An analysis of small-signal source-body resistance effect on RF MOSFETs for low-cost system-on-chip (SoC) applications

In this paper, we demonstrate a comprehensive analysis of small-signal source-body resistance (R_sb) effect on the RF performances of RF MOSFETs for low-cost system-on-chip (SoC) applications for the first time. Our results show that for RF MOSFETs, both the kink phenomena of S₁₁ and S₂₂ become more obscure as reverse body bias (V_B) increases due to the decrease of transconductance (g_m). In addition, an increase of source-body spacing enhances both the kink phenomena of S₁₁ and S₂₂, but deteriorates the current-gain cut-off frequency (f_T), maximum oscillation frequency (f_MAX), and RF noise and power performances due to the increase of R_sb of the devices. Analytical formulas are derived to explain the kink phenomena of S₁₁ and S₂₂, and to explain why increasing R_sb leads to a reduction of equivalent substrate resistance R_sub, or worse f_T, f_MAX, and RF noise performances of the devices. The present analyzes enable RF engineers to understand the S-parameters, noise parameters, and power performances of RF MOSFETs more deeply, and hence are helpful for them to optimize the layout of MOSFETs and to create a fully scalable RF CMOS model for SoC applications.