Re: [Help-gnucap] Oscillator Simulation

[Richard Gipps]

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.