CFOA‐based simple mixed‐mode first‐order universal filter configurations

• Published in: International journal of circuit theory and applications 2022-07, Vol.50 (7), p.2631-2641
• Main Authors: Bhaskar, Data Ram, Raj, Ajishek, Senani, Raj, Kumar, Pragati
• Format: Article
• Language: English
• Subjects: all pass filters; Amplification; CFOA; Circuits; Configurations; current mode; Electric potential; first‐order filters; high pass filters; Input impedance; low pass filters; Topology; transadmittance mode; transimpedance mode; universal filters; Voltage; voltage mode; Workability
• ISSN: 0098-9886; 1097-007X
• DOI: 10.1002/cta.3289

This brief communication presents two current feedback op‐amp (CFOA)‐based simple first‐order mixed‐mode universal filter topologies—one of them providing first‐order low‐pass (LP), high pass (HP), and all pass (AP)—all the three filters in voltage‐mode (VM)/trans‐admittance‐mode (TAM) while the other one realizing the quoted three functions in current‐mode (CM)/trans‐impedance‐mode (TIM). Except the all pass filter realization from the first configuration which needs a second CFOA also as gain‐of‐two amplifier, in all the remaining cases of both the configurations, only a single CFOA is needed. The other notable features of the circuits are employment of only three resistors and a grounded capacitor (as preferred for IC implementation) and the availability of independent tunability of the gain (H0) and cut‐off frequency/pole frequency (ω0) of all the three filters, in both the cases. In spite of not offering ideally infinite input impedance in VM/TAM mode and ideally zero input impedance in CM/TIM mode, the circuits still possess easy cascadability due to providing a voltage output from a low‐output impedance terminal W while the current output from the high output impedance terminal Z. Non‐ideal and sensitivity analyses have also been carried out. The workability of the proposed circuits has been demonstrated through PSPICE simulations and experimental results using the commercially available AD844‐type IC CFOA. This paper presents two new first‐order universal active filter configurations employing a single current feedback operational amplifier, three resistors and a grounded capacitor, as preferred for IC implementation. Both the proposed circuits realize low pass, high pass and all pass filters; the first one in voltage mode and trans‐admittance mode and the second one in current mode and trans‐impedance mode. Both circuits facilitate independent tunability of the gain and the cut‐off frequency/pole frequency in case of all the three filters.