Disclosed is a filter circuit assembly that includes a filter stage with a variable resistor and a resistor/capacitor (RC) oscillator. A controlling output of the RC oscillator controls the value of the variable resistor. The RC oscillator itself also includes a variable resistor. The controlling output...http://www.google.es/patents/US7212068?utm_source=gb-gplus-sharePatente US7212068 - Tunable Sallen-Key filter stage and filter assembly
Tunable Sallen-Key filter stage and filter assembly
