# Homework 13A

```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.