Anybody used "eye diagram" function in Cadence spe

eye diagram functions

Hi, I have to use the eye-diagram special function in spectre. However, I do not understand the meaning of "period" in the option card. Please help me.

Thanks in advance!

eye diagram simulation

I have read once about this measurement. 1st u need to use vpwl source or stimulus file to create a fix pulse width random input data pattern. then only u use the eyediagram function. period is the period of the signal u wan to overlay on the "eye" waveform, i.e. the random input pattern.

eye diagram cadence

Period is the 'time period' of the signal that you are plotting the eye for. (or 1/frequency).

Usually eye-diagrams are used to determine the jitter on the signal that has a constant frequency but with some associated jitter.

eyediagram defination cadence

Hi,guys:
Thanks for ur reply!
I still have a silly question, how long should I choose for the period?For example, there is a periodic signal with a bit-rate of 622Mbps. so how long should I set for the period of eye-diagram, 3.2ns or something else?

with regards!

cadence eyediagram function

Hi Scuhai,

Since your data rate is 622Mbps, then your period will be 1/R(data rate). So, it will be 1.60ns. In the PRBS generator which u can get from ahdl library, under the "tperiod" option, you have to put the value of 1.60ns. Now after you are running the simulation, when you want to view the eyediagram of any node, you click "VT" in calculator from spectre, then point on the net and the select the eye-diagram option. Then you will get the command box asking for start time, stop time and period. So, let say you are running for 1us, then let say you put start at 800ns and stop at 900ns, the "period" you put now is to see how many bits you want to overlap in order to find the jitter. let say you want to see the eyediagram for 10 bit, then you have to put the period as 10 x 1.60ns = 16ns. The point here is each period will have the time for one bit.

Hope this helps you.

Regards,
Suria3

cadence eyedigram

I have the following question regarding jitter:

In the case of a VCO (which is my case) the jitter changes dramaticaly according to the start-stop period defined in the function. So which is the appropriate start-stop time in order to derive the correct value of the jiiter?

Thanks