You don't need to, if there is any, should have been defined in the techonology library. Sometime you might want to set max transition transition constraints for performance purpose.
Design rules are provided in the vendor technology library
to ensure that the product meets specifications and works
as intended. Typical design rules constrain transition times
(set_max_transition), fanout loads (set_max_fanout), and
capacitances (set_max_capacitance). These rules specify
technology requirements that you cannot violate.
(You can, however, specify stricter constraints.)
The max_fanout/max_transition/max_capacitance is limited in the library. It is a hard limiting.
In the design, you may limit them in the max range.
such as , need the high frequency , you may limit the max fanout < 4(3), max_transition < 1/10*cycle peroid, max_capacitance < 4 unit cell area.
The max_fanout/max_transition/max_capacitance is limited in the library. It is a hard limiting.
In the design, you may limit them in the max range.
such as , need the high frequency , you may limit the max fanout < 4(3), max_transition < 1/10*cycle peroid, max_capacitance < 4 unit cell area.
The value of these parameters is from the library you adopted, and it have no relevancy with your design, but you could set a stricter value according your design.
Typical design rule scenarios are
• set_max_fanout and set_max_transition commands
• set_max_fanout and set_max_capacitance commands
Typically, a technology library specifies a default max_transition or max_capacitance, but not both. To achieve the best result, do not mix max_transition and max_capacitance.
You can edit the target library for example vi tsmc25_typ.lib and you will see many table in library, the two dimionsation of table is transition time and load capacitance, so accroding to your timing you can to define what capacitance, transition is good for your design.
I think the more transition time is, the more duration NMOS and PMOS are both working and large current will last more time. so Power is much more in transition time.