Overcome the phase noise optimization limit of differential LC oscillator with asymmetric capacitance tank structure [CMOS RFIC]

A phase noise optimization method, with an asymmetric capacitance tank structure, is proposed, which overcomes the shortcomings of the previous tank L/C ratio optimization approach. The proposed phase noise optimization method, with asymmetric capacitance tank structure, can be applied to the complementary Colpitts (c-Colpitts) oscillator. The phase noise characteristics of the c-Colpitts explain well the excellence of an asymmetric tank structure, and the phase noise properties are proved by simulation and experiment. Moreover, a differentially coupled c-Colpitts oscillator topology is proposed, which can achieve a better phase noise performance than that of the conventional differential LC oscillator.