JFET and MESFET Noise Models

Noise Parameters

Noise Equations

The JFET noise model is shown in JFET/MESFET AC Noise Analysis. Thermal noise generation in the drain and source regions (RD and RS resistances) is modeled by the two current sources, inrd and inrs. The units of inrd and inrs are:

Channel thermal 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 previous 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 is physically impossible. If the 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

, Linear region

Saturation region

The flicker noise is calculated as:

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