I used to be almost as sim-averse as Pease, who is shown lining birdcages with printouts and hurling machines from rooftops.īut then my tech showed me how a colleague's filter banks all oscillated (and it wasn't obvious from inspection, as they were Friend-Delyannis topologies and a bitch to design). You can make stuff now where the first cut actually fits together. I really love computers for PCB and mechanical design. :?: Perhaps I'm just showing some old dinosaur butt. But then there's the short list that never made sense. It always made sense after you figured out what was what. Now maybe I was a little off sheet wrt to the devices typical applications but welcome to my world. Of course it only shows up in production because the working prototype allocated the transistors differently. While a better sim may include the intrinsic substrate diode, I've seen really obscure things like interactions between adjacent devices from heavy current in one transistor affecting the one next to it in strange ways. My trouble with circuit sims is I was always running into subtle component quirks like with the good old cheap 3086 transistor array. I used the tab function to print crude frequency response plots on an old dot matrix printer, but I'm wandering off topic. I did write some crude software to help me design oddball multi-pole cascaded filter sections back in the bad old days ('70s) having to design anti-alias, anti-imaging, and reconstruction filters around BBD and CCD delay lines (with HF pre-/de-emphasis included). I never really got comfortable with circuit simulations, it seemed like there was a catch 22 where you had to know what you didn't know to program the simulation to account for what you didn't know.? How's that for circular mumbo jumbo logic? ![]() ![]() OTOH the simulator will generally not reveal the trip-point-vicinity oscillations unless you add parasitics to the model. ![]() The reality on the breadboard is usually quite stable and benign by comparison. One caveat for those using simulators and not getting to the bench very often: the application of a bit of positive feedback to these parts, to reduce or elminate chatter at thresholds, throws Spice in my version at least into fits.
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