# 2.6: Procedure

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## 2.6.1: DC Parameters

1. Assume that the transistors of Figure 2.5.1 have a current gain of 150. Calculate the base currents and collector voltages for the amplifier of Figure 2.5.1 and record them in Table 2.7.1. Also, compute and record the theoretical (ideal) input offset current and output offset voltage.

2. Assemble the circuit of Figure 2.5.1.

3. Measure and record the base currents in Table 2.7.1. (Note: You may wish to measure the voltage across the base resistors and compute the base currents if the DMM cannot measure small DC currents.) Based on these currents, compute and record the experimental input bias and offset currents along with the corresponding deviations.

4. Measure and record the collector voltages in Table 2.7.1. Based on these voltages, compute and record the experimental output offset voltage and the corresponding deviation.

## 2.6.2: AC Parameters

5. Calculate the differential voltage gain and collector voltages for the amplifier of Figure 2.5.2 using an input of 20 millivolts, and record them in Table 2.7.2.

6. Assemble the circuit of Figure 2.5.2.

7. Set the generator to a 1 kHz sine wave, 20 millivolts peak.

8. Apply the generator to the amplifier. Measure and record the AC collector voltages in Table 2.7.2 while noting the phase relative to the input. Also, compute the resulting experimental voltage gain from the input to collector one, and the deviations.

9. Apply the generator to both inputs. Set the generator’s output to 1 volt peak.

10. Measure the AC voltage at collector one and record it in Table 2.7.3.

11. Based on the value measured in step 10, compute and record the common-mode gain and CMRR in Table 2.7.3.

## 2.6.3: Improved CMRR

12. Assemble the circuit of Figure 2.5.3. This circuit uses an improved tail current source that exhibits much higher internal impedance than the circuit of Figure 2.5.2. This should yield a decrease in common mode gain which, in turn, should yield an improved CMRR. Note that the new circuit sets up virtually the same tail current, therefore producing approximately the same DC parameters and differential gain as the original.

13. Repeat steps 9 through 11 recording the results in Table 2.7.4.

## 2.6.4: Troubleshooting

14. Continuing with the amplifier of Figure 2.5.3, turn the signal down to 0. Estimate and then measure the results for each individual error presented in Table 2.7.5.

## 2.6.5: Computer Simulation

15. Build the amplifier of Figure 2.5.2 in a simulator and run a Transient Analysis echoing steps 5 through 8. Compare the results to the data found in Table 2.7.2.

This page titled 2.6: Procedure is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by James M. Fiore via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.