How negative Skew effects frequency

[kunal1514]

Hi All,

Can any body tell me How negative skew effects frequency

 

[shelkerahul]

Negative skew means, clock is reaching capture flop is faster than the launch. So you have small timing window to meet the timing. In other words possibility of setup violation will increase, so ultimately your frequency will reduce….

Hope explanation is clear enough….

 

[nikhilindia85]

i think due to the negative skew clk freq increases.
tclk>tc-q+tcomb+tsetup+tskew (for negative skew)
tclk>tc-q+tcomb+tsetup-tskew (for possitive skew)

 

[megastar007]

What shelkerahul said is correct

 

[alam.tauqueer]

yes thats a correct and good answer...

 

[kunal1514]

Shelkerahul

Has written

Negative skew means, clock is reaching capture flop is faster than the launch. So you have small timing window to meet the timing. In other words possibility of setup violation will increase, so ultimately your frequency will reduce….

Hope explanation is clear enough….

Can u explain this thru some equation i will be thankful to u.

 

[shelkerahul]

I have never used any equation for STA. so I cannot put explanations in equation properly. I will try to put some rough equation

Required time = clock cycle + skew – setup time of a flop

Setup violations = required time – arrival time

So if your skew is negative, required time will be less, so probability of violating setup is more. More the violation lower the frequency of a circuit.

What I personally feel, don’t go with equation, equation will always confuse you ( I get confuse with equation :wink: ). Get a feel of STA. it will be better.