## 3.18 `R`: Resistor

### 3.18.1 Syntax

`R` xxxxxxx n+ n– value
`R` xxxxxxx n+ n– expression
`R` xxxxxxx n+ n– model {`L=`length} {`W=`width} {`TEMP=`temperature}
`.RESistor` label n+ n– expression

### 3.18.2 Purpose

Resistor, or general current controlled dissipative element.

### 3.18.3 Comments

N+ and n– are the positive and negative element nodes, respectively. Value is the resistance in Ohms.
The resistor (type `R`) differs from the admittance (type `Y`) in that the resistor is a current controlled element, and the conductance is a voltage controlled element, in addition to the obvious use of conductance (1/R) instead of resistance.
You may specify the value in one of three forms:

1. A simple value. This is the resistance in Ohms.
2. An expression, as described in the behavioral modeling chapter. The expression can specify the voltage as a function of current, or the resistance as a function of time.
3. A model, which calculates the resistance as a function of length and width, referencing a `.model` statement of type `R`. This is compatible with the Spice-3 “semiconductor resistor”.

### 3.18.4 Model statement

A model statement may be used,, with model type `R` or `Res`. The parameters are:

`RSH` = x
  Sheet resistance. (Ohms / square). (Required)
`CJSW` = x
  Junction sidewall capacitance. (Farads / meter). (Default = 0.)
`DEFW` = x
  Default width. (meters). (Default = 1e-6)
`NARROW` = x
  Narrowing due to side etching. (meters). (Default = 0.)
`TC1` = x
  First order temperature coefficient. (Farads / degree C). (Default = 0.)
`TC2` = x
  Second order temperature coefficient. (Farads / degree C squared). (Default = 0.)
`TNOM` = x
  Parameter measurement temperature. (degrees C.). (Default = 27.)

Resistance is computed by the formula:

    resistance = RSH * (L - NARROW) / (W - NARROW)

After the nominal value is calculated, it is adjusted for temperature by the formula:

    value *= (1 + TC1 * (T-T0) + TC2 * (T-T0)^2)