EET2222 -- Electronic Devices and Circuits Lab

Lab 13 – Comparators and Summing Amps

Reference: Floyd, Section 13-1 and 13-2

Figure 1

The pin diagram for the 741 operational amplifier is shown in Figure 1. This lab deals with two different circuits.

1. Comparator

Figure 2

A. Set up the circuit in Figure 2. This circuit is known as a noninverting comparator since it will detect the polarity of the input signal. Sketch or print your input and output signals showing the phase relationship (label axis with units and calibration points). Answer the following questions:

What is the polarity of the output voltage relative to the input signal?

What are the maximum output (saturation) voltages (both positive and negative)?

B. Reverse the input connections so the function generator input is connected to the inverting input and the noninverting input is grounded. Sketch or print your input and output signals showing the phase relationship (label axis with units and calibration points). Answer the following questions:

What is the polarity of the output voltage relative to the input signal?

What is the difference between the operation of this circuit and that used in step A?

2. Summing Amplifier

A. To obtain voltages with different amplitudes, the voltage divider shown in Figure 3 is used. Calculate v1 through v4 based on ideal and actual resistor values. Build the voltage divider circuit, measure v1 through v4, and compare the measured results with your calculated values.

Figure 3

B. Set up the circuit in Figure 4. Use power supply voltages of ±12 volts DC. From the ideal and actual component values, determine the mathematical expressions for v_out in terms of the input voltages. Measure v_out and compare to the predicted values.

Figure 4

Your report is due at the end of the lab period. Please use the green engineering paper.