Selective metal parallel shunting inductor and its VCO application

For a planar inductor, the maximal quality factor, Q_max, is located at the specified frequency, f_Qmax. In this paper, a method called selective metal parallel shunting (SMPS) is proposed to move f_Qmax onto the desired frequency without additional processing steps. For a given planar inductor, a customized program is developed to find all the possible SMPS inductors and predict their Q_max and f_max. Three sets of planar, all metal parallel shunting (AMPS), and SMPS inductors have been implemented in a 1P4M 0.35 μm CMOS process to verify the proposed method. The prediction errors of Q_max and f_Qmax are less than 13% and 10%, respectively, between the simulated and measured ones. Moreover, three 2.3-2.4 GHz VCOs using planar, AMPS, and SMPS inductors, respectively, have also been realized. The phase noise of the VCO using SMPS inductors can be improved by 9.3 dB and 6 dB, respectively, compared to the VCOs using planar and AMPS inductors at 100 KHz offset frequency. The figure-of-merit (FOM) performance of the VCO using SMPS inductors can be comparable to the state-of-the-art publications.