Some issues in high frequency noise modeling of MOSFETs

This paper presents two of the important issues in high frequency noise modeling of MOSFETs—the determination of the channel thermal noise and the removal of the pad effects. First, an extraction method to obtain the channel thermal noise in MOSFETs directly from d.c., scattering (s-) and noise parameters measurements is discussed. In this method, the transistor’s transconductance (gm), output resistance (RDS) and source and drain resistances (RS and RD) can be extracted from d.c. measurements. Its gate resistance (RG) is extracted from s-parameter measurements, and the equivalent noise resistance (Rg) is obtained from RF noise measurements at low frequencies. With these quantities known, the channel thermal noise can then be directly calculated. Second, for short-channel length MOSFETs, the effects of the pads can significantly distort the transistor’s noise parameters. Ideas on how this can be removed by appropriate experiments are described. Appropriate test structures for removing the effects of the pads’ parasities are discussed.