Using Noise Models

This section describes how to use noise models.

Using Noise Parameters

Name (Alias)







Flicker noise exponent




Flicker noise coefficient. Reasonable values for KF are in the range 1e-19 to 1e-25 V 2 F.




Noise equation selector




Channel thermal noise coefficient (use with NLEV=3)

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,




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.



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

NLEV=2, 3:


Noise Summary Printout Definitions

RD, V2/Hz

Output thermal noise due to drain resistor

RS, V2/Hz

Output thermal noise due to source resistor


Transfer function of channel thermal or flicker noise to the output. This is not a noise, it is a transfer coefficient, reflecting the contribution of channel thermal or flicker noise to the output.

ID, V2/Hz

Output channel thermal noise: ID = RX2· (channel thermal noise)2

FN, V2/Hz

Output flicker noise: FN = RX2· (flicker noise)2

TOT, V2/Hz

Total output noise: TOT = RD + RS + ID + FN

Star-Hspice Manual - Release 2001.2 - June 2001