An Approach to CFOA-based Second-Order Universal Filters

In this work, two universal current-mode (CM) filters are proposed. These filters are single-input three-output filter and three-input single-output filter. The proposed single-input CM filter simultaneously provides low-pass filter (LPF), high-pass filter (HPF), and band-pass filter (BPF) responses without requiring passive component matching. The LPF and BPF provide gains. Additionally, a notch filter (NF) response can be obtained by subtracting the output current of the LPF from the output current of the HPF, while an all-pass filter (APF) response can be achieved by subtracting the output current of the BPF from the output current of the NF. The proposed three-input CM filter generates LPF, HPF, BPF, NF, and APF responses at its output when the inputs are appropriately selected. The BPF response of the three-input CM filter has a gain. However, HPF, NF, and APF responses require a passive component matching condition. Both proposed circuits contain two grounded capacitors, which makes them suitable for integrated circuit technology and exhibit low active and passive sensitivities. The performance of the proposed filters is verified through SPICE simulations using 0.18 µm Taiwan Semiconductor Manufacturing Company (TSMC) complementary metal-oxide-semiconductor (CMOS) technology parameters. Additionally, experimental validation is performed using AD844s to demonstrate their practical performance.