AC2 Fundamentals Unit 5 – Low- and High-Pass Filters
UNIT 5 – LOW- AND HIGH-PASS FILTERS
UNIT OBJECTIVE
At the completion of this unit, you will be able to determine the cutoff frequencies and
attenuations of RC and RL low- and high-pass filters by using test circuits.
UNIT FUNDAMENTALS
A filter is a frequency-selective circuit that permits signals of certain frequencies to pass while it
rejects signals at other frequencies.
A low-pass filter, as its name implies, passes low frequencies but rejects high frequencies.
The dividing line between the passing of low frequencies and the rejecting of high frequencies is
the cutoff frequency (fc), or -3 dB point. In a low-pass filter, signals lower than the cutoff
frequency pass essentially unmodified. Frequencies higher than the cutoff frequency are greatly
attenuated, or reduced.
In a high-pass filter, signals higher than the cutoff frequency pass essentially unmodified. Signals
lower than the cutoff frequency are greatly attenuated, or reduced.