Syntiac pages - OB-VCF Module

Syntiac pages - OB-VCF Module

This filter is basically a dual RC filter with feedback, where the R's are replaced with OTAs. Changing the control current on the OTAs shifts the cutoff frequency of the two lowpass filters. Creating HighPass and BandPass by use of two lowpass filters is simply basic arithmatic in the frequency domain. Where HiPass=Input-LowPass and BandPass=Input-(LowPass+HighPass). The resistors scale all voltages to the correct levels. The feedback path creates a resonance peak around the cutoff frequency.