A 2-Port Stable Negative Capacitance Circuit Design With Unilateral Gain Boosting Technique

Herein, we present a floating 2-port nonreciprocal negative capacitance (NCAP) circuit that employs a unilateral gain boosting technique by including an asymmetric cross-coupled differential cascode transistor pair. The proposed circuit provides an asymmetric gain characteristic. The forward gain ( $S_{21}$ ) is increased at the cost of the backward gain ( $S_{12}$ ). The technique not only provides a boosted forward gain but also stable operation resulting from this reduced backward gain. We further investigate the stability of the NCAP circuit in terms of the output resistances of the current sources in the circuit. The proposed NCAP circuit was implemented in IBM 7RF 180-nm CMOS technology and was designed to have a supply voltage of 3 V and a current of 10 mA. The S-parameter measurements showed a self-resonance frequency of 2.25 GHz. The maximum $S_{21}$ was −0.2 dB at 1 GHz. In the frequency range from 0.5 to 1.5 GHz, the capacitance was approximately −4 pF, and the difference between $S_{21}$ and $S_{12}$ was 8.7–9.6 dB. The size of the core chip was $150 \times 190~\mu \text{m}^{2}$ .