Colpitts simulation results differ from LtSpice

I simulated a Colpitts oscilator in LtSpice. The oscillator does initially start up but stop after a while. I copied the netlist into QSpice and with QSpice it continues to operate. Does anyone have clue to explain the difference?

Hi, corvenner.

I suspect that it would help to post the circuit.


Thank you for the response.You are right, but the forum allowed me only to insert one object. I have created a ZIP. But I’m also not allowed to upload this. The LTspice design contains a auto generated symbol. So I was really astound that dropping the netlist into QSpice gave me a running design.

Any ideas of how to accomplish this?

I expect that everything is in here. It might be necessary to modify some references.

I ran your LTspice file but got an oscillation. Did you change anything in Simulate > Control Panel > SPICE ? (I Reset to Default Values for this test). LTspice and Qspice may have different simulation option (compare .option) which can introduce different.

For QSpice, if you add .options method=gear, it can eliminate oscillation in your circuit. However, Mike’s gave a warning about using Gear method, refer to this post for reference.
Apparent Kirchhoff’s law violation - QSPICE - Qorvo Tech Forum

Thank you for your response. I made indeed a small change in the circuit. In the first post there was a voltage source that I have used for an ac analysis. This source was open and I got a warning. For this I removed it. When I run the simulation again it stopped after about 450us although it should run until 500us.

When I look at the results that you attained I expect that the oscillation stops and start when you zoom in at the location where the wave is far from smooth.

I can’t notice this from the QSpice simulation.

The error log of LtSpice gives me something to:

Heightened Def Con from 0.00049858 to 0.0004986
Heightened Def Con from 0.000498706 to 0.000498726
Heightened Def Con from 0.000498807 to 0.000498827
Heightened Def Con from 0.000498912 to 0.000498932
Heightened Def Con from 0.000499038 to 0.000499058

It seems that it has problems to get a stabil dc operating point.