OPERATIONAL AMPLIFIERS LAB

OBJECTIVES

1. inverting amplifiers;
2. current to voltage converters;
3. integrators.

DISCUSSION

APPARATUS

• DC power supply with multiple outputs
• 741 operational amplifier integrated circuit chip
• oscilloscope
• prototype board, capacitors and resistors
• function generator

PROCEDURE

1. Connect a 741 operational amplifier as an inverting amplifier as given in figure 1.
   
   Note: The power supply has some ac ripple riding on the 15 V dc output. Measure the amplitude and the frequency of this noise from the dc supply. Note what it does to the input signal from the function generator. I tried various combinations of capacitors to get rid of this noise without much success. You will have to interpret the input and output signal on your oscillowscope by visually averaging out the noise. At the end of the experiment, explain why the noise isn't amplified.
2. use the function generator for the ac input and measure the input and output with the oscilloscope. Cover the frequency range 100 Hz to 100 kHz. Do this for two "gains" corresponding to R1 = 1kOhm, R2=10k, and R1=1k, R2=100k.
   
   You will need to keep the input signal low enough to prevent the output from being "clipped". Adjust the input and observe the output to see what is meant by clipping. Measure the peak to peak voltage and compare this to the power supply voltages. Explain.
3. Input and output impedances of the Op Amp.
   
   • The input impedance should be equal to R1. [Derive this in your lab later.] Measure the input impedance at 1 kHz. Hint: Use the variable resistance decade shown in the figure plus a DMM. First determine the approximate output impedance of the function generator. Then, determine the input impedance of the Op Amp.
   • Output impedances are normally low, say Z<1--10 Ohms, and therefore more difficult to measure precisely. Load the output of your inverting amplifier and measure the change in the output. Do not reduce the load below 1 Ohm!
4. Add a capacitor in parallel with R2. Select a value that gives you a corner frequency of 10kHz--30 kHz. Remeasure the gain as a function of frequency.
5. Graphically compare your measured values of gain to the theoretical values. Explain your results.

• A current to voltage converter;
• An integrating circuit;