GYRATOR FILTERS BASED ON OPERATIONAL AMPLIFIERS.

A gyrator is described based on two operational amplifiers realizing a grounding inductance. These are used to assemble bandpass filters for center frequencies of 30 and 150 Hz. The first filter is intended for extracting the fundamental from a meander-type signal with a temperature instability in the phase of the output signal of less than equivalent to 0. 5 degree over the range plus or minus 50 degree C. The suppression at 15 and 60 Hz is 17 and 23 db respectively. The bandpass filter for the 150 Hz is based on three tuned circuits with resonant frequencies of 147, 153, and 150 Hz, respectively, the Q of each circuit being 30-40, the suppression of signals at frequencies 120 and 180 Hz being more than 54 db, the temperature instability of the frequency response being less than equivalent to 5% over the range plus or minus 50 degree C.