A 1-V Continuous-Time Filter Using Bipolar Pseudo-Differential Transconductors

Fujihiko MATSUMOTO  Yasuaki NOGUCHI  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E82-A   No.6   pp.973-980
Publication Date: 1999/06/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section of Papers Selected from 1998 International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC '98))
analog integrated circuit,  continuous-time filters,  transconductors,  low voltage analog circuits,  common-mode rejection ratio,  

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Low-voltage technique for IC is getting one of the most important matters. It is quite difficult to realize a filter which can operate at 1 V or less because the base-emitter voltage of transistors can hardly be reduced. A design of a low-voltage continuous-time filter is presented in this paper. The basic building block of the filter is a pseudo-differential transconductor which has no tail current source. Therefore, the operating voltage is lower than that of an emitter-coupled pair. However, the common-mode (CM) gain of the transconductor is quite high and the CMRR is low. In order to reduce the CM gain, a CM feedback circuit is employed. The transconductance characteristic is expressed as the function of hyperbolic cosine. The designed filter is a fifth-order gyrator-C filter. The transconductor and the filter which has a fifth-order Butterworth lowpass characteristic are demonstrated by PSpice simulation. Transconductance characteristic, CMRR and stability of the transconductor are confirmed through the simulation. In the analysis of the filter, frequency response and offset voltage are examined. It is shown that the filter which has corner frequency of the order of megahertz can operate at a 1 V supply voltage.