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Unformatted text preview: Circuits Lab VI: Op-Amp Pre-lab Name: __________________________________________ EID: _____________ By placing my name and EID above, I am certifying that I determined the answer to the questions posed below and did not copy my answers from a fellow student. *** Due at the beginning of your lab session *** Background An op-amp is an analog integrated circuit available in a wide variety of packages. The name operational amplifier comes from the days of analog computers in which analog circuits were used to perform various functions such as inversion, multiplication, integration, and division. Op-amps today are used in a tremendous number of analog circuit designs ranging from audio amplifiers to filters to instrumentation. The focus in this laboratory will be on the DC behavior of an op-amp in an inverting amplifier configuration. You will learn about the AC behavior of an op-amp in EE 411, Circuit Theory. To begin, lets examine a typical specification for one of the most popular operational amplifiers: the 741. National Semiconductor is one manufacturer of the 741 and they supply a detailed specification as shown starting on page 4. From the specification sheet we can learn how the device will perform, how it is packaged, and its limitations. For example, the first page of the 741 product specification shows the pin configuration for the 8 pin dual-in-line package (DIP). The 741 is limited to maximum supply voltages of 22 Volts. To get a sense of what makes up an integrated op-amp, refer to the schematic diagram of the product specification. We can see that the chip inside the 8 pin package consists of many transistors and resistors. All of this can be purchased for around 25 cents. The specification also shows that devices of different tolerances are available (LM741A, LM741, LM741C). The 741C is usable in a wide variety of applications where slightly lower performance is acceptable. With this lower performance comes somewhat lower cost. An operational amplifier can be characterized by the equation: ( ) + = V V A V out (1) where A is the open-loop gain, V + is the non-inverting input voltage, and V- is the inverting input voltage. In many op-amps, A can range from 10,000 to 20,000,000. For the 741, we can find the range of values by examining the Large Signal Voltage Gain specification. For the 741, the minimum large signal voltage gain is given as 50 V/mV (50,000) and the typical value is 200 V/mV (200,000) at an ambient temperature of 25 o C, supply voltages of 15V, load resistor of at least 2 k and output voltages 10V. Across the specified Circuits Lab VI - Operational Amplifiers 1 temperature operating range, the minimum is guaranteed to be 25 V/mV (25,000). If the op-amp gain is 25,000, and V- is connected to ground, a 0.2 mV signal on the V + input would produce an output voltage of 5V....
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This note was uploaded on 11/30/2010 for the course EE 302 taught by Professor Mccann during the Spring '06 term at University of Texas at Austin.
- Spring '06