Experiment on Simple Op-Amps

One of the purposes of this course is to demonstrate the utility of electronics. As a step toward this we want you to use the power supply you built in the previous experiment to power the following op-amp circuits.

(The 741 op-amps you are using have the following pin-outs: V⁺,V^-,V_out are pins 2, 3 and 6, respectively. To power the circuit, apply the positive side of your power supply to pin 7 of the op-amp, and the negative side of your supply to pin 4. This provides the DC bias current necessary to power the op-amp circuits you are about to build.

1.

Set up your op-amp as a comparator. To do this, ground V^-, and apply the following signal to the input $V_{in}=1.0sin(2\pi 100t)$intoV⁺. Sketch the output and the input versus time.

2.

Using resistors design and construct a noninverting op-amp amplifier with a voltage gain of 11 at a signal frequency of 100Hz. Set the amplitude of the input signal to approximately 0.1V. The resistor values you use should be aimed at being appropriate for currents in the one milliamp range. (The 741 op-amps you are using have the following pin-outs: V⁺,V^-,V_out are pins 2, 3 and 6, respectively. To power the circuit, apply the positive side of your power supply to pin 7 of the op-amp, and the negative side of your supply to pin 4. This provides the DC bias current necessary to power the op-amp circuits you are about to build. (BEFORE DOING THIS, MAKE SURE YOUR POWER SUPPLY IS WORKING PROPERLY BY SHOWING IT TO YOUR TA.)

3.

After you achieve the 11 voltage gain, increase the input signal amplitude to about 2 volts. What happens? What is your maximum input voltage before clipping occurs?

4.

Return the input voltage back to approximately 0.1V amplitude. Increase the frequency taking a data point at each decade starting at 100Hz, until your input signal is 1MHz. What happens to your gain as a function of frequency, do you know why?

5.

Using the discussion and equations in the previous section  , develop a method to to show that the output resistance of the noninverting op-amp is virtually zero. (Hint: Determine the output voltage and current for a series of load resistors ranging from 1K to 100K, and then use equation (1.13).

6.

Using the discussion and equations in section  , develop a method to to show that the input resistance of the noninverting op-amp is virtually infinity.

7.

Using resistors, design an inverting op-amp amplifier with a voltage gain of -10 at a signal frequency of 100Hz. Steadily increase the frequency of your input signal to 1MHz, taking a data point at each decade. What happens to your gain and why?

8.

Theoretically determine and also measure the input resistance of your circuit. Does your measured value agree with theory?

9.

Since the output of the inverting amp looks identical to the output of the noninverting amp, its output resistance should be approximately the same, ie, virtually zero. Using methods developed above, show that this is true.