gEDA-user: TwoStageAmp example

[Dan McMahill]

al davis wrote:

>> Rather, Gnucap should do a check before 
>> running an analysis to verify that the operating point has
>> already been computed and is known.  If it's unknown, then
>> Gnucap should print out a warning like "No operating point --
>> you probably need to run op".
> 
> That would be an improvement, but the power off test is a valid 
> test, and you don't need to do it for a linear circuit.
> 
> It probably should print a warning whenever "ac" is done after 
> anything other that "op", because only after an "op" will it 
> give the same answers as Spice.  If you do "ac" after "tran" it 
> will use the last step of the "tran" as the operating point.  
> This is extremely valuable if you are doing real analog work.  
> I really need to write up that Class-B amplifier example to 
> show it.

I have to agree 100% with Al here.  The ability to easily run the ac 
analysis at whatever operating point you have, be it from an explicit 
operating point analysis or where a transient stopped, is extremely 
important.  Al's class-B amp is a good example because of course the 
output devices undergo very large signal changes and you should be 
concerned with small signal stability over the entire output range. 
Other circuits may not have a d.c. operating point that means anything.

> Probably, it should always print a note:  "using operating point 
> xxxxxxx".

that would be useful.

-Dan