F3db Bandwidth of 2 Cascaded Independent Single-Pole Filters

Sept 02, 2012

The graph below shows the f3db bandwidth, relative to the lower-frequency filter, of two cascaded independent single-pole low pass filters (e.g. RC filters) as a function of the ratio f2/f1 of the f3db bandwidths of the filters. f2 is the higher filter frequency. For example, the f3db cutoff frequency of the higher-filter must be at least 4X higher than that of the lower filter for the net f3db bandwidth to be no less than 95% of the lower frequency filter: