contamintion delay and hold time

[yuvalkesi]

Hi all,
I'm trying to figure out the relation between Thold and Tcd (hold time & contamination delay) and I'm really confused here.
For example, I read in alot of books that Thold(FF2) <= Tcd(FF1) + Tcd(logic) (the regular example usually shown).
What I don't understand is this: Let's say Thold IS less than Tcd, but in the follwoing example herein, the signal went to '0' after Tcd (=min. prop. delay) , and even though Thold is shorter than Tcd (so the 'rule' applies), the hold time condition was not met because the signal should be stable for hold time of FF2, and it was not... so I'm confused, and obviuosly I got it wrong...
any help?
Thanks!

 

[aruipksni]

Hi all,
I'm trying to figure out the relation between Thold and Tcd (hold time & contamination delay) and I'm really confused here.
For example, I read in alot of books that Thold(FF2) <= Tcd(FF1) + Tcd(logic) (the regular example usually shown).
What I don't understand is this: Let's say Thold IS less than Tcd, but in the follwoing example herein, the signal went to '0' after Tcd (=min. prop. delay) , and even though Thold is shorter than Tcd (so the 'rule' applies), the hold time condition was not met because the signal should be stable for hold time of FF2, and it was not... so I'm confused, and obviuosly I got it wrong...
any help?
Thanks!

you assuming to ff chaned together with some logic bewteen :