On the validity of conventional MOSFET nonlinearity characterization at RF switching

We analyze the linearity of metal oxide semiconductor field effect transistors (MOSFETs) at radio frequency switching using the conventional extraction method of IP3, measured harmonic distortion (HD), and a surface-potential-based MOSFET model for circuit-simulation. The applicability of the conventional extraction method of IP3 at low frequency to represent IP3 at high frequency is also investigated. At low frequency, measured HD characteristics and extracted IP3 values correspond to the prediction by the model which adopts the quasistatic approximation, i.e., instantaneous carrier response is assumed. Beyond half of the cutoff frequency, the carrier response delay enhances the MOSFET nonlinearity, which is manifested by a decreased first order harmonic and a pronounced curvature of the third order harmonic. Consequently, the conventional extraction method of IP3 value from the intersection point of linearly extrapolated first and third harmonics becomes unreliable