New Voltage and Current Mode First-order All-pass Filters Using Single FTFN

In this study, a voltage-mode and a current-mode first-order all-pass filter are presented. The voltage-mode allpass filter contains a single FTFN, a capacitor and two grounded resistors. The all-pass filter uses less passive elements than the other all-pass filters in the literature. The current-mode filter also uses a single FTFN, a capacitor and three resistors. The output of the current-mode all-pass filter exhibits high output impedance so that this property makes the circuit very attractive from the viewpoint of cascadability. The tracking error performance for the proposed filters is also examined. The theoretical results are verified by PSPICE simulations. Übersicht In dieser Arbeit werden jeweils ein Allpaßfilter erster Ordnung vom Spannungstyp bzw vom Stromtyp vorgestellt. Ersteres enthält neben einem FTFN einen Kondensator und zwei einseitig geerdete Widerstände und somit weniger passive Elemente als aus der Literatur bekannt Das Filter vom Stromtyp verwendet neben dem einen FTFN einen Kondensator und drei Widerstände. Sein Ausgang hat eine hohe Ausgangsimpedanz, eine Eigenschaft, die diesen Schaltkreis für kaskadierte Funktionen interessant werden läßt. Eine Untersuchung der Gleichlauffehler wird vorgenommen. Die theoretischen Ergebnisse werden mit PSPICE-Simulationen bestätigt. Für die Dokumentation FTFN / Allpaßfilter / Schaltkreise vom Stromund Spannungstyp Frequenz 54(2000) 7-8 l. Introduction 2. The proposed circuits First-order all-pass filters are widely used for phase shifting while keeping the amplitude of input signal constant over the frequency range of interest The all-pass filters can be also utilised for synthesis of multiphase oscillators and second-order band-pass filters 11 ]. Op-amp and CCII-based first-order all-pass filters are available in the literature [1-3]. However the four terminal floating nullor (FTFN) has been also receiving considerable attention recently, since it has been shown that an FTFN is a very flexible and versatile building block in active network synthesis [4-14]. The FTFN contains both floating voltage follower and current follower without having any common node which makes easy synthesis of current and voltage-mode analogue signal processing circuits. In [1] a voltage mode all-pass filter has been presented which contains an op-amp, three resistors and a capacitor. A set of CCII+ based allpass filters have been presented in the literature [3]. The circuits use more than one floating elements which is not suitable 1C integration principles. On the contrary a few current-mode first order all-pass filters have been proposed up to now [5]. The filter employs a single FTFN, a capacitor and two resistors. The main disadvantage of this circuit is that it can not provide high impedance current output. An additional current buffer is needed to sense the output current. In this study a voltage-mode and a current-mode first-order all-pass filters are presented. The voltage-mode all-pass filter contains a single FTFN, a capacitor and two grounded resistors. It uses less passive elements than the other filters in the literature [ 1-3]. The current-mode filter also uses a single FTFN, a ca-, pacitor and three resistors. The output of the current-mode filter exhibits high output impedance so that this property makes the circuit very attractive from the viewpoint of cascadability. Both voltage and current mode all-pass filters can also use the CCIIinstead of the FTFN, since the FTFN is a more general active building block compared to a current conveyor and an operational amplifier. Tracking error analyses for the proposed filters are also performed. 1 Sakarya University, Esentepe, Adapazan, Turkey 2 BogaziQi University, Bebek, Istanbul, Turkey 3 Istanbul Technical University, Maslak, Istanbul, Turkey A FTFN is equivalent to an ideal nullor or is called operational floating amplifier [4-14]. The FTFN shown in Fig. 1 is characteris-ed by the following port relations: