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Improved negative capacitance circuit stable with a low gain margin  

김영필 (대전대학교 전자공학과)
황인덕 (대전대학교 전자공학과)
Publication Information
Journal of the Institute of Electronics Engineers of Korea SC / v.40, no.6, 2003 , pp. 68-77 More about this Journal
Abstract
An improved negative capacitance circuit that cancels out input impedance of a front-end in a bioimpedance measurement and operates stably with a low gain margin has been proposed. Since the proposed circuit comprises wide-band operational amplifiers, selecting operational amplifiers is easy, while an operational amplifier of prefer bandwidth should be chosen to apply conventional circuit. Also, since gain margin can be controlled by a feedback resistor connected serially with a feedback capacitor, gain margin is tuneable with a potentiometer. The input impedance of the proposed circuit is two times larger than that of the conventional circuit and 40-times than that without a negative capacitance circuit. Furthermore, closed-loop phase response of the proposed circuit is better than that of the conventional circuit or without a negative capacitance circuit. Above all, for the proposed circuit, the frequency at which a gain peaking occurs is higher than the frequency at which the loop gain becomes a maximum. Thus, the proposed circuit is not affected by a gain peaking and can be operated with a very low gain margin.
Keywords
bioimpedance; input capacitance; negative capacitance; input impedance; positive feedback;
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