For resistors, capacitors, inductors and DC generators, tolerance values can be specified directly in the SPICE attributes of the component by specifying a value for the TOLERANCE parameter. This mode is useful for including tolerance values directly in component libraries. Tolerance specifications have the following form:
 Syntax: |
|---|
| [DEV [/<group>] [/<distribution>] <value>[%]] [LOT [/<group>] [/<distribution>] <value>[%]] |
You can specify the DEV tolerance or the LOT tolerance, or both. In the latter case, the tolerance values are calculated independently and added together. The combination of the DEV and LOT tolerances is useful for situations where component variations are not completely correlated, but are not even completely independent of each other. For example, in a resistive network you can have a LOT tolerance referred to the component and a smaller DEV tolerance referred to the variations of the individual resistors.
Each tolerance type is defined by the following three parameters:
Value |
It can be specified both as an absolute value and as a percentage by adding the suffix %. For example, for a 1000 ohms resistor if you specify a tolerance of 10, you will get a variation between 990 and 1010 ohms, while if you specify 10% you will get a variation between 900 and 1100 ohms. |
Group |
You must assign the same group number to multiple components when you want their tolerance variations to be correlated, i.e. the values increase or decrease jointly. If you specify the zero group then the value of the component varies independently of all other components. Groups 1 to 15 are available. This parameter is optional. |
Distribution |
Specify the type of statistical distribution to use. You must specify UNIFORM for uniform distribution, GAUSS for the Gaussian distribution, and WCASE for the worst case distribution. It is also possible to indicate only the initial letter. This parameter is optional. |