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Electronics Forum / CAD / October 2007Anyone know what Circut Bob Pease was going on about?
From: An EDN Blog post about Analog Design tools. http://www.edn.com/blog/1480000148/post/240014624.html Bob Pease at a Panel session on DFM went on about a circuit Spice said couldn't work and held a breadboard up with the circuit he said was in production. Anyone know what it was? Robert H. >From: >An EDN Blog post about Analog Design tools. [quoted text clipped - 8 lines] > >Robert H. I think Pease has gone senile. Did everyone see his _religion_ rant in the last issue? I went to one of his "seminars", didn't learn a thing, saw a lot of application notes and data books on National's products. As for "...Spice said couldn't work...", what does that mean... Spice couldn't converge on an initial solution? Happens all the time, doesn't mean that the circuit can't work. Show me the circuit schematic and I assure you I can Spice it. ...Jim Thompson | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | America: Land of the Free, Because of the Brave >> From: >> An EDN Blog post about Analog Design tools. [quoted text clipped - 8 lines] >> >> Robert H. He usually says that about the LM331. Cheers, Phil Hobbs >>> From: >>> An EDN Blog post about Analog Design tools. [quoted text clipped - 14 lines] > >Phil Hobbs Anyone have a complete schematic? ...Jim Thompson | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | America: Land of the Free, Because of the Brave >> From: An EDN Blog post about Analog Design tools. >> http://www.edn.com/blog/1480000148/post/240014624.html [quoted text clipped - 16 lines] > > Show me the circuit schematic and I assure you I can Spice it. Inadequate and incomplete models, of course. And unknown or unaccounted-for parasitic elements in the circuit. Happens all the time out there in the real world (i.e., the world that's not IC design). :-) The solution is a painful process to characterize the part, etc., and create a spice model or subcircuit that matches over the range of interest. I also find myself making test PCBs, and taking inductance, capacitance etc. measurements on that. Lots of bench work, serious bench equipment, lots of computer work, plenty of knowledge and experience about what to look for. Given the commonplace absence of this approach, it's rather easy to throw stones at "spice". But given the careful, time-consuming approach, I find spice extremely useful in my push-the-envelope projects. >>> From: An EDN Blog post about Analog Design tools. >>> http://www.edn.com/blog/1480000148/post/240014624.html [quoted text clipped - 30 lines] > But given the careful, time-consuming approach, I find > spice extremely useful in my push-the-envelope projects. Spice is a reasonable general-purpose program for solving systems of nonlinear ordinary differential equations. There are some systems that no program is going to be able to solve, but they're quite rare in applications. Thus just about anything that can be modelled accurately with a set of coupled ODEs can be simulated accurately with Spice. On the other hand, not everything can be modelled with ODEs, not even every circuit. Some better known non-ODE things, e.g. transmission lines, have been put into Spice by hand. (A transmission line's circuit properties aren't given by an ODE because they're nonlocal, i.e. the output undergoes a true time delay.) Other classes of problem that can't be modelled as systems of ODES are transport equations--e.g. the Boltzmann equation for electron transport, or any problem that involves convective motion, such as the air in a heat sink. It isn't great at multiple scale analysis, either, so for instance it would be very poor at modelling the turn-on behaviour of a laser diode, in which time scales from sub-femtosecond (the E & H fields) to hundreds of milliseconds (the thermal transient) all contribute very significantly and nonlinearly. There are codes for this kind of problem, but Spice isn't one of them--it has to follow each cycle laboriously, because a linearized AC analysis won't get the right answer. And anyway, Pease's main complaint is that people use (generally poor) computer analyses as a substitute for thought--and have tried to beat him up with the results over the years. Most of the rest of his posturing is for fun, I think. You can't really make a serious critique of computer simulation by throwing a computer off the roof of the NSC parking garage. Widlar envy, perhaps. Cheers, Phil Hobbs >>>> From: An EDN Blog post about Analog Design tools. >>>> http://www.edn.com/blog/1480000148/post/240014624.html [quoted text clipped - 66 lines] > > Phil Hobbs Thanks. As Win said, "inadequate Models...", could cover a multitude of sins. I wonder how well something like a Flash device's charge storage is modeled in Spice. Robert H. > Spice is a reasonable general-purpose program for solving systems of > nonlinear ordinary differential equations. *Nonlinear* ODE's? Sounds oxymoronic, didn't know there was anything ordinary about nonlinear DE's. > On the other hand, not everything can be modelled with ODEs, not even > every circuit. Some better known non-ODE things, e.g. transmission > lines, have been put into Spice by hand. (A transmission line's circuit > properties