Bandpass Filter
RC bandpass Filter
RC Bandpass Filter is a filter that allows a certain band of frequencies to pass through and attenuates all other frequencies below and above the passband. This passband is known as the bandwidth of the filter.
As seen, it is obtained by cascading a high-pass RC filter to a low-pass RC filter. It is shown in Figure (A) & (B) along with its response curve. The passband of this filter is given by the band of frequencies lying between fc1 and fc2. Their values are given by
The ratio of the output and input voltages is given by
………………… from f1 to fC1;
………………… from fC2 to f2
Series-Resonant Bandpass Filter
As shown in Figure (C), it consists of a series-resonant circuit shunted by an output resistance R0. It would be seen that this filter circuit can be produced by ‘swapping’ as series resonant bandstop filter. At f0, the series resonant impedance is very small and equal RL which is negligible as compared to R0. Hence, output voltage is maximum at f0 and falls to 70.7% at cutoff frequency f1 and f2 and shown in the response curve of Figure (D). The phase angle is positive for frequencies above f0 and negative for frequencies below f0 as shown in Figure (C) by the solid curve.
Following relationships hold good for this filter circuit.
AdBlock-2
Parallel-Resonant Bandpass Filter
It can be obtained by transposing the circuit elements of a bandstop a parallel-resonant filter. As shown in Figure (F), the output is taken across the two-branch parallel-resonant circuit. Since this circuit offers maximum impedance at resonance, this filter produces maximum output voltage V0 at f0. The amplitude-response curve of this filter is similar to that of the series-resonant bandpass filter discussed above [Figure (D)]. The dotted curve in Figure (E) represents the phase relationship between the input and output voltages of this filter. The following relationships apply to this filter :
Read article – Low-pass RC filter
Visit NCERTplanet.com for NCERT solutions and Textbook downloads
