Out in Front: September 12, 1996

A complete eighth-order, elliptic, lowpass filter supports cutoff frequencies adjustable to as high as 12 kHz. The LTC1069-1 from Linear Technology, in an SO-8 package or eight-lead DIP, requires only external supply bypass capacitors. It provides 72 to 80 dB of dynamic range and operates from supplies from one 3.3V source up to ±5V; the supply voltage determines the maximum achievable operating frequency.

You set the cutoff frequency via an external clock running at 100 times the desired cutoff value. Passband ripple is typically ±0.15 dB. Stopband attenuation factors are 20, 52, and 70 dB at 1.2, 1.4, and two times the cutoff frequency, respectively. Wideband noise--an important factor in filters--is 120 µV rms. Supply current for this $4.70 (1000) IC ranges from 2 to 3.8 mA, depending on supply voltage.

—by Bill Schweber

Linear Technology Corp, Milpitas, CA. (408) 432-1900, fax (408) 434-0507.