Spectre Transient setting !!!!!!!!

Hi all,

I have a question about transient setting for 5GHz VCO sim.

When I run the transient sim over the VCO with 20nS stop time, the sim result shows the VCO does start to oscillate to 2Vpp.

But when I extend the stop time to 50nS, the sim result shows that the start up fails.

Does anyone know how to solve the problem?

My current setting is reltol/vsbstol/iabstol=1e-5/3e-8/1e-12,gear2only, no accuracy defaults is checked


Thanks

What program do you work with? Spectre?

There are better alternatives than transient simulation. Some programs (like ansoft designer) use assisted harmonic balance. They look for the oscillation frequency first and then perform harmonic balance simulation on this frequency. This algorithms is a lot more solid than simulating in transient and performing fft to detect oscillation frequency.

ADS does this too. And RF design environment is a cooperation of spectre and ADS.