A low-power and low-Gm linear transconductor utilizing control of a threshold voltage

For medical devices, low frequency applications are required. Thus, a linear transconductor which has a very low transconductance is needed. A conventional low-power and low-transconductance transconductor operating in subthreshold region using the source-degeneration has a problem that the linear input range is limited because the drain-source resistance for the source-degeneration is changed by the input voltage. This paper proposes a linear transconductor that is realized by the scheme that the threshold voltages of the transistors are changed by the attenuated input voltage using body effect and reverse short-channel effect. The proposed transconductor is optimally designed using maximally flat approximation method and Newton-Raphson method. The characteristics of the proposed transconductor are confirmed by simulation. The 1 % linear input range, which is around 110 mV, is improved as compared with the conventional transconductor. The 1 % linear input range is defined as the maximum differential input voltage that the error of the transconductance is within 1 %. The power consumption is 881 nW for the transconductance Gm=1.05\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$G_m=1.05$$\end{document} μS when the input voltage is 0 V. The THD is around -60dB\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-60\, \hbox {dB}$$\end{document} for the amplitude of the input voltage is 125 mV under the condition that the frequency of the sinusoidal input voltage is 100 Hz. The power consumption, the input referred noise, and the frequency characteristics are not deteriorated even using the proposed technique. The simulation results show the validity and availability of the proposed transconductor.