Selective Metal Parallel Shunting Inductor and Its VCO Application

The methodology to calculate the parasitic capacitances in differential symmetric inductors will be presented in this paper. Inspired by the proposed methodology, a method called selective metal parallel shunting (SMPS) can move f(Qmax) onto the desired frequency without additional processing steps. Based on the proposed methodology, a customized program is developed to predict Q(max) s and f(Qmax) s of on-chip inductors. Differential symmetric inductors and spiral ones with planar, all metal parallel shunting (AMPS), and SMPS configurations have been implemented in a 1P4M 0.35-(mu)m CMOS process to verify the proposed method. Moreover, three 2.3–2.4 GHz voltage-controlled oscillators (VCOs) using planar, AMPS, and SMPS inductors, have also been realized. The phase noise of the VCO using SMPS inductors can be improved by 9.3 and 6 dB at 100-kHz offset frequency, respectively, compared to the VCOs using planar and AMPS inductors. The proposed SMPS technique can not only be applicable to VCO but also other RF circuits.