lc oscillator hspice tran time

Dear all,

I am using tsmc 0.13um to design one differential LC-VCO oscillator. I am using HSpice to simulate the .tran. The transistor uses the model provided by tsmc. The other components using ideal model, for example: L, C, R. I have set the trasisent step small enough. Moreover, I have add the starup pulse for the VCO to start up the oscillation.

However, the oscillator does not oscillate. How could I solve it? Even it can start up at first time, it will dampling out finially. Even I increase the size of the cross coupled transistor size or current source. It could not oscillate continuously. How could I solve it?

thanks

wccheng

The transient step size must be set really small. Otherwise it indroduces a loss which cam case a high-Q circuit to not oscillate in spice. You may need to do some trial & error. As a srarting point use a step size of 1/1000 of the period.

also maybe your gm is not big enough

hi,have u got the information about LC-VCO, if u got it please send me.........