LMF380

LMF380 Triple One-Third Octave Switched-Capacitor Active Filter November 1995 LMF380 Triple One-Third Octave Switched-Capacitor Active Filter General Description The LMF380 is a triple one-third octave filter set designed for use in audio audiological and acoustical test and measurement applications Built using advanced switched-capacitor techniques the LMF380 contains three filters each having a bandwidth equal to one-third of an octave in frequency By combining several LMF380s each covering a frequency range of one octave a filter set can be implemented that encompasses the entire audio frequency range while using only a small fraction of the number of components and circuit board area that would be required if a conventional active filter approach were used The center frequency range is not limited to the audio band however Center frequencies as low as 0 125 Hz or as high as 25 kHz are attainable with the LMF380 The center frequency of each filter is determined by the clock frequency The clock signal can be supplied by an external source or it can be generated by the internal oscillator using an external crystal and two capacitors Since the LMF380 has an internal clock frequency divider ( d 2) and an output pin for the half-frequency clock signal a single clock oscillator for the top-octave LMF380 becomes the master clock for the entire array of filters in a multiple LMF380 application Accuracy is enhanced by close matching of the internal components the ratio of the clo...