What is BPF?
BPF or “band pass filter” is a device that allows the passage of frequencies of a certain desired range and rejects or blocks those that go below or above the particular range. This type of filtering mechanism can be achieved by using both low-pass filters and high-pass filters. In this simple setup, the low-pass filter will attenuate or block frequencies that are considered too high while the high-pass filter will block frequencies that are deemed too low.

Aside from the typical setup of combining the properties of low-pass and high-pass filters, BPF or band pass filters may also be created using inductors. This type of BPF is said to have an advantage in terms of design because of the reactive property of the capacitors involved. Regardless if the high-pass portion or the low-pass part comes first in the design, undesired frequencies that are too high and too low will still be filtered out and rejected.

Though the system of employing both the properties of low-band and high-band filters is effective in filtering out certain frequencies above and below the desired value, this concept also has its own limitations. One such limitation is that this setup allows for uninterrupted passage of frequencies within the desired range. While the two sections of low-pass and high-pass filters will successfully block undesired frequency levels, the result would be a decrease in amplitude or an attenuated signal even if the source voltage is at its highest. And this attenuation in signal gets even more obvious and noticeable if the filtering system is setup to be more selective, narrowing the band for desired frequencies. A common application of signal attenuation would be in lowering the volume of a particular stereo device. Once the sound volume is lowered, the amplitude is also lowered, and the signal being sent to the stereo speakers are also attenuated.