Clock Uncertainity- max operating freq, max freq calculation

[vlsi_freak]

Clock Uncertainity

Hello All,

Consider a FF1-Comb-FF2 circuit, both flops clocked by same clock clk1.
If clock frequency of clk1 is 16 ns, Comb delay is 0 ns, FF set up time is 0.2 ns and Clock uncertainity is 0.5 ns,

1. What will be max operating freq of this system. ?
2. Will clock unceratainity be used in max freq calculation ?

Plz share your thoughts,

regards,
freak

 

[zhongminchen]

Re: Clock Uncertainity

Theriotically, the maximal frequency is (1/0.7)GHz
clock uncertainly always be used to estimate the clock skew or jitter or reserved margin
usually, circuit highest frequency is determined by the critical path...

 

[vlsi_freak]

Re: Clock Uncertainity

Hi zhong

How u got 0.7 ?

regards,
freak

 

[ljxpjpjljx]

Re: Clock Uncertainity

may be do simulation will be better to estimate the value!

 

[vlsi_freak]

Re: Clock Uncertainity

Hi ljxpjpjljx,

By simulation i think we cannot find this. Simulation is used only for functional check.

regards,
freak

 

[visualart]

Clock Uncertainity

you may get the maxum frequency by the fellow express:
max freq = 1/(16+0.2+0.5+T(clk to Q))

 

[edagops]

Re: Clock Uncertainity

You can get max freq using below calc.

max freq = 1/ (clk-q delay of FF2 + combo delay(FF1-FF2) + setup req of FF2 + clock skew(b/w launch FF1 and capture FF2 clk path) + clk uncertainty (jitter)

while calulating max freq, you should consider all the above factors including clock uncertainty

Added after 30 minutes:

PS : clk-q delay correspond to FF1 not FF2

max freq = 1/ (clk-q delay of FF1 + combo delay(FF1-FF2) + setup req of FF2 + clock skew(b/w launch FF1 and capture FF2 clk path) + clk uncertainty (jitter)

 

[raki31]

Re: Clock Uncertainity

So

max freq = 1/( 0{clk-q of FF1} + 0{delay of comb} + 0.2{setup of FF2} + 0 {skew} + 0.5 {uncertainity} )

==> 1/(0.7ns)
==> 1.428 Ghz................right??