Using Noise Models

This section describes how to use noise models.

Using Noise Parameters

Using Noise Equations

The Star-Hspice MOSFET model noise equations have a selector parameter NLEV that is used to select either the original SPICE flicker noise or an equation proposed by Gray and Meyer.

Thermal noise generation in the drain and source resistors is modeled by the two sources inrd and inrs (units amp/(Hz) 1/2 ), as shown in Equivalent Circuit, MOSFET AC Noise Analysis. The values of these sources can be determined by:

Channel thermal noise and flicker noise are modeled by the current source ind and defined by the equation:

If the model parameter NLEV is less than 3, then

The above formula is used in both saturation and linear regions, which can lead to wrong results in the linear region. For example, at VDS=0, channel thermal noise becomes zero because gm=0. This calculation is physically impossible. If NLEV model parameter is set to 3, Star-Hspice uses a different equation which is valid in both linear and saturation regions. See Tsivids, Yanis P., Operation and Modeling of the MOS Transistor, McGraw-Hill, 1987, p. 340.

For NLEV=3,

where

The two parameters AF and KF are used in the small-signal AC noise analysis to determine the equivalent flicker noise current generator connected between drain and source.

NLEV=0 (SPICE):

For NLEV=1 the Leff 2 in the above equation is replaced by Weff · Leff.

NLEV=2, 3:

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