If I simulate it with Electronics Workbench it happily oscillates.
With PSpice it doesn't, no matter how I change the feedback.
I suspect that some noise source should be added to trigger the
oscillation, but
don't know how, nor I am sure that this is indeed true.
Any help is gratefully accepted, thanks.
73 Alberto I2PHD
Dear Alberto, LF group,
Try connecting a pulsed voltage source (VPULSE) in series with the tank
circuit - set it to generate a pulse width of, say, 1/2 a cycle of the
expected oscillator frequency, starting at t=0. The pulse will cause the
tank circuit to "ring", and the oscillations should build up from there.
Once the pulse has finished, the source just behaves as a short circuit .
You will want to play with the amplitude of the pulse so that the ringing
has roughly similar amplitude to the steady-state oscillator level,
otherwise it will take a long time to settle. In any case, the simulation
must run for a large number of oscillator cycles in order for the circuit
to reach equilibrium - this is also true of a real oscillator! You may also
find it necessary to set the transient simulation "step ceiling" to a value
that is a small fraction of a cycle, otherwise peculiar waveforms will
result, because the default time step size selected by PSpice is normally
too big for a high Q circuit.
Cheers, Jim Moritz
73 de M0BMU
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