Title:Log Domain Integrator using Quasi-Floating Gate MOSFET
VOLUME: 11 ISSUE: 2
Author(s):Harjeet Kaur, Rockey Gupta* and Susheel Sharma
Affiliation:Department of Electronics, Faculty of Science, University of Jammu, Jammu, Department of Electronics, Faculty of Science, University of Jammu, Jammu, Department of Electronics, Faculty of Science, University of Jammu, Jammu
Keywords:Compressor, expander, integrator, log domain, weak inversion, threshold voltage.
Abstract:Background: A MOS transistor operating in weak inversion exhibits logarithmic behavior and could
serve as replacement of bipolar transistors which have often been employed in implementing log domain
circuits. However, threshold voltage restricts the operation of MOS based log domain circuits at low supply
voltage which could be eliminated by floating gate transistors (FGMOS) at the cost of low gain, low output
impedance and degraded bandwidth. These limitations can be further overcome by using quasi-floating gate
MOSFET (QFGMOS).The log domain technique has been employed to enhance the dynamic range of analog
circuits suitable of operation at low supply voltage.
Methods: In this paper, we have designed QFGMOS based integrator and its performance has been compared
with CMOS and FGMOS versions. The behavior of these circuits has been verified by using OrCAD PSpice
with level 7 parameters for 0.13 µm technology obtained from TSMC with supply voltage of 1V.
Results: It has been observed that QFGMOS based compressor and expander exhibits better performance as
compared to their CMOS and FGMOS counterparts. Further QFGMOS based log domain integrator has been
designed and its performance compared with that of CMOS and FGMOS based log domain integrators and
found that QFGMOS based log domain integrator exhibits larger bandwidth (4.26 MHz) as compared to
FGMOS (3.2 MHz) and it dissipates less power (88.7 µW) then FGMOS (0.114 mW) and CMOS (0.129 mW)
based log domain integrators and could be useful for low voltage applications.
Conclusion: In this paper functional blocks of log domain integrator like compressor and expander have
been designed using CMOS, FGMOS, QFGMOS transistors and their performance studied through
PSpice simulations. It has been observed that QFGMOS based compressor and expander exhibits better
performance as compared to their CMOS and FGMOS counterparts. Further QFGMOS based log
domain integrator has been designed and its performance compared with that of CMOS and FGMOS
based log domain integrators.
