Can a net have negative propagation delay?

As we discussed in ‘’Is it possible for a logic gate to have negative propagation delay”, a logic cell can have negative propagation delay. However, the only condition we mentioned was that the transition at the output pin should be improved drastically so that 50% level at output is reached before 50% level of input waveform.

In other words, the only condition for negative delay is to have improvement in slew. As we know, a net has only passive parasitic in the form of parasitic resistances and capacitances. Passive elements can only degrade the transition as they cannot provide energy (assuming no crosstalk); rather can only dissipate it. In other words, it is not possible for a net to have negative propagation delay.

However, we can have negative delay for a net, if there is crosstalk, as crosstalk can improve the transition on a net. In other words, in the presence of crosstalk, we can have 50% level at output reached before 50% level at input; hence, negative propagation delay of a net.

Also read:

• Bubble errors and bubble error correction
• Noise margins
• Can hold be frequency dependant
• Worst slew propagation
• Latchup in CMOS devices