LAB_20 - Op Amps - Lab 20 Operational Amplifiers...

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Lab 20 221 Operational Amplifiers Summary The operational amplifier is the most common analog integrated chip in electronic circuits today. Its wide range of applications includes such things as inverting and non-inverting amplifiers, buffer amplifiers, integrators, differentiators, signal generators and Schmidt triggers. Educational Objectives After completing this lab, the student should be able to: 1. Use an op-amp chip to build either an inverting or a non-inverting amplifier. 2. Choose resistors to design any desired gain factor. 3. Measure the gain of an op-amp circuit. 4. Find the linear region of an amplifier and identify where saturation sets in. "Every great advance in science has issued from a new audacity of imagination." - John Dewey
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Lab 20 222 Background Information The operational amplifier is an analog device which was developed in the 1940’s for use in analog computers. This fundamental electronic building block was called an operational amplifier because it was originally intended to perform mathematical operations such as addition and subtraction. In a sense the op-amp was the first analog computer. Once hard-wired, it could perform a single computation. It could not be programmed for any other computation except by rewiring the circuit. The standard symbol for an op-amp is shown in the figure to the left below. Bipolar Supply - The Op-Amp has a single output terminal and two input terminals, one of which is inverted (–) and one which is not. The two power terminals labeled ± V h ighlight the fact that the op-amp is an active device requiring an independent power source in addition to the two inputs. Notice that the op-amp requires two DC supply voltages, one at + V and one at – V . Both voltages can be delivered by using a bipolar power supply or a voltage divider. This use of bipolar supply voltages is to allow the amplified output voltage to swing in both positive and negative directions, as would be required in the amplification of AC signals. Figure 1a - Standard Op-Amp Symbol. Figure 1b - Op-Amp symbol including bipolar supply. Standard IC Packages - The original op-amps used vacuum tubes, dan- gerously high voltages and were very expensive. Today, high quality op- amps are available as inexpensive integrated circuit packages which oper- ate on moderate to small voltages. The 741 op-amp is available in both 8 pin and 14 pin Dual In-Line packages as well as 8 pin tin cans. The extra pins on the 14 pin chips are used for heat sinking, and can provide greater power.
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Lab 20 223 Pin Connections - In this lab we will be using an 8-pin 741 op-amp as shown above. The actual chip is smaller than your smallest fingernail. The pins are labeled from 1 to 8 with pin 1 to the left of the small notch as shown below. Notice that the two inputs are connected to pins 2 and 3. Pin 2 is the inverted input and pin 3 is the non-inverting input. The output is at pin 6. The bipolar power leads are connected to pins 4 and 7 as indi- cated. Pins 1 and 5 can be used to offset any null voltage which can arise due to variations between the
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LAB_20 - Op Amps - Lab 20 Operational Amplifiers...

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