LMF90

·Center frequency set by external clock or on-board clock oscillator
·No external components needed to set response characteristics
·Notch width, attenuation, and clock-to-center-frequency ratio independently programmable
·14 pin 0.3× wide package

The LMF90 is a fourth-order elliptic notch (band-reject) filter based on switched-capacitor techniques. No external components are needed to define the response function.

The depth of the notch is set using a two-level logic input, and the width is programmed using a three-level logic input. Two different notch depths and three different ratios of notch width to center frequency may be programmed by connecting these pins to Va, ground, or Vb. Another three-level logic pin sets the ratio of clock frequency to notch frequency. An internal crystal oscillator is provided. Used in conjunction with a low-cost color TV crystal and the internal clock frequency divider, a notch filter can be built with center frequency at 50 Hz, 60 Hz, 100 Hz, 120 Hz, 150 Hz, or 180 Hz for rejection of power line interference. Several LMF90s can be operated from a single crystal. An additional input is provided for an externally-generated clock signal.