# 20.6: Procedure


## 20.6.1: Low Pass Filter

1. The circuit of Figure 20.5.1 is a second order low pass filter. Calculate and record the corner frequency $$(f_2)$$ and mid-band voltage gain in Table 20.7.1.

2. Assemble the circuit of Figure 20.5.1.

3. To measure the mid-band voltage gain, set the generator to a 1 volt sine wave at about one decade below $$f_2$$. Measure the output of the filter and calculate the voltage gain. Record this in Table 20.7.1.

4. While monitoring the filter output with the dB meter, sweep the generator frequency about $$f_2$$ until the output has fallen 3 dB from its mid-band value. Record this frequency in Table 20.7.1.

5. In Table 20.7.2, record the dB gain of the filter at 5 frequencies between 0.1 $$f_2$$ and $$f_2$$, and at 5 frequencies between $$f_2$$ and 10 $$f_2$$. Using these data, create a semi-log plot of the frequency response of the filter. Note, it may be convenient when graphing if at least some of these frequencies are simple octaves apart, such as 5 $$f_2$$ and 10 $$f_2$$.

6. Do not disassemble the circuit.

## 20.6.2: High Pass Filter

7. The circuit of Figure 20.5.2 is a second order high pass filter. Calculate and record the corner frequency $$(f_1)$$ and mid-band voltage gain in Table 20.7.3.

8. Assemble the circuit of Figure 20.5.2.

9. To measure the mid-band voltage gain, set the generator to a 1 volt sine wave at about one decade above $$f_1$$. Measure the output of the filter and calculate the voltage gain. Record this in Table 20.7.3.

10. While monitoring the filter output with the dB meter, sweep the generator frequency about $$f_1$$ until the output has fallen 3 dB from its mid-band value. Record this frequency in Table 20.7.3.

11. In Table 20.7.4, record the dB gain of the filter at 5 frequencies between 0.1 $$f_1$$ and $$f_1$$, and at 5 frequencies between $$f_1$$ and 10 $$f_1$$. Using these data, create a semi-log plot of the frequency response of the filter.

## 20.6.3: Band Pass Filter

12. Cascade the high pass and low pass filters.

13. Take several gain readings on both sides of $$f_1$$ and $$f_2$$, and record these in Table 20.7.5. Again, using these data, create a semi-log plot of the frequency response of the filter.

## 20.6.4: Computer Simulation

14. Build the circuit of Figure 20.5.1 in a simulator and run an AC Analysis. Be sure to run the plot from 100 Hz to approximately 100 kHz and use a decibel scale for the gain amplitude. Compare the plot to the graph generated from Table 20.7.2.

This page titled 20.6: 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.