Electronically Tunable Frequency Filters Based on Transformation Cells

In the paper a novel circuit structure realizing a grounded parallel nth-order synthetic immittance system is introduced. Voltage conveyors (VCs) and transadmittance amplifiers (OTAs) are used as active elements. The use of the current-controlled OTAs enables modifying simply the parameters of the synthetic element designed. A further advantage of the synthetic element presented is that all the passive elements used are grounded. The application of the controlled synthetic elements is shown on a realization of tunable 4th-order frequency filters, where the cut-off frequency can be changed in a range from 1 kHz to 1 MHz. The symbolic- analysis conclusions are supplemented by PSpice simulation results.