# Missing contamination delay specification for a component

If IIUC: contamination delay ($$\t_{cd}\$$) is the time where the signal level on the output of a component starts to change in response to a change on the component's input, while the propagation delay ($$\t_{pd}\$$) is where this signal level change on the output stabilizes (i.e. becomes valid). Furthermore $$\t_{cd,min}\$$ of a component must be bigger than the maximum hold time of a subsequent component connected to the first component's output.

While all component specifications I found provide $$\t_{pd,max}\$$ none of them provided $$\t_{cd,min}\$$. What is the reason for this? Can I assume in this case that $$\t_{cd,min} = t_{pd,max}\$$ ?

No, but $$\t_{pd(min)}\$$ is the same thing as your $$\t_{cd(min)}\$$.
• Ok, it makes sense that we can assume that $t_{cd(min)}$ is $t_{pd(min)}$ or 0 if the latter is not specified. I'd like to note that there seems to be a valid reason for differentiating between $t_{cd}$ and $t_{pd}$. The former would mark the delay where the output signal level becomes invalid (used to check against hold time violations), while the latter marks the delay where the output signal level becomes valid (used to check against setup time violations). The min,typ,max values would just mark the min,typ,max delays for each of these distinct events. – Imre Deák Sep 27 '19 at 20:04
• I understand the distinction you're making, but in practical terms, there's no real use for $t_{pd(min)}$ other than to mean the same thing as $t_{cd(min)}$ -- you can't base your design on the earliest time a signal might become valid. Therefore, it has always been understood that the minimum propagation delay means the exact same thing as "output hold time" -- what you're calling "contamination delay". – Dave Tweed Sep 27 '19 at 20:21