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# what happens if hold time greater than setup time

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#### kil

##### Member level 5
hi all
i have a question for all plz hgelp me

what happens when hold time (15nsec) greater than setup time (3nse)
then whether we can abale to calculate the clock frequency when propagation dealy is provided (say 4nsec) .............

my dout is what will happen whe hold time is far more than setup time

if u have any sequential circuits for calculating setup time clock freq and other timing things for interviews plz do forward me

or plz suggest some good sites for them

krushi

I think in general hold time and setup time are un-corelated ! to each other!

I think there is no relation between setup and hold time

for normal flop to flop path i.e.

FF1 --> Combinational logic with delay (td) --> FF2

if FF1/FF2 clock to q delay is tcq and set up and hold time are ts and th then basic equations are

tc > tcq + td + ts
th < tcq + td

This is the base of all flop base designs.
:idea:

How can i find value of ts ? is it setup time of lib element or FF's?

Regards,
Dr.farnsworth

Dude,

Setup and Hold times have not relations with each other.It is the property of the FFs in the libs. Check below

The only relation between hold time and setup time is:
th(hold) + ts(setup) >= 0,
this is a very important concept, especially when you meet the negative value of hold time.

Sincerely,
Jarod

provided your clock period > hold time + setup time, there should be no problem.

if hold time = 3ns, setup time = 1ns (hold > setup time), and your clock period = 10ns

so, hold time means, ur signal should arrive aft 3 ns, setup time means your signal should arrive before (10 - 1) = 9 ns,

thus ur signal should arrive in x ns, where 3 < x < 9.

jeet_asic

Points: 2