OTA-C filter design using inductor substitution and Bruton transformation methods

Operational transconductance amplifier-capacitor (OTA-C) filters are normally designed by simulating low sensitivity LC filters. The evaluation of parasitic effects on OTA-C filters for the inductor substitution method is usually by direct circuit analysis, which is too complex for high order filters. The practical performance of the Bruton transformation method in OTA-C filter design has not previously been investigated. The author presents a method for evaluating the parasitic effect in OTA-C filters based on the inductor substitution method, which uses very simple formulas for the magnitude and phase sensitivities of the passive LC ladder and the equivalent loss resistance and the change in the equivalent inductance of each OTA-C inductor due to nonidealities in its constituent OTAs. The Bruton transformation method is discussed and demonstrated not to be attractive for OTA-C filter design due to the large component numbers and parasitic effects