Lab 7 Operational Amplifiers. 

Outcome of this lab:
1. Be familiar with the parameters of an OpAmp.
2. Be able to use an OpAmp to amplify a small signal.
3. Be able to use the function generator, the oscilloscope, and the power supply for circuit testing.

We'll use LM741 for this lab.

The pin map of LM741 is:

The functions of the pins are:

Complete the following tasks: 

Task 1:
Build the following circuits on a breadboard and fill up the table with the data you observed. Explain why Vp=Vm or Vp!=Vm accordingly.

Task 2:

On Page 4 of the datasheet, find the maximum supply voltage and the input voltage that can be applied to the device. Make a screen shot of it and show it on your report.

Task 3:

Connect your OpAmp with a R1=5k resistor and a potentiometer (100k). Power up your OpAmp using +9V/-9V instead of 9V/GND. Connect the input signal to a sine wave (1k Hz, 2V Vpp). Change the resistance of the potentiometer while you are looking at the scope.

Report the maximum amplification that can be used for this topology. (show the input and output in the oscilloscope at the same time, use cursors to measure the voltage output and save the result in your USB drive).

Use another potentiometer (1 Mohm) to amplify a 2 mV, 1 kHz sine wave and report the results in the same way.

Repeat step 2 using the following circuit.

Task 4:

Change the -9V supply back to GND. Use a voltage divider to provide 4.5 DC 'bias voltage' to the non-inverting terminal.
Add an 'DC offset voltage' to the singal from the function generator (sine wave, 1 kHz, 2V Vpp), this 'offset voltage' should be equal to the DC voltage at the non-inverting terminal.

Try different potentiometers and test what is the maximum amplification you can achieve. (if the signal is out of the screen on the oscilloscope, push 'channel 1 menu', then select 'AC' for the 'Coupling' option).

Change the DC offset voltage to 0V and see if you can still see the signal? Why or why not?

Task 5:

Remove the feedback resistor and R1. Inject a triagle wave (10V Vpp, 1 kHz) into the inverting terminal. Show the input and output of the OpAmp at the same time in the scope. Measure the voltage point that triggers the changes of the output and explain if this makes sense. Report the scope results. (Please note that the resistance change in the voltage divider. Please change the DC offset for the inverting terminal accordingly).

----------------the end of the lab