The quasi- or pseudo-floating gate (QFG) technique addresses a key issue with the floating-gate MOS transistor technique,
by using ultra-high resistances to provide dc paths to otherwise floating nodes. Several ways have been suggested to implement
the quasi-infinite resistors (QIRs). In this paper, basic QIR structures are analyzed and compared, and three sources of error,
dc offset, signal distortion, and signal-dependent offset, are defined. Then, through simulations and experiments, the suitability
of several QIR implementations for use in various applications is compared. A particular QIR implementation is found to minimize
dc offset, but requires voltage swings to be limited to less than a diode turn-on voltage. Some application circuits using
quasi-floating gate are presented, including a QFG translinear geometric-mean circuit and QFG low-voltage fully-differential
amplifiers with QFG common-mode feedback using several QIR structures. Measurements on current-mode QFG circuits exhibit large
offsets and very long turn-on transients, which could limit practical application of this technique.
Key Words Analog - low-voltage - floaing-gate - ac-coupled
Inchang Seo received B.S. and M.S. degrees in physics from Hanyang University, Seoul, Korea, in 1988 and 1990. He also received M.S.
and Ph.D degrees in electrical and computer engineering from the University of Florida, Gainesville, Florida, in 2000 and
2004, respectively. During 1990–1997, he worked as a researcher at the Agency for Defence Development (ADD), Chinhae, Korea.
His responsibility was design, development, and evaluation of underwater acoustic transducers and sonar systems which were
based on piezoelectric, magnetostrictive, and fiber-optic transducers. His main research interests involve low-voltage, low-power,
high-precision analog and mixed-signal integrated circuit design including low-voltage wide-band DS data converters, precise
bias circuit blocks, low-power charge transfer amplifiers and filters, floating-gate CMOS analog circuits, and quasi-floating
gate analog applications.
Robert M. Fox received the B. S. degree in Physics from the University of Notre Dame in 1972, and M. S. and Ph. D. degrees in Electrical
Engineering from Auburn University in 1981 and 1986, respectively. Since 1986 he has been on the Electrical and Computer Engineering
faculty at the University of Florida, where he is an Associate Professor. Dr. Fox's research emphasizes circuit design and
modeling for advanced IC technologies. He has worked on a variety of topics, including analog circuit design, cryogenic electronics,
circuit design with SOI, radiation response of semiconductors, noise modeling, and modeling of transistor self-heating. Currently
his research interests center on design-oriented analysis of analog integrated circuits, including low-voltage circuit techniques,
design of log-domain circuits, analog test strategies and transistor modeling. Dr. Fox is a member of the Analog Signal Processing
Technical Committee of the Circuits and System Society, having served as Committee Chairman and ISCAS Track Chair. He is a
member of the Analog/Mixed-Signal Technical Committee for the IEEE Bipolar/BiCMOS Circuits and Technology Meeting (BCTM).