[jitter-timing] Rise & Fall Times - Part 2
- From: "JitLab" <jitlab@xxxxxxxxxxx>
- To: <jitter-timing@xxxxxxxxxxxxx>
- Date: Sat, 20 Sep 2003 14:32:29 -0600
Rise & Fall Times - Part 2
Significance of Rise Time & Fall Time:
This is best explained by comparing a square wave with a triangular wave. In
an ideal square wave with 50% duty cycle, the rise time will be 0 and the
signal will be above threshold for 100% of the half period time. In a
symmetric triangular wave, this is reduced to just 50%. More severely
affected is the total area above the threshold, which is reduced to 25% of
that of square wave's. Though the information about loss of time above
threshold is conveyed by many other parameters, the information about loss
of area above threshold is only conveyed by rise and fall times.
Rise Time & Fall Time Requirements:
The rise time & fall time should be small compared to the clock period. A
factor of 10 is considered good. Very large rise or fall times have the risk
of the cycles going undetected. Also, large rise or fall times mean that the
signal will be hovering around mid level for too long, making the system
highly susceptible to noise and multiple triggering if there is not enough
hysteresis.
This might make you think that the faster rise & fall times are, the better
the system is. Not really. Very fast rise or fall times are not free from
trouble. They might cause severe ringing at the receiver resulting in
reduction in voltage & timing margins or even double triggering. Or the fast
edges can & will get coupled to the adjacent signal lines causing false
triggering on them or reducing the voltage margins. For more info, visit
http://www.aubraux.com/free-jitter-software.php
Other related posts:
- » [jitter-timing] Rise & Fall Times - Part 2
