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We propose a wideband lumped element directional coupler using lossy negative capacitance (NCAP). NCAP provides a broadband resonance effect combined with passive inductors and capacitors in a circuit, enabling the coupler to exhibit wideband directivity performance. In addition, a 3-dB loss in the NCAP enhanced the bandwidth at the expense of the transmission gain, which decreased by only 0.3 dB. The proposed coupler was implemented in the IBM 7RF 180-nm CMOS technology. The size of the core chip is $1180\,\,\mu \text {m} \times 570\,\,\mu \text{m}$ . The designed NCAP provides a capacitance of −13 pF using a supply voltage of 2.7 V and a current of 9.6 mA. The coupling was designed to be −10 dB at the center frequency of 1 GHz. The bandwidth was defined by the frequency range, which exhibited a directivity of more than 30 dB. The S-parameter measurements showed an absolute bandwidth ranging from 0.86 to 1.12 GHz, and a fractional bandwidth of 26%. In the bandwidth, the coupling had a 0.5-dB variation, the transmission loss was smaller than 2.14 dB, and the noise figures were 1.8–2.5 dB.

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 $150 \times 190~\mu \text{m}^{2}$ .