• To investigate the design for inverting and non-inverting operational amplifiers.

1 - Heathkit Circuit Design Trainer (CDT)

1 - Digital Mulitmeter (DMM)

1 – Oscilloscope (Scope)

1 – Function Generator (FG)

1 – 741 op-amp IC

Various ¼ W resistors for amplifier design

Miscellaneous leads and connectors

The objective for this lab was to investigate the design of the inverting and non-inverting operational amplifier (op-amp). Before the lab was performed a small amount of information about the ideal op-amp was given. An ideal op-amp has infinite gain, infinite impedance and zero output impedance. With the development of integrated circuit technology, current state-of –the-art op-amps very nearly reach this ideal. In this lab, only gain and input impedance will be controlled by design. The inverting and non-inverting op-amps are shown in Figure 1.

In the first procedure we were to design an inverting op-amp circuit using the 741 op-amp to have a closed circuit voltage gain of -10. We were also to measure and record the values of Ri, Rf and to determine if our circuit would have a voltage gain (Av) equal to /or approximately equal to -10.

Table 1.Ri, Rf and Av values for

In the second procedure we were to set up the circuit we designed on the CDT. We connected +Vcc and -Vcc to the +12V and –12V supplies respectively. The sketch for the circuit is on the lab data sheet.

In the third procedure we were to check the input voltage of the amplifier and output voltage and see if they set to zero. Our analysis shows that our Vin = 0.145 V and our Vout = -1.485 V, which is acceptable due to the variability in the accuracy of the equipment used for this lab.

In the fourth procedure we were to apply a series of voltages less then 1 Volt (DC) to the circuit. The voltage gain (Av) was to be determined and compared to the design value. The equation used to determine the Av is: Av = Vout/Vin = -Rf/Ri .We were to use two positive and two negative values for the input voltage. These values and their respective results are found in Table 2. A second part of procedure four required us to create a sine wave (amplitude < 1V, and frequency of 1 kHz.) for the op-amp circuit. Additionally, we were to then increase the amplitude and observe and record any distortions in the output voltage (Vout). As we increased the amplitude, the sine wave for Vout began to reach the saturation voltage (Vsat) limit. This caused the sine wave to be "chopped" at the peaks. We were then to set the amplitude < 1V and frequency = 1Khz and then increase the frequency to a frequency greater than 10 kHz. We were then to adjust the scope settings so we could observe and record any distortion in Vout. We observed a noticeable distortion at a frequency of 45.4545 kHz. The graphical representations are found on the data sheet as 4.2.a, 4.2.b, and 4.2.c respectively.

Vin	Vout	Av = Vout/Vin
0.500 V	-5.262 V	-10.524
0.745 V	-7.800 V	-10.469
-0.675 V	7.240 V	10.726
-0.822 V	8.890 V	10.815

Table 2. Input/Output voltages and Voltage

In the fifth procedure we were to repeat procedures 1 through 4 for the non-inverting op-amp. The graphical representation of the circuit is found on the data sheet. The values are recorded in Table 3. The only difference is that here the equation to calculate the experimental Av is: Av = Vout/Vin = 1 + (Rf/Ri). This value was calculated to be 11.63.

Vin	Vout	Av = Vout/Vin
0.584 V	6.814 V	11.667
0.904 V	10.570 V	11.692
-0.365 V	-4.260 V	11.671
-0.804 V	-9.360 V	11.642

This lab was designed to challenge the student’s knowledge of the use of the CDT, oscilloscope, and the DMM. The lab introduced the op-amp chip, which the students were required to wire into a circuit in the configurations of the inverting and non-inverting amplifiers. This lab served to increase our knowledge of basic lab equipment and circuit analysis concepts learned in the classroom. It provided a "real-world" application to these concepts, thus assisting in the study and comprehension of the material introduced in this course.