On Monday 17 September 2007, Dan McMahill wrote: > I'd comment, but I probably can't give a good measure of the > learning curve. From my perspective, if you've used any > circuit simulators, ngspice and gnucap are both pretty easy. > But then again I first used spice nearly 2 decades ago and > use circuit simulators daily so most of my learning curve > memory is pretty distant. gnucap has some neat capabilities > like being able to directly get at some internal components > of device models (junction current vs charging current in a > diode for example). gnucap also is quite a bit better than > ng-spice for mixed mode sims since it was designed for that. > I can't recall though if gnucap has small signal noise > analysis at the moment.
No. no small signal noise analysis. Use NG-spice for that. There is also no small signal distortion analysis. Again, use NG-spice for that. On the other hand, I have never found the small signal distortion analysis to be very useful, because it doesn't show large signal distortion at all. What I have found more useful is a real Fourier analysis. For this, gnucap wins. The Fourier analysis and time stepping work together to significantly lower the noise, so it is actually useful for measuring distortion. Gnucap is a lot faster for large circuits. I have one that runs in 8 hours in NG-spice, 40 seconds in gnucap. Quadratic time vs. linear time. As to the learning curve, it depends on where you are coming from. gnucap interactive commands are different from spice. As a teacher, I found that I could get students started faster on gnucap than any other, even the graphic ones. If you are starting cold, the command line is really the easiest way! The biggest trip point is the sequencing of attaching probes and doing an analysis. Batch spice doesn't care about sequencing. As a result, it doesn't let you play. Gnucap cares completely about sequencing. You need to attach the probes before you turn the power on (run the analysis), like you would with a GUI, or a real circuit. Gnucap is more like a breadboard metaphor. Spice is more like a "declarative programming language" metaphor. > I'm a fan of learning about netlists and doing the first > couple of sims by typing in a netlist by hand. Why? Because > even with expensive commercial CAD systems, problems come up > where you have to dig into the netlist to debug. Besides, > it's one less thing to worry about when you're getting > started. That's another thing I ran into in teaching. Other profs would teach only with a GUI, so they might not see a netlist ever, or until they hit a course I was teaching. I start them with a netlist, then let them learn a GUI later if they want to. With Spice, you need to make a file containing the netlist. Gnucap lets you type it in interactively, then make many cycles of change and simulate again, interactively. With Spice, every change and simulate again is another edit of a file. Too often, students are taught simulation as an afterthought. You do everything else, including actually build one, then simulate to appease the professor. They don't learn that a big reason for simulation is that it is easier than the many rebuild cycles on a real circuit. They also don't learn that simulation can give you data you can't measure, and can directly give you the numbers you want, as opposed to measuring what you can measure and calculating from there. gnucap is better in this respect, because lots more "probes" are available. You can directly probe things like the charge in a capacitor, the incremental capacitance of a junction, the transconductance of a transistor. The biggest problem I ran into is that many students can only use a GUI. They can't even type "ls" to get a file listing. For them any command line is incredibly confusing. They need a few weeks of lessons in how to use a real computer first. Many profs respond to this by only using a GUI, which at best only delays the awakening, at worst they never learn. If you are just starting with gnucap, get the stable release (0.35). When you have a need for something it doesn't do, the development version might do it. There is a big difference between the latest stable version and the latest development version. If you want to help us make a Free simulator that competes against the big bucks simulators, get the development version and dive in. _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user