The two main sources of low-frequency flicker noise are mobility fluctuations and number fluctuations. Our experiments on NMOS noise measurements were done from subthreshold to saturation region of operation for both long-channel (5 /spl mu/m) and short-channel (as small as 0.6 /spl mu/m) NMOS transistors. The results suggest that for both types that in the saturation region, the flicker noise is due to the surface state effect and the noise equations, NLEV=2 and 3, in SPICE, HSPICE, and PSPICE are most appropriate. For short-channel devices, due to the effects of velocity saturation and the resulting nonlinear transconductance (g/sub m/) variation with gate bias voltage, the input-referred voltage noise increases as the gate-source voltage increases instead of staying constant as it does for long-channel devices. In the subthreshold region, the input-referred voltage noise decreases drastically as the gate-source voltage increases for both long-channel and short-channel NMOS devices. Simulations have been done using PSPICE and HSPICE, with noise level (NLEV)=3 and device model level 3 and BSIM 3.2 and 3.3. The results from PSPICE version 8.0 level 7 (BSIM 3.3) and SPICE level 3 compare favorably with the measured noise phenomena for the short-channel and long-channel NMOS devices, respectively.

This report describes a successful simulation using HSPICE and comparison with published data of the phase noise on a 2-GHz CMOS inductance-capacitance (LC) oscillator caused by low-frequency flicker noise (1/f noise). The flicker noise, which is determined by measurements on NMOSFETs, is simulated as a sum of sine waves with random phase by using MATLAB, and is finally introduced into the LC oscillator circuit as an HSPICE piecewise linear waveform. The output of LC oscillator in HSPICE is written as a series of points equally spaced in time and then the spectrum is computed by fast Fourier transform (FFT). The simulation results show the phase noise of the voltage-controlled oscillator with different noise coefficient (KF) values in the SPICE models, and demonstrate that the phase noise caused by low-frequency flicker noise has a 1/f/sup 3/ dependence on the offset frequency. The simulated sideband power spectral density corresponds to the measured values reported in the literature.