Hi Al,
Sorry for the delay in responding. Thanks for the additional information


On 15/09/16 1:57 AM, al davis wrote:
There is another hidden issue here, something I have been working on. As originally stated, rise=fall=delay=0, there is nothing in the circuit to hint at what time stepping to start with, so the automated step control would miss the oscillation. In the original, the requested step of 1ps was a hint, but otherwise with what Felix suggested, it would have skipped by the oscillation. You might call this a "bug" but most other simulators are worse. By giving a finite rise time, the simulator now has some basis to figure out time stepping and can go from there. You just need something, somewhere, that somehow requests a step size less then the expected period of the oscillator.
ngspice behaves differently with the statement VCC 10 0 PULSE(0 8), it uses the step time by default when not explicitly specified.

1ps is a very small time step for a 100MHz oscillator. I am injecting a current pulse into the oscillator and measuring the phase shift in the signal. I need to measure down to 0.01 radians. I was experimenting with ngspice with different step times but the phase shifts I was observing were not sensible.

Now I have a better understanding on how to use GNUCap I can repeat the experiments using it.

Richard.

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