Design and Analysis of a CMOS Moore Fractal MOM Capacitor With an Application to an RF Active Image Reject Filter

Design and analysis of a metal-oxide-metal (MOM) capacitor in 0.18-
$\mu \text{m}$
RF CMOS process, suitable for the
${L}$
-,
${S}$
-, and
${C}$
-band integrated circuits, is presented in this article. In order to maximize the flux density per unit area, Moore fractal geometry is chosen for the capacitor plates. The capacitor uses lateral electric fields, in contrast to commonly used vertical electric fields. To further increase the capacitance density, four metal layers of the CMOS process are used by efficient contact of vias. The design strategy makes it possible to achieve a high value of capacitance and
${Q}$
factor, noted as 1.15 pF and 51.6, respectively, at 2.4 GHz, for a silicon area of 65
$\times \,\,65\,\,\mu \text{m}^{{2}}$
. The obtained self-resonance frequency is 13.5 GHz. A variability analysis is done and parasitics are extracted using a high-frequency capacitor circuit model. An active, third-order image reject filter (IRF) is subsequently realized as a circuit application for the designed fractal capacitor. The filter provides a notch at 1.8 GHz with more than 35-dB attenuation and a controlled passband centered at 2.4 GHz.