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help with transient analysis of a vco in cadence

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hi. i am working on designing in schematic of cadence a vco at 77GHz (13ps the period of the signal). The problem is that when i use transient analysis, i see the circuit oscillating and working fine only if the simulation time is equal to or lower than 1 nanosec. If the simulation time is larger than 1ns, the circuit doesn't seem to oscillate at all!!! This is paradox! Has this problem occured to anyone? help please!

Thanks
 

use parameter "max step" to define maximum simulation step (e.g. max step = Tosc_period/10), and "trap" method of integration
 
what is your simulator? what are your tolerance settings? did you set an initial condition to start oscillation?
 

thank you!!! It worked!!! the trap method of integration was the key....thank you a lot
(Initial conditions not needed...it amplifies the noise of the circuit...)
 

simulator - spectre;
tolerance can depends on work station power also, it should be adjusted to your target;
IC isn't necessary, but typically use Vdd on pulse
 

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