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Low-Pass Filter A low-pass filter is a filter that passes low frequencies well, but attenuates (reduces) higher frequencies. The so-called cutoff frequency divides the range of frequencies that are passed and the range of frequencies that are stopped. In other words, the frequency components higher than the cutoff frequency will be stopped by a low-pass filter. The actual amount of attenuation for each frequency varies by filter design. An Inductive low-pass filter inserts an inductor in series with the load, where a capacitive low-pass filter inserts a resistor in series and a capacitor in parallel with the load. The former filter design tries to “block" the unwanted frequency signal while the latter tries to short it out. Figure 10-220 illustrates this type of circuit and the frequency/current flow response.
High-Pass Filter A high-pass filter (HPF) is a filter that passes high frequencies well, but attenuates (reduces) frequencies lower than the cutoff frequency. The actual amount of attenuation for each frequency varies once again depending on filter design. In some cases it is called a low-cut filter. A high-pass filter is essentially the opposite of a low-pass filter. It is useful as a filter to block any unwanted low frequency components of a signal while passing the desired higher frequencies. Figure 10-221 illustrates this type of circuit and the frequency/current flow response.
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