differential osciillator problem

[aliqureshi436]

Hi i am trying to design the differential ring oscillator at 3 GHz, pic is attached. So far what i have been able to do is to make it oscillate when the simulation time is 20nsecs, but whenever i increase simulation time the oscillator starts giving dc!
The other problem is that i have not been able to find widths for the pmos and nmos, i have tried almost every width (parametric analysis) but the circuit only oscillates at 1 specific relation of widths and i don't know weather there is a particular relation to find width or only way is hit and try!
Please help.

 

[ppat2006]

u plz give me a clear diagram with all the width , length and bias values since i m trying to build the same diff ring oscillator in mentor graphics daic tool and matlab/simulink. then i will chk and try to build your ckt

even i face the same problem it shows square wave only when i put inverters at the + and - output otherwise it dont shows any oscillation