Capacitorless digitally programmable fractional-order filters

Novel topologies of fractional-order filters, implemented using the internal gate-source capacitance of MOS transistors, are introduced in this paper. This has been achieved using current-mirrors as active elements, resulting into resistorless realizations due to the employment of the small-signal transconductance parameter of the MOS transistor. This also offers the capability for electronic tuning of the frequency characteristics of the derived filter structures. The evaluation of the proposed technique has been performed through the design of a generalized fractional-order filter, which is also digitally programmed in such way that the four standard filter functions are offered. The behavior of the filter has been evaluated using the Cadence IC design suite and the Design Kit provided by the Austrian Micro Systems 0.35 μm CMOS process.