An analysis of small-signal source-body resistance effect on RF power MOSFETs for 5-GHz band WLAN applications

In this paper, a comprehensive analysis of the effects of various source-to-body spacing, reverse body bias, and device layout on the device´s S-parameters, noise parameters, and power performances are demonstrated. Our results show that for RF MOSFETs, the input impedance and output impedance can be represented by a series RC circuit at low frequencies and a parallel RC circuit at high frequencies. The appearance of the kink phenomenon of scattering parameters S₁₁ and S₂₂ in a Smith chart is caused by this inherent ambivalent characteristic of the input and output impedances. It was found that an increase of source-to-body spacing enhances the kink phenomenon of S₁₁ and S₂₂, but deteriorates the RF noise and power performances mainly due to the increase of substrate resistance R_sub2 of the devices. In addition, the kink phenomenon of S₁₁ and S₂₂ becomes more obscure as reverse body bias increases. The present analyses enable RF engineers to understand the S-parameters, noise parameters, and power performances of RF power MOSFETs more deeply, and hence are helpful for them to create a fully scalable RF power CMOS model for SOC applications.