11.2.5. Parameters

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

Setting up the design parameters.

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.

Setting up the operating parameters.

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.

Setting up the statistical parameters.

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.