Oscillator rise/fall time

hi all,

i want to know what's the reasonable rise & fall time for a normal oscillator working at around 200MHz to 300MHz? the oscillator may not need to be a state of the art one; just a normal one can do the work


thank you!
c.m.

10% of the one period should be OK.

chang830 said:

10% of the one period should be OK.

Click to expand...

so long? then 5n peirod will have rise time 0.5n and fall time 0.5n?

currentmirror2000 said:

chang830 said:

10% of the one period should be OK.

Click to expand...

so long? then 5n peirod will have rise time 0.5n and fall time 0.5n?

Click to expand...

Rise/fall time will be determined by the drive capability of the oscillator output stage and the load capacitor. Its requirement will depend on the applications.

Also, hope below helps.

***********************
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.

*******************************************