aren't given by an ODE because they're nonlocal, i.e. the > output undergoes a true time delay.) Those are actually PDE's... > It isn't great at multiple scale analysis, either, Actually that is what Will Gear's integration mehod was intended to handle, widley varying time scales. > so for instance it > would be very poor at modelling the turn-on behaviour of a laser diode, [quoted text clipped - 3 lines] > problem, but Spice isn't one of them--it has to follow each cycle > laboriously, because a linearized AC analysis won't get the right answer. SPICE probably could be configured to model this, but it's not going to hand it to you on a silver platter. > And anyway, Pease's main complaint is that people use (generally poor) > computer analyses as a substitute for thought-- Nope, Pease's main complaint is not that people use poor computer analyses, it is that they use computer analyses poorly. SPICE is not about solving, it is about producing numbers, numerical integration: http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1301&context=ecetr >> Spice is a reasonable general-purpose program for solving systems of >> nonlinear ordinary differential equations. > > *Nonlinear* ODE's? Sounds oxymoronic, didn't know there was anything > ordinary about nonlinear DE's. An ODE is a DE with one independent variable, which for Spice is usually taken to be time, and they can be linear or nonlinear, with constant or time-varying coefficients. YCLIU. >> On the other hand, not everything can be modelled with ODEs, not even >> every circuit. Some better known non-ODE things, e.g. transmission [quoted text clipped - 3 lines] > > Those are actually PDE's... They're integral equations, because they're nonlocal. PDEs, e.g. Maxwell's equations and the heat equation, are just as local as an ODE--they just have more than one independent variable. I was careful to say that *the circuit properties* of a transmission line aren't given by ODEs, because they aren't. The fields inside the transmission line obey Maxwell's equations, which as you say are PDEs. I'm talking about the two-port circuit behaviour. >> It isn't great at multiple scale analysis, either, > > Actually that is what Will Gear's integration mehod was intended to > handle, widley varying time scales. No, it was designed to handle stiff systems, i.e. those whose eigenvalues are very different in size. Multiple scale is something quite different. YCLIU again. >> so for instance it would be very poor at modelling the turn-on >> behaviour of a laser diode, in which time scales from sub-femtosecond [quoted text clipped - 6 lines] > SPICE probably could be configured to model this, but it's not going to > hand it to you on a silver platter. It could, if you could wait long enough for it to integrate 10**14 cycles, and could handle the resulting extreme roundoff problems. There are better methods, e.g. multiple scale analysis. Bender & Orszag's book on asymptotic analysis is an excellent read on this sort of stuff--and it has lots of great pictures. >> And anyway, Pease's main complaint is that people use (generally poor) >> computer analyses as a substitute for thought-- [quoted text clipped - 5 lines] > integration: > http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1301&context=ecetr Sure, that's what I said--Spice is an ODE integration package, and what Pease doesn't like is that many people use it as a substitute for thought. Anyway, what's the operational difference between wrong answers from bad models and wrong answers from stupid modellers? Cheers, Phil Hobbs >>> so for instance it would be very poor at modelling the turn-on >>> behaviour of a laser diode, in which time scales from sub-femtosecond [quoted text clipped - 12 lines] > on asymptotic analysis is an excellent read on this sort of stuff--and >it has lots of great pictures. The horrible electrical case is time-domain modelling of a crystal oscillator. You need picosecond time steps (or fs, maybe) to resolve the actual frequency, and you may have to run for seconds until it reaches steady-state. Besides, Spice is terrible for measuring frequency. I just model them in the frequency domain, and estimate behavior based on open-loop phase-amplitude plots. >>> And anyway, Pease's main complaint is that people use (generally poor) >>> computer analyses as a substitute for thought-- >> >> Nope, Pease's main complaint is not that people use poor computer >> analyses, it is that they use computer analyses poorly. Nope, Pease's complaint is that people use computers. John >>>> And anyway, Pease's main complaint is that people use (generally poor) >>>> computer analyses as a substitute for thought-- >>> Nope, Pease's main complaint is not that people use poor computer >>> analyses, it is that they use computer analyses poorly. > > Nope, Pease's complaint is that people use computers. Well, maybe...but using them instead of thinking is what he _ought_ to be complaining about. ;) Cheers, Phil Hobbs >>>>> And anyway, Pease's main complaint is that people use (generally poor) >>>>> computer analyses as a substitute for thought-- [quoted text clipped - 9 lines] > >Phil Hobbs Pease lives not far from us. It's funny, his front yard, and sometines the street in front of his house, is always full of rustbucket old Beetles and VW