A Band-Pass Filter is a circuit that only allows a certain range or band of frequencies to pass, while attenuating or rejecting signals whose frequencies are either below a lower cut-off frequency or above an upper cut-off frequency.
A simple band-pass filter may be obtained by combining a low-pass filter and a high-pass filter.
The range of frequencies that a band-pass filter allows to pass is referred to as the 'passband'.
The band-pass filter is the opposite of the band-stop filter.
An ideal band-pass filter is one whose passband doesn't undergo any change (i.e., no gain nor attenuation), but completely rejects all frequencies outside the passband.
In an ideal band-pass filter, the transition of the response from outside the passband to within the passband and vice versa is instantaneous.
Of course, an ideal band-pass filter doesn't exist in the real world, i.e., some attenuation still occurs within the passband while complete attenuation is not achieved outside the passband.
The amount of attenuation outside the passband may be described in terms of the 'roll-off' of the filter, which is the attenuation in dB per octave of frequency.
LC band-pass filters, or filters containing resonant circuits composed of inductors and capacitors, has a resonant frequency between the lower cut-off frequency f1 and the upper cut-off frequency f2.
At this resonant frequency, the gain of the band pass filter is at its maximum.
The over-all impedance of a resonant series LC circuit consisting of an inductor and a capacitor in series with each other will drop to zero at the resonant frequency because the reactances of the inductor and the capacitor cancel each other out under resonance.
On the other hand, the over-all impedance of a resonant parallel LC circuit consisting of an inductor and a capacitor in parallel with each other will increase to infinity at the resonant frequency, i.e., the reactances of the inductor and the capacitor result in zero current flow under resonance.
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A Band-Pass Filter is a circuit that only allows a certain range or band of frequencies to pass, while attenuating or rejecting signals whose frequencies are either below a lower cut-off frequency or above an upper cut-off frequency.
A simple band-pass filter may be obtained by combining a low-pass filter and a high-pass filter.
The range of frequencies that a band-pass filter allows to pass is referred to as the 'passband'.
The band-pass filter is the opposite of the band-stop filter.
An ideal band-pass filter is one whose passband doesn't undergo any change (i.e., no gain nor attenuation), but completely rejects all frequencies outside the passband.
In an ideal band-pass filter, the transition of the response from outside the passband to within the passband and vice versa is instantaneous.
Of course, an ideal band-pass filter doesn't exist in the real world, i.e., some attenuation still occurs within the passband while complete attenuation is not achieved outside the passband.
The amount of attenuation outside the passband may be described in terms of the 'roll-off' of the filter, which is the attenuation in dB per octave of frequency.
LC band-pass filters, or filters containing resonant circuits composed of inductors and capacitors, has a resonant frequency between the lower cut-off frequency f1 and the upper cut-off frequency f2.
At this resonant frequency, the gain of the band pass filter is at its maximum.
The over-all impedance of a resonant series LC circuit consisting of an inductor and a capacitor in series with each other will drop to zero at the resonant frequency because the reactances of the inductor and the capacitor cancel each other out under resonance.
On the other hand, the over-all impedance of a resonant parallel LC circuit consisting of an inductor and a capacitor in parallel with each other will increase to infinity at the resonant frequency, i.e., the reactances of the inductor and the capacitor result in zero current flow under resonance.
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