Lab 7: The Op Amp Laboratory Objectives: 1) To introduce the operational amplifier or Op Amp 2) To learn the non-inverting mode 3) To learn the inverting mode 4) To learn the differential mode Before You Come to Lab: Download and read the LM741 Op Amp datasheet from http://www.ti.com/lit/ds/symlink/lm741.pdf Section 1: The Op Amp The Op Amp is an IC, or integrated circuit. An integrated circuit is a chip that groups components together in a commonly used application for simplicity. The LM741 is an amplifier circuit that has been placed inside an 8-pin chip. Package looks like: Internal Circuitry: Note: Use this dent to make sure the chip is right side up (Image Credit: http://en.wikipedia.org/wiki/file:generic_741_pinout_top.png )
The Power Supply: +5V, -5V and Ground Open the Power Supply Enable the fixed +5V supply (V+), which uses the V+ lead and it s corresponding GND lead ( ) Enable the fixed -5V supply (V-), which uses the V- lead and it s corresponding GND lead ( ) Use the Power button to turn both power supplies on and off
Section 2: Non-Inverting Mode Build the circuit shown below: Lead W1 Lead 2+ Lead 1+ W1 GND Lead 1- Lead 2- Use R 1 = 10kΩ and R 2 = 20kΩ NOTE: GND should be connected to both the ground from the +5V supply and the -5V supply, as well as the GND for W1, this ground should also be used as the reference for all measurements. Input Signal (V in): Use the function generator, WaveGen 1, and a 1kHz sine wave with a 0V offset (If needed, review Lab 5 for help with the function generator)
ADI Discovery Module: Use Scopes 1 and 2 to observe the input waveform and its corresponding output Record your results below: The gain of amplifier, or β, is the ratio of the output to the input. For the non-inverting mode this can be expressed as: Calculate β: Use β to explain your oscilloscope output:
Turn off all power and swap R1 and R2 Observe again and record the new result below: Calculate β: Use β to explain your oscilloscope output:
Section 3: Inverting Mode Build the circuit shown below: Lead 1+ Lead W1 Lead 2+ W1 GND Lead 1- Lead 2- Use R 1 = 10kΩ and R 2 = 20kΩ Input Signal (V in): Use the function generator, WaveGen 1, and a 1kHz sine wave with a 0V offset
ADI Discovery Module: Use Scopes 1 and 2 to observe the input waveform and its corresponding output Record your results below: The gain of amplifier for the inverting mode this can be expressed as: Calculate β: Use β to explain your oscilloscope output:
Turn off all power and swap R1 and R2 Observe again and record the new result below: Calculate β: Use β to explain your oscilloscope output:
Section 4: Changing the Gain 25.108 Intro To Engineering II for ECE: Lab 7 The Op Amp Sketch the following circuit: Using the inverting circuit from Section 3, add a 10kΩ potentiometer in series with R 1 Use R 1 = 10kΩ and R 2 = 20kΩ Sketch your circuit below and then construct it:
ADI Discovery Module: Use a 1kHz Sine wave with a 1V amplitude Use Scopes 1 and 2 to observe the input waveform and its corresponding output Record your results with the potentiometer turned all the way up and all the way down below: Calculate your range of gains (β): Use these gains to explain your oscilloscope output:
Section 3: Differential Mode Build the circuit shown below: Use R 1 = 10kΩ and R 2 = 20kΩ Use both function generators: V in- : 1kHz sine wave V in+ : 2kHz sine wave
ADI Discovery Module: Use the scopes to observe the output waveform with respect to each input wave form Record your results below: In differential mode the output voltage can be found with the following equation: Explain how this equation relates to your oscilloscope results: Explain what happens if V in+ = V in- :