Optimum SOI device and circuit design methodologies for RF switch and digitally programmable capacitor applications

Abstract

This work presents optimum design methodology of SOI-CMOS high power RF switch and digitally programmable capacitor array (DPCA) using it for future flexible/reconfigurable RF front-end modules (FEMs). High power RF switch is a key building block for reconfigurable RF front-end circuits such as tunable impedance matching network, tunable duplexer/filter, and tunable power amplifier as well as time division duplexing (TDD) RF system. The most stringent specifications for high power RF switch are power handling capability and harmonic distortion performances. To establish systematic design procedure for high power RF switch, MOSFET parameters affecting RF performances are studied in the first. Especially, since there are no analytical study on large signal MOSFET characteristics limiting power handling capability and harmonic distortions, we carefully deal with MOSFET characterization and optimization method for maximum power handling capability and MOSFET originated harmonic distortion analysis. The dominant reason to limit the power handling capability is undesirable channel formation on off-state FETs in the event of a large signal input. This undesirable channel formation appears as a significant amount of leakage current such as gate induced leakage current (GIDL), lateral bipolar latch-up, and source-drain punch-through. To characterize leakage current and find correlation between DC I-V measurement and $RF P_{1dB}$ measurement, new DC characterization method (Float FET I-V characterization method) reflecting RF switch operation is proposed. Based on proposed FFI-V method, the experimental study on optimum dc bias point, MOSFET device design, and stacked-FETs device design is performed to maximize the power handling capability of RF switch. For MOSFET device originated harmonic distortions, main contributions are classified into two categories: 1) voltage dependent off-state capacitance ($C_{off}$) nonlinearity and 2) on-state resistance ($R_{on}$) nonlin...