# 11.5.6: Procedure

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1. This circuit can be examined through the use of the Superposition Theorem. The contribution of each input can be measured individually, combined, and then compared with common-mode and differential inputs.

2. Calculate the differential voltage gain for the amplifier and record it in Table 6.7.1

3. Assemble the circuit of Figure 6.5.1. Try to get the $$R_i/R_f$$ ratio as close as possible to the $${R_i}’/{R_f}’$$ ratio, even if you have to mix and match several resistors.

4. Set the generator to a 1 kHz sine wave, 500 millivolts peak.

5. Apply the generator to the $$V_{inv}$$ input, and ground the $$V_{non}$$ input.

6. Measure and record the output voltage in Table 6.7.2, noting the phase relative to the input. Also, compute the resulting voltage gain.

7. Swap the inputs by connecting the $$V_{non}$$ input to the generator, and grounding the $$V_{inv}$$ input.

8. Measure and record the output voltage in Table 6.7.2, noting the phase relative to the input. Also, compute the resulting voltage gain.

9. Compare the results of step 6 to step 8. The gains should be identical except that one is inverting while the other is non-inverting. Calculate the results of adding the two output signals and place the values in Table 6.7.3.

10. To measure the common-mode gain, connect both inputs to the generator (removing the $$V_{inv}$$ ground). Record the output voltage and resulting gain in Table 6.7.3.

11. Assemble the circuit of Figure 6.5.2. Adjust the potentiometer to set the voltage gain to precisely –1. This circuit is a simple phase-splitter and is used to generate a differential input signal.

12. Connect the circuit of Figure 6.5.2 to the original circuit as shown.

13. Measure and record the output voltage in Table 6.7.3.

14. Based on the results of Table 6.7.3, compute the experimental common-mode rejection ratio and place it in Table 6.7.4.

11.5.6: Procedure is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by James M. Fiore.