Dual-Mode Tunable First-Order Universal Filters with Single VDGA

This article explores two compact structures to implement dual-mode first-order universal filters, providing lowpass, highpass, and allpass responses from the same structure. Both circuits offer savings in active components as they employ a single voltage differencing gain amplifier (VDGA). The first proposed filter has voltage inputs and current/voltage outputs with a single capacitor, which can perform three distinct filter functions in both voltage mode (VM) and trans-admittance mode (TAM). The latter filter, with current inputs and current/voltage outputs, consists of one capacitor and one resistor, which is capable of operating in both current mode (CM) and trans-impedance mode (TIM). Both of the proposed filters also offer an electronic adjustment of the passband gain and pole frequency through the VDGA’s transconductance values. The non-ideal implications of the VDGA on the first-order filters' performance are thoroughly examined. Computer simulations and experimental testing measurements validate the theoretical analyses.