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Analogue Signal
Processing |
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THE
FILTERING PROCESS |
Consider an ideal band-pass filter
(BPF) whose transfer is shown in the illustration below.
The filter passes without distort0ion all frequencies
between its lower cutoff frequency fL
and its upper cutoff frequency fU.
The frequency range ( fU - fL)
is called the pass-band; the filter has
zero response outside its pass-band. |
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Characterstics of an ideal
band-pass filter |
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Its transfer function can be written
as  |
| Where K is the voltage
gain and t 0 is the time delay of the filter. |
An ideal low-pass filter (LPF) has fL
= 0, B= fH . An ideal high-pass
filter (HPF) has .
Ideal low-pass and band-pass filters are sometimes called
zonal filters, the zone being their
finite pass-band. |
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Characterstics
of (a) ideal low-pass filter, (b) ideal high-pass filter.
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Ideal low-pass filters are our main
concern. We write its transfer function as: |
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Note that B
has two meanings; bandwidth and upper cutoff frequency.
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