osc frequency changed in simulation !!!

[mustangyhz]

osc frequency

I designed a negative resistor LC oscillator, for the first time, I simulated it in spectre, it's frequency was about 2.5GHz, without changing any thing, I simulated it for the second time, it's frequency changed to about 5GHz! why! Anybody met this thing?

 

[Blackuni]

Re: osc frequency changed!!!

Hi,

technically it should not be changing. do u have both run results/log files???

if u do we can get some clue as wht made it to happen...

what abt initlal condition/ operating point for both run?? are they same??

try doing monte carlo run by distributing u r device parameter to check wthr any 1 value gives u r first results.

By the way whtz the freq u r osc. designed for???

Thanks,

 

[mustangyhz]

Re: osc frequency changed!!!

The freq of my osc is 2.4GHz. Initlal condition was the same ipulse(current1 200uA, current2 0uA, raise time 1ns)! For the majority of the time, the frequecy is about 5GHz, some time ,it is 2.5 GHz. Now, I can not get the 2.5GHz output
thanks!

 

[Blackuni]

Re: osc frequency changed!!!

Hi,

can u share u r schematic/netlist?? I try to find wht wnt wrong.

Thanks,

 

[lvlei0309]

osc frequency changed!!!

if u use pss run the simulation it is possible.
pss sometime is not correct. i guess it is 5GHz. At some case, pss take two cycles as one , so cause 2.5GHz.

 

[leo_o2]

osc frequency changed!!!

Any difference for model?

 

[AdvaRes]

Re: osc frequency changed!!!

Hi,

technically it should not be changing. do u have both run results/log files???

if u do we can get some clue as wht made it to happen...

what abt initlal condition/ operating point for both run?? are they same??

try doing monte carlo run by distributing u r device parameter to check wthr any 1 value gives u r first results.

By the way whtz the freq u r osc. designed for???

Thanks,

Hi all,
Could someone tell me what monte Carlo run is used for ?

 

[Blackuni]

Re: osc frequency changed!!!

Hi,

monte carlo analysis is the beginners level Yield analysis.

to put it simple with an example

threshold voltage is a parameter which affects u r ckts performance.
and it varies across the wafer, In spice u can model this variation into any of the random distribution.

So spice will vary the threshold voltage(foundry will provide the distribution model and the level of variation) according to the distribution do multiple simulation.

this will help u make sure u r ckt works in most of the cases.

hope its clear.

Thanks,

 

[psmon]

osc frequency changed!!!

Is your waveform sine wave?

 

[mustangyhz]

osc frequency changed!!!

I update ic5141_base to user610, change the pdk and select mmsim610, the problem is solved.
Thanks!!!