Large-signal analysis of substrate effects in RF-power SOI-LDMOS transistors

Large-signal analysis of RF-power SOI-LDMOS transistors has been done on devices with different substrates resistivities. The effect of substrate resistivity on efficiency and output power has been investigated in class-AB operation and especially the loss mechanisms are studied. The large-signal performance is compared with the small-signal performance in an attempt to couple those parameters more tightly to each other. It is shown that the resistivity has great impact on the efficiency of the devices and the differences are related to losses in the substrate. The result verifies earlier indications that either a very high or very low substrate resistivity is beneficial to minimize the substrate losses. The study also shows interesting connections between the small-signal output resistance and capacitance and their large-signal counterparts derived from optimum load impedances.