between input and output for input frequencies of 500 Hz and 1kHz. Compare the results with what you obtain by theoretically. Repeat the experiment using a sine-wave input signal. Please be sure to note the phase relationship between input and output. Record the input and output signals of the circuit. Report Instructions Besides the general guidelines, report the following for this lab: The lab report should be segmented into 3 parts: o Inverting amplifier o Non-inverting amplifier o Differentiator amplifier Each part should be comprised of o the circuit design with LTspice Capture and the simulated voltages at each node as well as the closed-loop gain, the analytical equation for each amplifier and the calculated output voltage and gain, the experimental voltage readout with a description of the experimental procedure , a table of all three values for the op-amp terminal voltages: from simulation, theory, and experiment, a table of all three values for the closed-loop op-amp gain seen by V3: from simulation, theory, and experiment, and your explanation of the variations between the three values of the last two steps. Answer the questions in the Analysis section References http://www2.cose.isu.edu/~chiustev/courses/EE4429/LTspice_Basics.pdf http://classes.engineering.wustl.edu/jee2330/Exp09.pdf http://www.muratpeker.com/files/elolab_2.pdf http://www.ti.com/lit/an/sboa092a/sboa092a.pdf