Bandpass filter operating principle and detail of bandpass filter schematic

A band-pass filter is a device that allows waves in a specific frequency band to pass through while shielding other frequency bands. For example, the RLC tank is an analog bandpass filter.

A band-pass filter is a filter that passes a frequency component in a certain frequency range but attenuates other range frequency components to a very low level, as opposed to the concept of a band-elimination filter. An example of an analog bandpass filter is a resistor-inductor-capacitor circuit (RLC circuit). These filters can also be generated by combining a low-pass filter with a high-pass filter.

working principle

An ideal band-pass filter should have a perfectly flat passband with no amplification or attenuation within the passband and all frequencies outside the passband are completely attenuated. In addition, the out-of-band conversion is minimal. The frequency range is complete.

In fact, there is no ideal bandpass filter. The filter is not able to completely attenuate all frequencies outside the desired frequency range, especially outside the desired passband, and there is also a range that is attenuated but not isolated. This is commonly referred to as the roll-off phenomenon of the filter and is expressed in terms of the number of decibels per decade of attenuation. In general, the design of the filter ensures that the narrower roll-off range is as good as possible, so that the performance of the filter is closer to the design. However, as the roll-off range becomes smaller and smaller, the passband becomes flatter and starts to appear "rippled." This phenomenon is especially noticeable at the edges of the passband. This effect is called the Gibbs phenomenon.

In addition to electronics and signal processing, an example of a bandpass filter application is in the atmospheric sciences. A common example is the use of a bandpass filter to filter weather data over the last 3 to 10 days. Only the disturbed cyclone remains in the domain.

Between the lower frequency shear frequency f1 and the higher shear frequency f2 is the resonant frequency, where the filter gain is maximum and the filter bandwidth is the difference between f2 and f1.

typical application

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

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

Bandpass Filter Schematic R1 value is determined in advance in this circuit, its size is similar to the signal source resistance r1 / parameter selection principle is R4 = R3, C1 is approximately equal to C2, Q is less than or equal to R1,500K "R" 1K, 0.5uF "C" 200pF.

Bandpass filter schematic

In this circuit, the value of R1 is determined in advance, and its size is similar to the signal source internal resistance r1. The principle of parameter selection is R4=R3, C1 is approximately equal to C2, and Q is less than or equal to R1,500K, "R"1K, and 0.5uF"C"200pF.