Oscillator simulation with BJT

[GGAPBE96]

bjt oscillator

What is the best BJT model to simulate oscillators? Now I use Gummel Poon model,but the result is bad...

 

[E-design]

oscillator bjt

Give more information. What results are bad?

 

[GGAPBE96]

Thanks E-design,

The harmonic spectrum isn't coinsident with measurement at all.
The magnitude of 1st harmonic,simulation result is -80dBm but measurement is -40dBm.

 

[E-design]

What program are you using? Can you post your circuit?

 

[GGAPBE96]

I can't post the circuit...
I use Agilent ADS. The circuit is 300MHz VCO. Inductors and varicap are SPICE models and transistor is Gummel Poon model.

This problem (harmonics mismatch between simulation and measurement) often arises when I simulate oscillators.

 

[E-design]

Try and verify the accuracy of your model by extracting parameters yourself and compare with published parameters. I have done many osc designs with ADS and the measured results most of the time agrees closely with the simulated results provided the model is accurate. You should also try and verify with another simulator. I often use Ansoft Designer to do this.

 

[GGAPBE96]

Thank you E-design,
I'll try to extract device parameters.