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Help needed to design LC VCO running @2.45GHz

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xwing

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I'm a beginner trying to design a simple cross coupled LC VCO using mos varactors. I can't seem to oscillate the model even changing several of the parameters.

Problems
1) I have encountered is the transient simulation using Cadence gives weird results; I can get some waveforms for say 20ns simulation but extending it to 1u will not give me any oscillation at all.

2) The attached file shows my schematic and waveform. The puzzling think is the output swings +/- 8volts even though my supply is set at 1.8volt. My values for the two nmos are W=100u L=.18u. Finger of 10. The supply current is set at 30mA
(i noe it will cause a breakdown but lower current supply will not give any oscillation.

Really puzzled and confused. Can anyone helped??
 

Regarding simulation problem, when you extend the stop time to 1u force a small time step to the simulator (the same you used previously).

I hope it can help.
Mazz
 

Mazz said:
Regarding simulation problem, when you extend the stop time to 1u force a small time step to the simulator (the same you used previously).

I hope it can help.
Mazz
Click to expand...
Or; you should change size and max size of samples in tran options if you want simulation 1us.

Added after 6 minutes:

xwing said:
2) The attached file shows my schematic and waveform. The puzzling think is the output swings +/- 8volts even though my supply is set at 1.8volt. My values for the two nmos are W=100u L=.18u. Finger of 10. The supply current is set at 30mA
(i noe it will cause a breakdown but lower current supply will not give any oscillation.
Click to expand...
Put a resistor between inductance and vdd.
 

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