# Resistor

In this topic:

## Netlist Entry

Rxxxx n1 n2 [model_name] [value] [L=length] [W=width] [ACRES=ac_resistance]
[TEMP=local_temp] [TC1=tc1] [TC2=tc2] [M=mult] [DTEMP=dtemp]
 n1 Node 1 n2 Node 2 model_name (Optional) Name of model. Must begin with a letter but can contain any character except whitespace and '.' value Resistance (W) length Length of resistive element in metres. Only used if value is omitted. See notes below width Width of resistive element in metres. Only used if value is omitted. See notes below ac_resistance Resistance used for AC analyses and for the calculation of thermal noise. If omitted, value defaults to final resistance value. local_temp Resistor temperature (˚C) tc1 First order temperature coefficient tc2 Second order temperature coefficient mult Device multiplier. Equivalent to putting mult devices in parallel. dtemp Differential temperature. Similar to local_temp but is specified relative to circuit temperature. If both TEMP and DTEMP are specified, TEMP takes precedence.

## Notes

• If model_name is omitted, value must be specified.
• If model_name is present and value is omitted, length and width must be specified in which case the value of the resistance is RES * RSH * L/W where RSH is the sheet resistance model parameter and RES is the resistance multiplier. See model parameters below. If ACRES is specified and non-zero its value will be used unconditionally for AC analyses and the calculation of thermal noise.

## Resistor Model Syntax

.model modelname R ( parameters )

## Resistor Model Parameters

 Name Description Units Default RES Resistance multiplier 1 TC1 First order temperature coefficient 1/° C 0 TC2 Second order temperature coefficient 1/° C2 0 RSH Sheet resistance Ω/sq 0 KF Flicker noise coefficient m2/Ω2 0 EF Flicker noise exponent 1 TNOM, T_MEASURED Reference temperature; the temperature at which the model parameters were measured ° C 27 T_ABS If specified, defines the absolute model temperature overriding the global temperature defined using .TEMP ° C .TEMP T_REL_GLOBAL Offsets global temperature defined using .TEMP. Overridden by T_ABS ° C 0.0

## Notes

The flicker noise parameters are proprietary to SIMetrix. Flicker noise voltage is: $V_n^2 = \text{KF} \cdot \text{RSH}^2/(L\cdot W) \cdot V_r^2 \cdot \Delta f/f^{\text{EF}}$

Where:
• $Vr$ = Voltage across resistor.

The equation has been formulated so that KF is constant for a given resistive material.

If one of L, W is not specified, the flicker noise voltage becomes:

$V_n^2 = \text{KF} \cdot \text{R}^2 \cdot V_r^2 \cdot \Delta f/f^{\text{EF}}$

Where R is the final resistance.

i.e. the noise current is independent of resistance. This doesn't have any particular basis in physical laws and is implemented this way simply for convenience. When resistor dimensions and resistivity are unavailable, the value of KF will need to be extracted for each individual value.