Considerations on the RLC model of CMOS transistor only simulated inductors

A study of the classical RLC equivalent passive model for CMOS transistor only simulated inductors (TOSI) is presented. The model is compared with a four branches RLC model and its frequency performances and limitations are discussed. The analysis is applied on a particular active inductor topology for frequencies between 0.45 GHz and 3.3 GHz, the study being focused on the resonant frequency and inductance value. As simulations show, the model accuracy is strongly dependent on transistor parasitics and device modeling. It is shown that the second model is more accurate regarding the inductance value while the classical one is helpful for simplified calculus with respect to the resonant frequency. These considerations are valid in case of using charge based transistor model only. The simulations were carried out in 0.35μm AMS CMOS process.