# 11.2.5. Parameters

Design parameters are the ones the designer can tune in order to satisfy the design requirements.

For every design parameter you must specify its initial value. For design parameters that will be tuned by the optimizer you must also specify the lower and the upper bound.

Operating parameters define the environment in which the circuit operates.
Typically a circuit must satisfy the design requirements across a range
of operating parameter values. Therefore every operating parameters
requires a nominal value which must lie within the interval specified by
the lower and the upper bound. Circuit temperature is a special parameter
in PyOPUS simulators. It is accessed as the `temperature`

netlist
parameter.

Statistical parameters are the ones that vary randomly. A designer has
little or no influence on these parameters. Two statistical parameters are
defined for every MOS transistor instance in file `mosmm.inc`

. For transistor
xmn1 the two parameters are accessible as mn1vt and mn1u0 netlist parameters
(they were generated by the netlister when the Miller opamp definition was
netlisted). These parameters are supposed to be independent normally
distributed random variables with zero mean and variance one. They model the
random variations which give rise to the mismatch effect.

A designer can reduce mismatch by increasing the transistor area which reduces the magnitude of random variations. If we want to simulate a circuit that has no random variations these parameters should be set to zero.

Additionally four more statistical parameters are defined in the Monte Carlo
MOS transistor model (gvtnmm, gu0nmm, gvtpmm, and gu0pmm). They are also
supposed to be independent normally distributed random variables with zero
mean and variance one. They represent the global process variations which
affect all transistors of the same type in the same way. We list them among
statistical parameters although they are not required by the netlist if we
use a MOS transistor model other than `mc`

(i.e. Monte Carlo model).

Statistical parameters are currently not used in the GUI because none of the analyses that requires them is supported at this point. Nevertheless, they are added to the simulator’s input netlist if they are defined.

All parameter names must be unique identifiers.