The National Semiconductor LMF90 integrated circuit contains all the elements for the elaboration of a 60 Hz crystal-controlled filter. Its central frequency is fixed by a crystal and can be between 0.1 and 30 kHz. The maximum guaranteed precision is 1.5% and there is the possibility to program the width of the rejection and attenuation band, among others. The supply can be made with simple or symmetrical sources, from 4 to 15 V. The attenuation is selected in the range of 39 to 48 dB (tip). The crystal for the indicated frequency is obtained from color televisions and is therefore easy to obtain.
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