, Volume 50, Issue 1, pp 59-67

Linearity of bulk-controlled inverter ring VCO in weak and strong inversion

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In this paper linearity of frequency modulation in voltage controlled inverter ring oscillators for non feedback sigma delta converter applications is studied. The linearity is studied through theoretical models of the oscillator operating at supply voltages above and below the threshold voltage of a transistor, bringing the transistors in respectively strong and weak inversion. The theoretical results are tested with more advanced models through spectreRF simulations. A soft rail approach implemented to improve linearity in weak inversion is proposed and demonstrated. The influence from voltage noise, process variations and temperature variations have also been simulated to indicate the advantages of having the soft rail bias transistor in the VCO.

Ulrik Wismar was born in Lunde, Denmark in 1978. He received M.Sc. in electrical engineering from The Technical University of Denmark, Kgs. Lyngby, Denmark in 2003. He is currently working towards a Ph.D. degree at the center for physical electronics, Ørsted·DTU at The Technical University of Denmark. His research interests is integrated analog baseband electronics with main focus on low power ADC circuits.
Dag T. Wisland received the M.Sc. and Dr. Scient degrees in electrical engineering from the Department of Informatics, University of Oslo, Norway in 1996 and 2003 respectively. From 1996 to 1998 he was a research fellow at Department of Informatics, University of Oslo. From 1998 to 2003 he was Head Engineer of the Microelectronics Systems group with the same department.
Dr. Wisland is currently Associate Professor at the University of Oslo and is serving as Head of the Microelectronic Systems research group at the Department of Informatics. His present research interests include analog/mixed-signal CMOS design, Ultra Wideband radio (UWB), and design of DAC/ADC with a particular focus on Delta-Sigma data converters for sensor and Microsystems applications. Dr. Wisland is a Member of IEEE.
Pietro Andreani received the M.S.E.E. from the University of Pisa, Italy, in 1988. He was at the Dept. of Applied Electronics (now Dept. of Electroscience), Lund University, Sweden, between 1990 and 1993, and again between 1995 and 2001 as an Associate Professor, when he was responsible for the analog IC courses, and where he received the Ph.D. degree in 1999. Since 2001 he has been a Professor at the Center for Physical Electronics, Ørsted·DTU, Technical University of Denmark, Kgs. Lyngby, Denmark, with analog/RF IC design as main research field.