A Novel Third-Order Leap-Frog Active Filter

Abstract

This paper presents the realization of third-order low-pass active-RC filters using a new Leap-Frog (LF) topology. New structure is a simplified LF structure with the elements calculated directly from the transfer function coefficients. Several versions of the circuits are presented and compared. The comparison to other common third-order filter sections is done, as well. The new LF filter has the reduced number of components, reduced complexity and straightforward design procedure compared to classical filters. As an illustration of the efficiency of the proposed new LF filter, the sensitivity analysis using Schoeffler sensitivity measure as well as output thermal noise analysis was performed on examples with Butterworth and Chebyshev 0.5dB pass-band ripple transfer functions. Using PSpice with a TL081 opamp model, the filter performance is simulated and the results compared and verified by measurements on a discrete-component breadboard filter. All equations needed for the step-by-step design are given.

U radu je predstavljena realizacija nisko-propusnog aktivnog-RC filtra trećeg reda koji upotrebljava novu “leap-frog” (LF) topologiju. Nova struktura je pojednostavljena LF struktura s elementima koji se računaju direktno iz koeficijenata prijenosne funkcije. Nekoliko inačica krugova je prikazano i obavljena je usporedba. Napravljena je usporedba također i s drugim uobičajenim filtarskim sekcijama trećeg reda. Novi LF filtar ima smanjeni broj komponenata, smanjenu kompleksnost i jednostavniji postupak projektiranja u usporedbi s klasičnim filtrima. Za ilustraciju učinkovitosti predstavljenog novog LF filtra, provedena je analiza osjetljivosti pomoću Schoefflerove mjere osjetljivosti i analiza termičkog šuma na izlazu na primjerima s prijenosnim funkcijama po Butterworthu i Chebyshevu s valovitošću u području propuštanja od 0.5 dB. Pomoću PSpice-a s modelom pojačala TL081, filtarska svojstva su simulirana, uspoređena i potvrđena mjerenjima na filtrima realiziranim pomoću diskretnih elemenata na štampanoj pločici. U radu su dane sve potrebne jednadžbe u postupku projektiranja korak po korak.

Key words:

• Leap-Frog filters
• Third-Order filter sections
• Low-Sensitivity and low-noise filters
• Active-RC filters

Ključne riječi:

• leap-frog filtri
• filtarske sekcije trećeg reda
• niskoosjetljivi i niskošumni filtri
• aktivni RC filtri

Additional information

Notes on contributors

Neven Mijat

Neven Mijat received his B.Sc., M.Sc. and Ph.D. degrees in Electrical Engineering from the Faculty of Electrical Engineering, University of Zagreb in 1970, 1974 and 1984, respectively. In 1970 he joined the Department of Electronic Systems and Information Processing at the Faculty of Electrical Engineering, University of Zagreb, where he is currently professor within the Networks, Systems and Signals group. At the Faculty he is involved in teaching lectures in undergraduate courses involving Network Theory, Filters, Analogue circuits, SC circuits, and in the postgraduate courses ‘Filter design’, and ‘Numerical methods in system design’. His current research interests include data acquisition systems and filter theory and realization methods. He was also leading a number of R&D projects. He is member of IEEE, CROMBES, KoREMA and some other professional societies. He was a principal investigator for few scientific projects and development projects for companies. He received the ‘Josip Loncar’ silver plaques for his M.Sc. and Ph.D. theses in 1974 and 1984 respectively.

Dražen Jurišić

Dražen Jurišić is associate professor of the Faculty of Electrical Engineering at the University of Zagreb in Croatia where he received his B.Sc., M.Sc. and Ph.D. degrees in Electrical Engineering in 1990, 1995 and 2002, respectively. In 2005 he was elected as assistant professor and in 2011 as associate professor. He is involved in teaching lectures in undergraduate course on ‘Electrical circuits’, and in graduate course on ‘Analog and mixed signal processing’. Present interests include analog and digital signal processing and filter design. From 1997 until 1999 he was with Swiss Federal Institute of Technology (ETH) Zürich, Switzerland, as holder of Swiss Federal Scholarship for Foreign Students doing Ph.D. research in the field of analog active-RC filters. He was rewarded with the silver plaque ‘Josip Loncar’ for his Ph.D. thesis. Since November 2008 he is visiting Bar-Ilan University, Israel and till now he spent 12 months there as a researcher. He is a member of KoREMA and IEEE-CAS society. He speaks English and German.

George S. Moschytz

George S. Moschytz is Dean of the Faculty of Engineering at the Bar-Ilan University in Israel. Present interests include analog and digital, sampled-data, and adaptive filters, for communication systems. Earlier Professor Moschytz was with RCA Labs in Zürich, Bell Telephone Labs, Holmdel, NJ, where he supervised a group designing analog and digital integrated circuits for data communications, and at ETH, Zürich, as Professor and Director of the Institute for Signal and Information Processing. Author of ‘Linear Integrated Networks: Fundamentals’ and ‘Linear Integrated Networks: Design’, and co-author of the ‘Active Filter Design Handbook’, and ‘Adaptive Filter’ (in German). Editor of ‘MOS Switched-Capacitor Filters: Analysis and Design’, and co-editor of ‘Tradeoffs in Analog Design’. Authored many papers in the field of network theory, design, and analysis, and holds numerous patents in these areas. Professor Moschytz has held the position of president of the IEEE Circuit and Systems Society, and is an elected member of the Swiss Academy of Engineering Sciences. He is a Life-Fellow of the IEEE, and has received several IEEE awards, including the IEEE CAS Education Award.