Band Pass Filter
Band-Pass Filter is a circuit that is designed only to pass signals within a certain frequency band and to hold out signaling pathway that frequency band. This type of filter has a maximum output voltage at a particular frequency called the resonant frequency (ωr) If the frequency change of the resonant frequency of the output voltage goes down, there is a frequency above the resonance frequency (ωr) and one below (ωr) which remain gainnya 0.707 Ar . This frequency is marked (ωh) upper cutoff frequency and (ωl) below the cutoff frequency. Frequency band between (ωh) and (ωl) is the band width (B).
B = ωh – ωl
Band-pass filter is classified as a narrow band or wideband. Narrow band filter is a filter that has the band width is smaller than a tenth of its resonance frequency (B <0.1 ωr). if the band width is larger then a tenth of the resonant frequency (B> 0.1 ωr), the filter is a wideband filter. Comparison between resonant frequency and bandwidth are known as quality factor (Q) of the circuit. Q shows the selectivity of the circuit, the higher the Q value the more selective the filter circuit.
Q = ωr / B
B = ωr / Q
To fiter-narrow band filters, the Q of the circuit is greater than 10 and for wideband filters Q is smaller than 10. Band-pass filter arranged to filter high-pass and low-pass filter as shown below:
Values above the cutoff frequency is determined by high-pass filter as follows:
FCH = 1 / 2πRC
and lower cutoff frequency is determined by the low-pass filter as follows:
fcl = FCH = 1 / 2πRC
so the amount of bandwidth is:
B = FCH – fcl
Characteristics of band-pass filter is shown in the figure below: