Definitions related to Delays

[Harinath Renukamurthy]

Dear All,
Here are some things to remember when it comes to delays:

Symbol -->    Name

1. TR  --> Rise Time
2. TF  --> Fall Time
3. TPLH  --> Rise Delay
4. TPHL  ---> Fall delay


Rise time and Fall time exists for any digital signal, both input signal and output signals.

Rise Time, TR: Measured as time taken to reach from 10% to 90% of the final HIGH value

Fall Time, TF: Measured as time taken to reach from 10% to 90% of the final LOW value

(The percentage can be from 20% to 80% or 25% to 75% depending on the technology node the designer's choice)

Rise Delay, TPLH: Time between 50% of input waveform to 50% of output waveform when the output is rising (zero to one)


Rise Delay, TPLH: Time between 50% of input waveform to 50% of output waveform when the output is falling. (one to zero)


A flip-flop has additional parameters:

Setup, TS:  The minimum time when D-input should be stable before the clock edge occurs

Hold, TH:  The minimum time when D-input should be stable after the clock edge occurs

For a flip-flop to function correctly both setup and hold time requirements have to be met.

I hope this helps.

Best Regards,
Harinath