Artifacts in Swept Frequency Plot

I am trying to simulate an LC band pass filter. I sometimes get ‘artifacts’ in the output plot. Any thoughts…is this due to floating point precision ? See below:


A connection to ground (GND or 0) is missing.

Each circuit has to have a ground node (gnd or 0)!

See ngspice manual chapter 2.1.3.5.

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Thanks for the reply holger. That solved the issue. I had erroneously thought that since this type of measurement is a relative voltage (output/input) and not absolute voltage (wrt ground), a ground /zero reference was not required.

I marked holgers answer as the solution. Please make a habit out of this for each of your threads that has a clear solution. It helps others searching this forum to find answers quicker.

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