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"Ringing" on the HB time domain waveforms

Question asked by EMIKA on Mar 29, 2006
I am designing a Class E circuit, using a pHEMT device modelled with TOM3. At the output I have presented the required shunt capacitance and load network for Class E operation. The output expected is at the third harmonic (ie. the output filter is tuned to the third harmonic). The fundamental frequency is 1GHz. When I simulate this circuit in HB, then I obtain the correct voltage and current time domain output waveforms at the output of the device.
However, as soon as I include some inductance to represent bondwires (approx. 0.5 nH), the time domain waveforms display a lot of 'ringing' on them - in fact it is so bad that it almost looks like high amplitude noise. As I decrease the inductance, the original waveforms are gradually recovered.

I don't understand what is going on, as 0.5 nH at 1GHz should not make that much of a difference. What does it mean in HB simulation, when the time domain waveforms display sudden 'ringing' (almost oscillating) behaviour? Am I right in saying that HB cannot display oscillation so this phenomenon cannot be oscillation?