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   Circuit simulators software

• #10: pyCircuit I am starting off with a fairly recent contribution to the world of simulators. PyCircuit is a package available from a git repository and it has been partly developed by a friend of mine, Joacim Frisk. The package allows symbolic analysis and it covers the AC, DC, transient analyses as well as say PSS and PAC. It has an embryo for a gnucap (see #7) interface, i.e., it can read a gnucap netlist and run the simulations on it.
  I just want you to get some flavour on what’s going on out there… and the rest of the list is probably more known to you. I have only done some rudimentary trials with pycircuit.
  
• #9: TINA-TI I continue the list with a tool I have never used … and once again I might not do TI (Texas Instruments) justice by putting their Spice simulator for windows last. However, it is for windows only and they do not provide the whole TINA-TI package for free. It supports AC, Transient, DC analysis, some Fourier analyses and a couple of steady-state analyses. If I get some time, I will evaluate the tool more (I just need a windows machine … or at least try over wine). As #5 does, they offer a large variety of free circuit descriptions to be downloaded from their home page.
  
• #8: QUCS The quite universal circuit simulator (QUCS) is also a freeware and it is very fast to setup simulation and start crunching those numbers. Due to its GUI it is quite “educational” and a bit PCB-oriented. It has the basic simulator options and can handle veriloga code (and more). As we talk about the GUI, the cells are stored in an XML format and we once started to work on an XML parser to be able to port schematics/netlists between different tools … that is yet to happen.
  
• #7: Gnucap Gnucap is also free, but requires some hands-on to operate and to “get into”. This hurdle and the fact that it is not that well maintained currently (or?) puts this after bullet #6. I put it high on the list, though, as it is associated with the gEda flow and is available in e.g. the ubuntu standard repositories. It does not have any “advanced” simulator options and we are “limited” to DC, AC, transient analyses (for now…) It enables us to do mixed-mode simulations.
  
• #6: Ngspice I like ngspice! It is also free and fairly well maintained. It enables me to quite quickly go from a spice-format and run with a free simulator. Quite easily, I can kick of a large corner set using an unlimited amount of licenses. As for the other free simulators, it is a bit limited in terms of simulation options (does not contain periodic steady-state analyses, etc.). At home I use it quite extensively to test different ideas and it can be trimmed to simulate veriloga, etc. It handles BSIM4 and EKV models.
  
• #5: LTSpice Linear Technologies actually enables us to use their spice simulator for free! Further on, it can be quite easily associated with the Electric layout editor and some of the other freeware tools such as the gEda package. In addition, Linear also provide a huge list of example circuits to download from their home page. LTSpice handles “all” transistor models.
  
• #4: Pspice Cadence acquired the Pspice tool which was originally developed by Microsim. Unfortunately it is available on windows only but it is quite handy to work with as such. Now, professionally, I tend to have access to #1 and #2 on this list and therefore I do not really use #3 and #4 anymore.
  
• #3: Hspice Synopsys acquired the Hspice simulator from Meta Software quite a few years ago. (I still have a Meta Software manual…) and it was also the first simulator that I used “professionally”. Back in those days we used the Led layout editor from which we generated the netlist, handhacked the bulk connections, hand hacked the testbenches, etc. We were quite immature and today I would have done it a lot differently…
  
• #2: Eldo Eldo from Mentor Graphics takes a strong position and definitely competes with #1… As I joined Sicon Semiconductor I left the cadence-dominated world and got to work with eldo. It was a pleasant experience and I also enjoyed the script-based environment (kind of anti-gui) that we worked with. Yes, not really related to the simulator, but yet … I found that, at least some years ago, eldo had a much more robust way of going towards mixed-mode simulations. It could probably be due to the fact that in the netlist environment, it was easier to handle this than through the schematic/GUI of #1 on the list.
  
• #1: Spectre Cadence is on the top again. Actually, I would probably put eldo here if it was not for a strange simulation error I got in one of my extracted cells some years ago. Unfortunately, we had to push out the tape-out due to this. I am still today not sure what went wrong… The two competitors for the top place are eldo and spectre. Since I mainly use spectre nowadays it ends up here. The simulator also gets credit for Ken Kundert’s work and his designer’s guide web page. Spectre also ends up high on the list now, as they have added transient noise, and dynamic sweeps to their portfolio…