Friday, January 29, 2010

Transport and Inertial Delay

Delays are usually used for behavioral models to better represent signaling at their external interface.The main difference is that transport delay adds the propagation delay to the signal. How ever the inertial delay causes the pulses less than that delay to get suppressed & will not propagate these pulses to change the output.

Inertial Delay
Inertial delay.inertial delay is the one which gate ( Component ) have,that is if a gate is modeling then in real situation it has some delay to model that inertial delay is used. For example If you model an inertial delay of, say 20 ns, and then put a pulse of, say, 10ns, through the model, it will be "swallowed" and will not appear at the output. Because I/p pulse that do not exceed the propagation delay of the gate do not propagate to the O/P.
Inertial delay is the time it takes for a signal to change its value.
This is usually representative of capacitance.The continuous-assignment will create an inertial delay.
By default delay is inertial.

Transport delay
It's the time taken by signal to propagate through a net i.e through wire also known as time of flight

transport delay is the delay of a wire. if you model a transport delay of  20ns, and then put a pulse of 10ns then it will appear after delayed by the 20ns. it is simply wire delay delay will increase more and more when wire length increases means it can vary.


Nice explanation given by some of the authors

Verilog Example

VHDL example