Low-Noise Active-RC Allpole Filters Using Optimized Biquads

Abstract

In this paper it is shown that active-RC filters can be designed to have low-sensitivity to passive components and at the same time possess low output thermal noise. The design procedure of low-noise and low-sensitivity, positive-feedback, second- and third-order low-pass allpole filters, using impedance tapering, has already been published. The noise analysis in this paper was extended to the high-pass and band-pass filters and those with negative-feedback. The optimum designs, regarding both noise and sensitivity of most useful filter sections were summarized in the table form (as a cookbook) and demonstrated on examples. The classical methods were used to determine output noise spectral density and total rms output noise of filters. It was found that low-sensitivity filters with minimum noise have reduced resistance levels, low Q-factors, low-noise operational amplifiers and use impedance tapering design.

U ovom radu je prikazano da optimalne aktivne RC filtarske sekcije s niskim osjetljivostima na varijacije pasivnih komponenata istovremeno imaju nizak nivo termičkog šuma na izlazu. Postupak projektiranja nisko osjetljivih i nisko šumnih, nisko-propusnih filtarskih sekcija drugog i trećeg reda s pozitivnom povratnom vezom pomocu ‘skaliranja impedancija’ je već objavljen. U ovom radu je analiza izlaznog šuma proširena na nove sekcije koje realiziraju pojasno-propusnu i visoko-propusnu frekvencijsku karakteristiku kao i na sekcije koje koriste negativnu povratnu vezu u realizaciji. Svi postupci optimalnog projektiranja u smislu niskog šuma i niske osjetljivosti za najreprezentativnije filtarske sekcije su sažeti i raspoloživi u obliku tablica s postupkom projektiranja ‘korak po korak’ (kuharica) te pokazani na primjerima. U istraživanju su korištene klasične metode za određivanje spektralne gustoće šuma i totalne efektivne vrijednosti šuma na izlazu filtara. Pokazano je da filtri sa niskim osjetljivostima koji istovremeno imaju nizak nivo šuma posjeduju niske vrijednosti otpora, realiziraju niske Q faktore, koriste niskošumna operacijska pojačala u realizaciji te su projektirana metodom skaliranja impedancija.

Key words:

• Low sensitivity
• Low noise
• Low-
• High-
• Band-pass active-RC filters
• Single-amplifier biquads
• Allpole filters

Ključne riječi:

• niska osjetljivost
• niski šum
• nisko-
• visoko- i pojasno-propusni aktivni RC filtri
• bikvadratne sekcije s jednim pojačalom
• svepolni filtri

Additional information

Notes on contributors

Dražen Jurišić

Dražen Jurišić is assistant 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. He is involved in teaching lectures in undergraduate I courses on “Electrical circuits”, “Signals and sysI tems” and “Analog and mixed signal processing I circuitry”. Present interests include analog and digital signal processing and filter design. He worked as a researcher on the three scientific projects supported by Ministry of Science and Technology, Republic of Croatia. 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. He is a member of KoREMA and IEEE-CAS society. He speaks English and German.

George S. Moschytz

George S. Moschytz is head of the Electrical and Computer Engineering Department 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.

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.