KHN-equivalent voltage-mode filters using universal voltage conveyors Jaroslav Koton à , Norbert Herencsa ´ r, Kamil Vrba Brno University of Technology, Department of Telecommunications, Purkynova 118, 612 00 Brno, Czech Republic article info Article history: Received 24 August 2009 Accepted 11 February 2010 Keywords: Analog signal processing Frequency filter KHN-equivalent Voltage-mode Universal voltage conveyor abstract The analog circuit design is very often focused on the design of frequency filters employing different types of active elements. In this paper we present the universal voltage conveyor that is used for the design of the KHN-equivalent filters working in the voltage-mode. Auxiliary voltage inputs of the active elements are used to reduce the number of floating admittances in the structure. Both proposed structures are easily cascadable since the input and output impedances are in theory infinitely high and zero, respectively. The behavior of the filters has been verified through PSpice simulations and furthermore by experimental measurements. & 2010 Elsevier GmbH. All rights reserved. 1. Introduction High-input and low-output impedance second-order active filters are of great interest because several cells of this kind can be directly connected in cascade to implement higher order filters [1]. Another trend is the design of filters simultaneously realizing transfer functions that can be used in areas such as FM stereo demodulator, touch-tone telephone tone decoder, or three-way high-fidelity loudspeaker [2]. One of the best known multifunction filtering structures is the KHN (Kerwin–Huelsman–Newcomb) that enables mutually independent control of the quality factor Q and characteristic frequency o 0 [3]. The ever-present research and progress in microelectronics bring new or improved active elements suitable for the design of biquads. The current feedback amplifier (CFA) [4], operational transconductance amplifier (OTA) [5], current (CF) [6,7] and voltage followers (VF) [8,9], current conveyor (CC) [10,11], current follower transconductance amplifier (CFTA) [12], programmable current amplifier (PCA) [13], current differencing buffered ampli- fier (CDBA) [14], differential-input buffered and transconductance amplifier (DBTA) [15], current differencing transconductance amplifier (CDTA) [16], can be listed as examples. A number of voltage-mode multifunction filters can be found in the literature [17–23]. The topologies are of the TISO (three-input single output) or SITO (single-input three output) type and mutually independent control of the quality factor Q and characteristic frequency o 0 is not efficient since always two passive elements have to be changed (Q via one capacitor and one resistor, o 0 via two resistors or two capacitors). The voltage-mode SITO structures those behavior is equivalent to the KHN biquad are discussed in [24–30]. In these structures current conveyors [24–28] and transadmittance amplifiers [24], current feedback amplifiers [29], or current differencing buffered amplifier [30] are used. A number of solutions working in the current-mode can be found in [26,31–34]. This paper deals with the design of the voltage-mode KHN-equivalent filter employing universal voltage conveyors (UVC) [13,35–37]. Two structures using three active and seven passive elements are presented. The independent control of the quality factor Q and characteristic frequency o 0 is done only via one and two resistors. Using the auxiliary voltage input of the active element it is possible to reduce the number of floating admittances. Compared to [17–30] the input impedance is generally infinitely high and using three active elements the voltage responses are at ideally zero impedance. Hence, both structures are easily cascadable. The properties of the proposed filters have been verified by simulations and furthermore by experimental measurements. 2. Universal voltage conveyor The voltage conveyor (VC) has been presented in [38,39] as a dual to the current conveyor. Possible internal realization using bipolar and unipolar transistors was discussed in [40,41]. Based on the idea of the universal active element [42] and the experience with the universal current conveyor (UCC) [11,43–45] the universal voltage conveyor has been designed [13,35–37] and produced under the designation UVC-N1C. The universal voltage conveyor (Fig. 1) is six-port active element and the relationship Contents lists available at ScienceDirect journal homepage: www.elsevier.de/aeue Int. J. Electron. Commun. (AEU ¨ ) 1434-8411/$ - see front matter & 2010 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2010.02.005 à Corresponding author. Tel.: + 420 541 149 190; fax: + 420 541 149 192. E-mail addresses: koton@feec.vutbr.cz (J. Koton), herencsn@feec.vutbr.cz (N. Herencsa ´ r), vrbak@feec.vutbr.cz (K. Vrba). Int. J. Electron. Commun. (AEU ¨ ) 65 (2011) 154–160