How to setup HSPICE option to smooth the rising/falling edge in transient noise

[tim82518]

Hi

I'm doing a transient noise simulation to calculate jitter of PLL
Here I have a setup question
As figure shown below, blow line is reference clock, red one is PLL's output.
I'm curious why the waveform is not very smooth. What option can be given to make it smooth?
Furthermore, does this kind of unsmooth waveform worsen the jitter calculation?
I list all the setup I have given and version of HSPICE for your reference. Thanks!

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HSPICE -- H-2013.03-SP2
 
.option                                
.OPTIONS POST ACCURATE METHOD=GEAR 
+ runlvl = 6
+ measform=3 MEASFILE=1 post   
+probe=1 
 
.TRANNOISE v(CKOUT) 
+ METHOD=MC
+ SAMPLES=1 
+ SEED=2 
+ FMAX=0.4G

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