8.6: Procedure

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1. The upper break frequency, \(f_2\), of the amplifier in Figure 8.5.1 can be determined from its voltage gain and the \(f_{unity}\) of the op amp. Calculate the \(f_2\) values for the amplifier of Figure 8.5.1 for the \(R_f\) values specified, and record them in Table 8.7.1.

2. Assemble the circuit of Figure 8.5.1 using the 4k7 \(\Omega\) resistor.

3. Set the generator to a 100 Hz sine wave.

4. Apply the generator to the amplifier and adjust its level to achieve a 5 volt peak signal out of the op amp. Measure the input voltage and compute the resulting voltage gain. Record this voltage gain in Table 8.7.1.

5. Increase the frequency until the op amp’s output voltage drops 3 dB (i.e., to 0.707 times 5 volts peak). Record this frequency in Table 8.7.1 as the experimental \(f_2\).

6. Compute the experimental \(f_{unity}\) by multiplying the experimental voltage gain by the experimental \(f_2\), and enter this value in Table 8.7.1.

7. Repeat steps 3 through 6 for the remaining \(R_f\) values in Table 8.7.1. Note that the values in the experimental \(f_{unity}\) column should be consistent with the \(f_{unity}\) specified in the device data sheet.

8. An alternate method to determine \(f_2\) is to measure the rise time of an output square wave. To follow this method, first set the generator to a 1 kHz square wave.

9. Apply the generator to the amplifier and adjust its level to achieve a 2 volt peak signal out of the op amp. Measure the rise time and record this value in Table 8.7.2. An accurate measurement is important, so be sure to expand the time base so that the rising edge fills the majority of the oscilloscope display.

10. Use the rise time to compute the experimental \(f_2\), and record this value in Table 8.7.2.

11. Compute the experimental \(f_{unity}\) by multiplying the experimental voltage gain from Table 8.7.1 by the experimental \(f_2\) found in step 10, and enter this value in Table 8.7.2.

12. Repeat steps 9 through 11 for the remaining \(R_f\) values in Table 8.7.2. Note that the values in the experimental \(f_{unity}\) column should be consistent with those found in Table 8.7.1.

8.6.1: Computer Simulation

13. Build the circuit in a simulator and run an AC Analysis for each resistor listed in Table 8.7.1. Be sure to run the plot from 100 Hz to approximately \(f_{unity}\) and use a decibel scale for the gain amplitude. Record the simulation \(f_2\) results in Table 8.7.3 and compare them to the \(f_2\) values measured in Tables 8.7.1 and 8.7.2. Include the graph for the 4k7 with the technical report.