Clock Skew

Clock Skew 

    Que:Explain clock skew and write detail about positive and negative clock skew.

 ANS:

• Clock skew means clock riching to flip-flop at different time.
• Differance between arrival time of the clock at different devices.

        skew=max|t1-t2| 

• There are two types of clock skew: Positive skew & Negative skew

 

Positive Skew:

 

• When both data and clock are traveling in same direction it is called positive skew.
  

• The routing direction decides whether the clock skew is positive or negative.
  

• If clock at the capture flip-flop takes more time to reach as compared to the clock at the launch flip-flop refer it as positive clock skew. 

 

 

 Negative Skew: 

• When both data and clock are traveling in opposite direction it is called negative skew.
  

• If clock at the capture flip-flop takes less time to reach at the launch flip-flop referred to as negative clock skew. 

 

To Minimize the effect of clock skew: 

• In order to control the clock skew the clock distribution techniques are used.
  

• The main problem in clock distribution is the availability of capacitance which plays important role in clocked system so, avoid this problem using clock distribution.     

 

 Sources of clock skew: 

• If they are from external sources they may arrive skewed.
  

• The delays though the clock network may vary with position on the chip.
  

• Skew can vary with temperature due to temperature dependencies on gate/buffer delay and wire delay.