Set Noise Type to timedomain, enter a large number for Noise Skip Count (or 0 for Number of Points), select Add Specific Points and enter the value of t_c there.

t_c is the time where you want to measure the jitter, usually the time where the signal crosses the theshold level of the following stage. You have to find t_c by performing a PSS analysis. Then you activate the Pnoise analysis for the following simulation run, while leaving all parameters of the PSS analysis unchanged (so that t_c will not change).

Select tdnoise, Integ Output Noise, Total Noise and Magnitude. Set Start Frequency to 0 and Stop Frequency to f₀/2, where f₀ is the frequency of your PSS analysis. The result will be the square root of equation (55), which you only have to divide by dv(t_c)/dt according to equation (54) in order to obtain the jitter.

Your sweep range in the Pnoise analysis should also be from 0 (or a very low frequency) to f₀/2. If you have 1/f noise in your devices, you should probably use a logarithmic sweep where a lower limit of 0 is not possible.

Regarding the timeindex: If you entered a large value for Noise Skip Count, you should have for timeindex the values 0 (which you can ignore) and t_c (which you entered in Add Specific Points). In this case, you should of course use timeindex=t_c.

If you entered 0 for Number of Points, you will only have timeindex=0, which is really timeindex=t_c. Any additional points you might have entered will also have a timeindex value that is too low by t_c (if t_c is the lowest value you entered). This is a bug in SpectreRF that I reported to Cadence some time ago in SR 32827714, it is now handled as PCR 740140.

The result is the jitter of the output signal that you have specified in your Pnoise analysis. This must of course also be the signal that you use to determine t_c and dv(t_c)/dt.

This simulation gives you the jitter caused by the intrinsic noise of your devices. In practice, you will generally also have other effects that will cause jitter, like for example disturbances on the power supplies or intersymbol interference due to limited bandwidth for data signals.

A DLL by itself is not an autonomous system, so I do not think that the analysis in section 10 of http://www.designers-guide.com/Analysis/PLLnoise+jitter.pdf applies here. However, the input signal to the DLL might come from a VCO that exhibits accumulating jitter.

Of course, the jitter will generally increase over the length of the delay chain, as described for the case of the ripple counter at the top of page 28. However, this "jitter accumulation" is fundamentally different from the accumulating jitter in an autonomous system like a VCO.

Hello, I use the method with noise type time domain but when I see the results I have the noise in V^2/Hz but for jitter I need to have dBc/Hz.

Thanks for your explication

I am ok but in the equation (54)

J=squart(var...)/dv/dt the unit are not good for me.

Because J is second

the unit of dv/dt is Volt/second and Squart(...) is V.s^(1/2)

thus J is in s^(3/2)
i thimk