TO-OTA based current-mode biquad filters Dattaguru V. Kamath Professor, Departmentof E&C Engg., Manipal Institute of Technology, Manipal University, Manipal, India Abstract—In this paper, a general two-admittance current-mode circuit structure using triple-output OTA is explored to derive new second-order multi-function filters using OTAs with few extra current outputs and with/ without grounded capacitors. Biquads filters have been realized by using various admittances like OTA-simulated resistor, series and parallel OTA-C resonators in the proposed general structure. PSPICE simulation results are also given for the proposed circuits. Index Terms—Active filters, DO-OTA, TO-OTA, OTA-C filters, OTA-C biquads, Current-mode circuits I. INTRODUCTION The OTA-C approach [1]-[9] is one of the most preferred design methods for continuous-time (CT) integrated filter design at high frequencies. The design of current-mode OTA-C filters employing active elements like Dual Output OTAs (DO-OTA) [2], [3], [4], Triple Output OTAs (TO-OTA) [5]-[6] and Multiple Output OTAs (MO-OTA) [7], [8] have been reported. The biquads are the basic building blocks for the realization of CT filters of higher order. In the literature, different circuit configurations for realization of current-mode biquads using OTA have been described i.e., a single DO-OTA and five admittance model [3], two-integrator loop structure [4], [7], [8] etc. The realization of current-mode OTA-C first-order and second- order filters using DO-OTA based general two-admittance circuit configuration [9] with two input currents has been discussed in the literature. In this paper, the proposed TO-OTA based general current-mode two-admittance circuit structure with only one input current is presented in Section II. In Section III, the proposed general basic topology is shown to be useful to realize various second-order filters by substituting various admittances in place of   and   . Biquads using only grounded capacitors and in some cases using floating capacitors also have been considered. The summary of the proposed biquads is discussed in Section IV. SPICE simulation results are presented in Section V to demonstrate their practical usefulness. The concluding remarks are given in Section VI. II. PROPOSED TO-OTA BASED TWO-ADMITTANCE CIRCUIT CONFIGURATION The circuit symbol of TO-OTA is shown in Fig.1. Note that   + =   − =      −     (1) Here, Io + , Io - are output source and sink currents respectively, Vi + andVi - denote non-inverting and inverting input voltages of the TO-OTA respectively. Figure1: Circuit symbol of TO-OTA In the general DO-OTA based two-admittance circuit configuration (Fig. 2 in) [9], we consider two input currents and only one feedback path (i.e., either (i) α = 1, β = 0 or (ii) β = 1, α = 0). The proposed TO-OTA based circuit configuration shown in Fig. 2 for realizing OTA-C biquads has been derived from the general two-admittance circuit configuration (Fig. 2 in [9]) by considering single input current and two feedback paths (i.e., α = 1, β = 1). The generalized current-input current-output (CICO) transfer function for this circuit can be shown to be     =         +     +    (2) - o V + + I V + + i + I o - m I o + i g - - Techscripts 15 Transactions on Engineering and Sciences ISSN: 2347-1964 (Online) 2347-1875 (Print) Vol.2, Issue 8, August 2014