Discuss about band pass filters (BPF).
Wednesday, 22 February 2012
High-Pass Filters
- Figure shows some common implementations of high-pass filters.
- Note that in each of the high-pass filters shown above, the inductors are in shunt with the input while the capacitors are in series with the input.
- This is because the reactance XL of an inductor increases with the signal frequency, i.e., XL = 2πfL, while the reactance XC of a capacitor decreases with the signal frequency, i.e., XC = 1 / 2πfC.
- Thus in these high-pass filters, the capacitors resist the passing of an ac signal as the frequency decreases, while the inductors shunt them towards the ground as the frequency decreases.
- Either way, the effect is to attenuate the signal as frequency decreases.
The following equations apply to the high-pass filters in Figure above:
1) L = Zo / 4πf
2) C = 1 / (4πf Zo)
3) Zo = sqrt(L/C)
4) f = 1 / (4π sqrt(LC))
where Zo is the line impedance and f is the cut-off frequency of the filter.
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