5.6: Procedure

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1. The voltage gain of the inverting amplifier can be determined accurately from the feedback resistors \(R_i\) and \(R_f\). Calculate the voltage gains for the amplifier of Figure 5.5.1 for the \(R_f\) values specified, and record them in Table 5.7.1.

2. Assemble the circuit of Figure 5.5.1 using the 4k7 \(\Omega\) resistor.

3. Set the generator to a 1 kHz sine wave, 100 millivolts peak.

4. Apply the generator to the amplifier. Measure and record the output voltage in Table 5.7.1, noting its phase relative to the input. Also, compute the resulting experimental voltage gain and gain deviation.

5. Repeat step 4 for the remaining \(R_f\) values in Table 5.7.1.

6. For any given \(R_i\), \(R_f\) combination, the voltage gain should be stable regardless of the precise op amp used, even if it is of an entirely different model. To verify this, first set \(R_f\) to 22k \(\Omega\).

7. Set the generator to a 1 kHz sine wave, 100 millivolts peak.

8. Apply the generator to the amplifier. Measure and record the output voltage in Table 5.7.2. Also, compute the resulting experimental voltage gain and gain deviation.

9. Repeat step 8 for two other op amps.

10. The concept of virtual ground is very important. A virtual ground exists at the inverting input of the op amp in this circuit. Ideally, the voltage at this point should be very close to 0. Through voltage divider effect, this implies that all of the input signal must be dropping across \(R_i\), and thus \(R_i\) must establish the input impedance of the amplifier.

11. Set \(R_f\) to 4k7 \(\Omega\).

12. Set the generator to a 200 Hz sine wave, 1 volt peak.

13. Apply the generator to the amplifier. Use a DMM to measure and record the AC potential at the inverting terminal of the op amp. Record the value in Table 5.7.3.

5.6.1: Computer Simulation

14. Build the circuit in a simulator and run a Transient Analysis echoing steps 2 through 5. Compare the results to the waveforms generated experimentally.

15. Repeat step 14 but this time use the Distortion Analyzer instrument to compare voltage gain to THD.