How to plot tuning rangevs frequency in spectre

Hi,

I have a question in spectre, How to plot the tuning range vs amplitude of the output signal for a ring oscillator. Also I want to plot tuning range voltage vs frequency for an oscillator.

I have attached a figure which I got from one of the spectre lab manual from internet. But I dont know how he acheived it. Please let me know.

Thanks in advance.

Regards,
Prakash.