Bipolar State-Variable Filter for High Frequencies

A time-continuous programmable State-Variable filter is presented that has been realised using bipolar OTA´s. A high input resistance and a good linearity is maintained irrespective of the programming of the transconductance using an OTA with a separated voltage-to-current input stage and a current-attenuation stage. A special common-mode loop is implemented to avoid the charging of the filter capacitors by an output bias current. Filters can be designed with resonance frequencies up to 40 MHz and Q factors ranging from 1 to 10.