A DC-4-GHz true logarithmic amplifier: theory and implementation

Abstract

His current research interests include linear RF power amplifiers and nonlinear systems. R. Douglas Beards (M'95) received the B.Eng. (with high distinction) and M.Eng. degrees in electrical engineering from Carleton University, Ottawa, ON, Canada, in 1988 and 1990, respectively. He has spent his entire career with Nortel Networks, Ottawa, involved with the design of bipolar and BiCMOS RF integrated circuits for wireless communications. A. J. Bergsma received the B.Eng. and M.Eng. degrees in electrical engineering

A new CMOS logarithmic current generator

“…Many approaches to the design of logarithmic circuits have been reported in the literature [1][2][3][4][5][6][7] and the references cited therein. The authors did not find references to a CMOS current-mode logarithmic circuit in the open literature except for the one reported in [2].…”

“…All other realizations found in the literature have at least one of the following drawbacks: absence of low voltage operation capability [1,3,5], limited dynamic range [1,3,6], employment of BJT transistors [1,5,6], does not enjoy current-mode [1,3,4,6], cannot realize a true logarithmic function circuit where the ratio is larger or smaller than unity [1,6,7], temperature dependent [1,5], relatively high power consumption [6,7], no gain controllability [1,3,6], to some extent linearity error is high [3,6,7], uses passive elements, i.e. resistors [1,5,6], and finally design complexity [6,7].…”

Analysis and design of the true piecewise approximation logarithmic amplifiers

“…Logarithmic amplifiers convert an input signal with a wide dynamic range into an output signal with a determined range [1][2][3][4][5][6][7][8][9][10][11]. Logarithmic amplifiers are widely used in numerous receiving systems to compress the high dynamic range of the received signals.…”

“…True logarithmic amplifiers provide the logarithm of the signal without demodulating, but the demodulating ones detect the logarithm of the envelope of the signal [2]. In true logarithmic amplifiers, the phase shift or delay through the logarithmic amplifier do not vary with the input signal level.…”

“…On the basis of the circuit technique and architecture, the logarithmic amplifiers are subdivided into the single stage and piecewise approximation types [2]. Single stage types use the exponential characteristics of the semiconductor devices such as p-n junction diodes [15], light emitting diodes [16], photo diodes [17], bipolar transistors [18], GaAs MESFETs [19], and MOS transistors in the subthreshold region [20] to create the logarithmic curve.…”