User`s guide

Timin
g
Characteristics 7
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Timin
g
Characteristics
A digital device model’s timing behavior can be defined in one
of two ways:
• Most primitives have an associated Timing Model, in which
propagation delays and timing constraints (such as setup/
hold times) are specified. This method is used when it is
easy to partition delays among individual primitives;
typically when the number of primitives is small.
• Use the PINDLY and CONSTRAINT primitives, which can
directly model pin-to-pin delays and timing constraints for
the whole device model. With this method, all other
functional primitives operate in zero delay.
In addition to explicit propagation delays, other factors, such as
output loads, can affect the total propagation delay through a
device.
Timin
g
Model
With the exception of the PULLUP, PULLDN, and PINDLY
devices, all digital primitives have a Timing Model which
provides timing parameters to the simulator. The Timing Model
for each primitive type is unique. That is, the model name and
the parameters that can be defined for that model vary with the
primitive type.
Within a Timing Model, there may be one or more types of
parameters:
• Propagation delays (TP)
• Setup times (TSU)
• Hold times (TH)
• Pulse widths (TW)
• Switching times (TSW)
Each parameter is further divided into three values: minimum
(MN), typical (TY), and maximum (MX). For example, the
Refer to the online MicroSim
PSpice A/D Reference Manual
for a detailed discussion on
these two primitives.