Microbusses. I guess he's just a traditional sort of guy. I've met him a couple of times. He's very nice, one-on-one. John >>>>>> And anyway, Pease's main complaint is that people use (generally poor) >>>>>> computer analyses as a substitute for thought-- [quoted text clipped - 16 lines] > > John I've met him a couple of times at NSC seminars on Long Island. The first time, he was plugging my book (not knowing I was there, of course) and I introduced myself. We got on fine. Of course, in SF people would have VW microbuses on blocks in their front yards...I bet they wouldn't let you have Chevys like us more staid folks. ;) Cheers, Phil >>>>>>> And anyway, Pease's main complaint is that people use (generally poor) >>>>>>> computer analyses as a substitute for thought-- [quoted text clipped - 26 lines] > >Phil Most SF "front yards" might have room for one bicycle up on blocks. RAP lives in a neighborhood that has actual detatched [1] houses and real grass. One of his Electronic Design columns related his skills in repairing rain gutters. John [1] the standard lot, like mine, is 24 feet wide, and houses and roofs are in total contact. One could walk almost my entire block, end to end, on the roofs. [snip] >The horrible electrical case is time-domain modelling of a crystal >oscillator. You need picosecond time steps (or fs, maybe) to resolve >the actual frequency, and you may have to run for seconds until it >reaches steady-state. Besides, Spice is terrible for measuring >frequency. You just need to know how ;-) I regularly simulate start-up in crystal oscillators because that amount of time is part of the specification. >I just model them in the frequency domain, and estimate behavior based >on open-loop phase-amplitude plots. [snip] The best (most stable) crystal oscillators are "sort of" AGC'd. ...Jim Thompson | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | America: Land of the Free, Because of the Brave >[snip] >> [quoted text clipped - 5 lines] > >You just need to know how ;-) So tell me? How can I measure the frequency to, say, 1 PPM in a time-domain sim? > I regularly simulate start-up in >crystal oscillators because that amount of time is part of the >specification. The envelope response is reasonable to simulate in time domain. Phase noise and tempco aren't. >>I just model them in the frequency domain, and estimate behavior based >>on open-loop phase-amplitude plots. >> >[snip] > >The best (most stable) crystal oscillators are "sort of" AGC'd. Yup. Crystal drive matters. But I mostly just buy oscillators now, even OCXOs. OCXOs and TCXOs have really gotten cheap lately. I need a new universal frequency counter. The low-end Agilent looks nice, but it has a crappy XO, and they want another THOUSAND DOLLARS for a mere TCXO. John >>[snip] >>> [quoted text clipped - 8 lines] >So tell me? How can I measure the frequency to, say, 1 PPM in a >time-domain sim? You don't nor do you care ;-) >> I regularly simulate start-up in >>crystal oscillators because that amount of time is part of the [quoted text clipped - 18 lines] > >John ...Jim Thompson | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | America: Land of the Free, Because of the Brave >>>[snip] >>>> [quoted text clipped - 10 lines] > >You don't nor do you care ;-) Oh. Thanks for straightening me out on that. John hmmm... I suppose you could heterodyne it against an ideal generator, and eyeball the difference. > I need a new universal frequency counter. The low-end Agilent looks > nice, but it has a crappy XO, and they want another THOUSAND DOLLARS > for a mere TCXO. Has it got an external input? I've got an ancient (or is that well-aged and "even more stable"?) GenRad OXCO which I can plug into any generator or counter that will take an external reference to make it more accurate. With your rather more serious (than mine) operations, I'd think you could put in one rubidium or cesium reference (and or some new-ish method tied to GPS I'm not overly familiar with) and distribute it throughout your labs/plant/wherever, so long as your counters and/or generators will take an external reference frequency. Assuming decent cable termination and appropriate drivers, I don't see that you'd need more than one "really good" reference.  SignatureCats, coffee, chocolate...vices to live by >> I need a new universal frequency counter. The low-end Agilent looks >> nice, but it has a crappy XO, and they want another THOUSAND DOLLARS [quoted text clipped - 11 lines] >cable termination and appropriate drivers, I don't see that you'd need >more than one "really good" reference. We have an SRS SC-cut ovenized oscillator, that we mounted in a rack box with a power supply. Ditto an ebay rubidium. We even have an old HP cesium standard, which is a big deal to fire up, so we seldom use it. All three typically agree to something like 30 ppb. Cool: trigger a scope from the cesium and look at the rising edge of the rubidium, at 10 ns/cm. Ten minutes later, it's barely moved. But still, a grand for a TCXO is insane. It probably costs them 20 bucks or so. So, no Agilent counter. John > I need a new universal frequency counter. The low-end Agilent looks > nice, but it has a crappy XO, and they want another THOUSAND DOLLARS > for a mere TCXO. Spend you money on a GPS-based super-accurate 10MHz reference to