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ECE 252 Introduction to Electrical Engineering Lesson 13A. Operational Amplifiers Homework Version S16 Homework partner name: _______________________Homework partner name: ________________________ 1. Quickies: a) To operate correctly, op-amps need power from two supply voltages that are ______________ in magnitude and ___________________ in sign. b) A typical op-amp might have a(n) ___________________ impedance exceeding 1 MΩ. c) Circle the most likely value for the voltage gain of a typical op-amp: 1; 10; 500; 25,000; 1,000,000 d) When calculating vp for an ideal op-amp, assume that no current flows into the __________________ input. e) When calculating vn for an ideal op-amp, assume that it is equal to ____________________. f) When applying Kirchhoff’s Current Law at the negative input of an ideal op-amp, assume that no current flows into the ___________________ input. g) The __________________ of real op-amps tends to decrease as the frequency increases. h) When using an op-amp as a differential amplifier, it is wise to select one with a high _____________________________________________ . Signatures: ________________________________________________________________________ 2. Design an op-amp circuit using the circuit below. It must have a gain of -20 and produce an output of -12 V. Available devices: an ideal op-amp, a .6 V battery, a 1 V battery, a 1.5 V battery, and the following resistors: 10 kΩ, 15 kΩ , 30 kΩ, 80 kΩ, 120 kΩ, 150 kΩ, 240 kΩ, 300 kΩ, 500 kΩ. Completely label the circuit. Carefully show your analysis of the circuit, using the assumptions for an ideal op-amp, to prove that your circuit gives the desired output. It is not necessary to use all of the available devices. Signatures: ________________________________________________________________________ 3. For the circuit of Problem 2, select appropriate power supplies for the op-amp. You are not limited to the batteries in Problem 2. Explain your choice. Signatures: ________________________________________________________________________ 4. E1 = 5 V. R1 = 33 kΩ. R2 = 470 kΩ. Completely label the circuit. Carefully show your analysis of the circuit, using the assumptions for an ideal op-amp. Find vo. Signatures: ________________________________________________________________________ 5. E1 = 4 V. E2 = 5 V. E3 = 6 V (note the orientation of E3). R1 = 100 kΩ. R2 = 80 kΩ. R3 = 50 kΩ. RF = 220 kΩ. Label the circuit as appropriate. Carefully show your analysis of the circuit, using the assumptions for an ideal op-amp. Find vo. The answer is not an integer. It is a positive number between 1 V and 10 V. Signatures: ________________________________________________________________________ 6. Below is a model of a differential amplifier. vs is a small signal from a sensor; it's perhaps a few millivolts. The vx voltage represents noise that might contaminate the output; it could be a few tens of volts. The purpose of this differential amplifier circuit is to amplify the sensor voltage while rejecting the noise voltage. R1 = R2 = 4 kΩ. RF = R3 = 96 kΩ. Label the circuit as appropriate. Carefully show your analysis of the circuit, using the assumptions for an ideal op-amp. Find vo as a function of vx and vs. The result will be an integer multiple. Be careful not to round off values until your final calculation. Hints: Carefully determine the voltage above the vs source (it is not vs). Try using a voltage divider to find vp. Put your solution here. Signatures: ________________________________________________________________________ BONUS (No partial credit). R1 = 10 kΩ. R2 = 120 kΩ. R3 = 12 kΩ. R4 = 100 kΩ. vin = .05 V. Carefully show your analysis of the circuit, using the assumptions for an ideal op-amp. Calculate the output voltage vo. Signatures: ________________________________________________________________________ © 1998-2016 Thomas G. Cleaver. All rights reserved.