What Are Band-Pass Filters?

A band-pass filter is a device that allows waves of a specific frequency band to pass while shielding other frequency bands. For example, the RLC oscillation circuit is an analog band-pass filter. ^[1]

Bandpass filter

A bandpass filter is one that can pass through a certain frequency range.

An ideal band-pass filter should have a completely flat passband without amplification or attenuation in the passband.

Many audio equipment's spectrum analyzers use this circuit as a band-pass filter to select signals in different frequency bands, and use the number of light-emitting diodes on the display to indicate the size of the signal amplitude. The center frequency of this active band-pass filter, the voltage gain Ao = B3 / 2B1 at the center frequency fo, the quality factor, and the 3dB bandwidth B = 1 / ( * R3 * C) can also be determined according to the design Q, fo, Ao values to find the parameter values of each element of the band-pass filter. R1 = Q / (2foAoC), R2 = Q / ((2Q2-Ao) * 2foC), R3 = 2Q / (2foC). In the above formula, when fo = 1KHz, C takes 0.01Uf. This circuit can also be used for general frequency selective amplification. Active band-pass filter circuit

This circuit can also use a single power supply, just bias the positive input of the op amp at 1 / 2V + and connect the lower end of the resistor R2 to the positive input of the op amp.