use all around your lab. >> I need a new universal frequency counter. The low-end Agilent looks >> nice, but it has a crappy XO, and they want another THOUSAND DOLLARS >> for a mere TCXO. > > Spend you money on a GPS-based super-accurate > 10MHz reference to use all around your lab. We already have some good 10 MHz sources. But it's a nuisance to have to connect a small, portable counter to a big reference source. Why a grand for a TCXO? John > We already have some good 10 MHz sources. But it's a nuisance to have > to connect a small, portable counter to a big reference source. It should not be. Run some dedicated cables, put on a particular color of heat shrink, leave them there like air hoses or electrical outlets. SignatureCats, coffee, chocolate...vices to live by >> We already have some good 10 MHz sources. But it's a nuisance to have >> to connect a small, portable counter to a big reference source. > >It should not be. Run some dedicated cables, put on a particular color >of heat shrink, leave them there like air hoses or electrical outlets. Distributing 10 MHz all over two floors of a building would be a major project... just for the benefit of one Agilent counter. Ethernet was bad enough. John >>>We already have some good 10 MHz sources. But it's a nuisance to have >>>to connect a small, portable counter to a big reference source. [quoted text clipped - 7 lines] > > John we did that at the capacitor company I consulted at on the side. GPS time base receiver (10 mhz output), into a distribution amplifier with isolated outputs (20 count). each rung went to a work station to be used as the reference for capacitor testers. Signature"I'm never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5 > Distributing 10 MHz all over two floors of a building would be a major > project... just for the benefit of one Agilent counter. Ethernet was > bad enough. I'm sort of surprised that you only have one thing (which you don't even have, if I understand correctly, since you don't want to buy it without the OXCO, and the OXCO is overpriced) that would benefit from easy access to a reference frequency, especially since you have already bothered to get in several reference frequency sources. SignatureCats, coffee, chocolate...vices to live by >> Distributing 10 MHz all over two floors of a building would be a major >> project... just for the benefit of one Agilent counter. Ethernet was bad [quoted text clipped - 5 lines] > to a reference frequency, especially since you have already bothered to > get in several reference frequency sources. The way I read it, I assumed John was talking about pulling all that cable. Thanks, Rich > The way I read it, I assumed John was talking about pulling all that > cable. Yes, I got that. I just find it hard to justify not doing so as "it's only for this one meter I haven't bought, so why bother." Obviously there _are_ other things which he does have that benefit from good references, or he would not have any of those, much less several. Thus, a one-time painful cable-pull-fest would make all those applications, and any future ones (even if he never buys the particular counter in question) easy, rather than a hassle. It's sort of like "Why go to the bother of running all that pipe, when I can get water in a bucket?" Or "Why go to the bother of running all that pipe, when I can drag out a portable air compressor and a hose if I need compressed air?" The way you use things, be they water, compressed air, or 10MHz reference frequencies, changes depending on how much of a pain it is to access them. I suspect that the price of one new counter without OXCO might cover a fleet of older ones from *B*y that will be just fine if they are fed a known-good reference. Some signal generators can also take an external reference for greater precision, if there's one coming to the bench anyway. Enough, I'll stop here. SignatureCats, coffee, chocolate...vices to live by >> The way I read it, I assumed John was talking about pulling all that >> cable. [quoted text clipped - 21 lines] > >Enough, I'll stop here. We have a bunch of HP5370B's, which are 20 ps single-shot time interval counters, that also do frequency to 100 MHz. They all seem to stay within 30-50 ppb of the rubidium, so they don't really benefit from an external reference. But they're 4U rackmount beasts, not something I want in my office mini-lab. I'm in the market for a nice little "universal" counter, preferably new, and haven't found anything really suitable. My Keithley 2100 DVM is a pretty good frequency counter, too, so maybe I'll just wheel over a 5370 when I need something serious. Heck, my TDS2012 is a pretty good counter, too. John >>> I need a new universal frequency counter. The low-end Agilent looks >>> nice, but it has a crappy XO, and they want another THOUSAND DOLLARS [quoted text clipped - 9 lines] > >John So they can sell the 'stripped' version for a grand cheaper to the penny pinchers? Maybe something like that. >From: >An EDN Blog post about Analog Design tools. [quoted text clipped - 8 lines] > >Robert H. Pease has the problem common to columists, out of ideas but deadlines keep coming. He's become an embarassment, but Electronic Design has, too. HoJo seems to be straining, too. John |
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