ECE 3235 Electronics II
Experiment # 3
Basic Application of OpAmp II
Note: you might want to bring a calculator to the lab
1. General Information
Figure 1 OpAmp 741 Pinout.
Figure1 shows the pin configuration for the famous 741 operational amplifier (OpAmp).
Note that there is no ground pin. As shown in figure 2, you must define ground as the
common connection between the positive and negative DC supplies, which will be ±15 V
throughout this and following experiments. This ground node must always be your
common ground for all instruments and elements in the circuit.
Figure 2 OpAmp 741 Pinout with Power Supply.
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2.The integrator circuit
Figure3 Integrator Circuit.
Construct the circuit of Figure 3. This is an inverting integrator if the frequency of the
input signal is “high enough.” To verify this, apply a 5-kHz 80mV (peak-to-peak) square
wave to the input and observe the output.
1) The theoretically expected slopes of the triangular output are (Vm/R*C, where Vm is
the peak value of the square-wave input. Are they?
2) What happens to the linearity of the output as the input frequency is decreased?
3) What is the function of R’ in this circuit?
Apply a low-frequency 10Hz 80mV (peak-to-peak) sinusoid to the input.
4) Measure the gain and phase shift at 10Hz. Are these values the same as those found
for the inverting amplifier in Lab 2?
5) Additionally, measure accurately the –3 dB frequency fc and the phase there, as well
as the gain and phase at 10fc and 20fc.
6) What is the high-frequency roll-off in dB/octave?
Finally, apply a 5-kHz triangular wave to the input.
7) Sketch on the same set of axes the input and output waveforms showing key amplitudes
and times.
8) What is the ratio of the peak-to-peak values of Vout and Vin?
9) What would be the theoretical ratio of Vout and Vin? Compare that to the value in 8).
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10) Remove the resistor R’, and apply a 50Hz, 500Hz, 5kHz and 50kHz sin wave input
(80mv peak-to-peak), and sketch on the same axes the input and output waveforms. Any
changes compared to the case without R’?
3. The differentiator circuit
Figure 4 Differentiator Circuit
Build the circuit of Figure 4. This is a differentiator circuit. Apply a 2V peak-to-peak
sinusoid wave at f1 = 100 Hz, f2 = 1 kHz, and f3 = 10 kHz to the input and observe the
output.
1) Measure the peak voltage at the output for each frequency.
2) Sketch the waveform for each frequency.
3) Find the frequency where the input and output are at the same level. What is their
relative phase (phase shift) at this point?
4) Repeat the above measurements for the differentiator using a 2V p-p triangular wave
at the same three frequencies.
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