On the Realization of MOS-Only Allpass Filters
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On the Realization of MOS-Only Allpass Filters Hacer A. Yildiz · Serdar Ozoguz · Ali Toker · Oguzhan Cicekoglu
Received: 7 May 2012 / Revised: 13 September 2012 / Published online: 4 October 2012 © Springer Science+Business Media New York 2012
Abstract The objective of this paper is to present a simple filter topology, which can be used to implement first- and second-order MOS-only allpass filters. The resulting filters realize the allpass functions without using any external passive components; hence these occupy very small chip area and are capable of operating at high frequencies. Cadence Spectre simulation and experimental results verifying the main advantages of the filters are provided. Keywords Analog filters · Integrated circuits · Allpass filters · Active-only filters
1 Introduction In the last decade, significant efforts have been devoted to the study and design of MOS transistor-only active circuits (or MOS-only circuits); i.e. circuits that do not employ any external passive components, resistive or reactive (i.e. capacitors or inductors), but rather that exploit the intrinsic capacitors within the transistors [7, 8, 10, 13, 16, 25, 26, 28]. These circuits provide very useful advantages from IC realization H.A. Yildiz () · S. Ozoguz · A. Toker Faculty of Electrical-Electronics Engineering, Istanbul Technical University, Maslak, Instanbul 34469, Turkey e-mail: [email protected] S. Ozoguz e-mail: [email protected] A. Toker e-mail: [email protected] O. Cicekoglu Faculty of Electrical-Electronics Engineering, Bogazici University, Bebek, Instanbul 34342, Turkey e-mail: [email protected]
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Circuits Syst Signal Process (2013) 32:1455–1465
viewpoint such as: (i) low occupied chip area as a result of not using any intentional, external capacitors, (ii) capability of operating at high frequencies as most significant parasitic capacitances are taken into account during the synthesis procedure, (iii) electronic tuning property of the important filter parameters, since the design of these circuits relies on the device transconductances which can be controlled by bias currents. On the other hand, allpass filters are very useful blocks for realizing phase shifters, phase equalizers [18], high-Q bandpass filters [3, 24], quadratic oscillators with improved frequency stability [29] and even for implementing arbitrary magnitude filters designed with classical approximations such as Butterworth, Chebyshev and Elliptic characteristics [5]. While many active RC allpass filters are proposed in the literature [1, 2, 6, 9, 11, 12, 14, 15, 20–23, 27], to the best of the authors’ knowledge, only one single MOS-only allpass filter realization exists in the literature [13]. However, this circuit realizes only first-order transfer functions, thus lacks the possibility to realize complex poles and zeros. In this paper, we propose a simple filter topology that can be used to implement both first- and second-order MOS-only allpass filters. The filters derived from this topology provide all the advantages mentioned ab
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