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| MOSFETs versus BJT in discrete designs |
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| David Hess:
--- Quote from: mawyatt on November 22, 2023, 05:14:13 pm ---Yeah that's always been an issue, even the CMOS ADCs have this "feature" and why one must pay close attention to the driving source impedance/dynamics of the source driving said ADC. Some Op-Amps were/are specifically designed to drive these Hi Speed ADC inputs without significant induced "ringing" for the dynamic charge injection. Heck even DMMs can do this, we had one long ago (can't remember name tho) that corrupted anything active it measured, a swift hammer correct this potential future problem ;) --- End quote --- I keep my oldest Tektronix bench DMMs in repair because their linear differential JFET input stage produces no charge injection. They can make some difficult measurements that modern DMMs cannot always be relied on to make accurately. --- Quote from: Someone on November 22, 2023, 10:27:56 pm ---There are chopper parts coming into the market where the manufacturer is confident in use at "high" impedances. OPAx189 is pretty well proven at this point. --- End quote --- I have heard that before from marketing. In the past it meant they found a new way to obfuscate input current noise specifications in their datasheets. I will have to get some OPAx189s to test, and Analog devices has a similar part, however from the OPAx189 datasheet: Zero-drift amplifiers such as the OPAx189 use switching on the inputs to correct for the intrinsic offset and drift of the amplifier. Charge injection from the integrated switches on the inputs can introduce short transients in the input bias current of the amplifier. The extremely short duration of these pulses prevents the pulses from amplifying, however the pulses may be coupled to the output of the amplifier through the feedback network. The most effective method to prevent transients in the input bias current from producing additional noise at the amplifier output is to use a low-pass filter such as an RC network. |
| coppercone2:
--- Quote from: mawyatt on November 23, 2023, 12:54:56 am --- --- Quote from: coppercone2 on November 22, 2023, 04:42:11 pm ---what we need is cheaper fabs so we can get what we want instead of relying on piggyback crap things may not be as grim as you imagine if fab tech gets economized or new construction methods for transistors occur. Some kind of new manufacturing machine. The 3d printer was amazing, maybe there is something that can be made for larger transistors. Years ago I heard the same thing about plastic parts that you will never be able to get high quality complicated plastic parts without a tool and die/mold guy, its only kind of true, even for high quality metal parts. FAB are vastly overpriced because of the secrecy too. I know that. even adding useless steps to throw off the competition or obsfurate manufacturing technique. and its pretty easy to find someone that says they were ignored about process improvements. All the fab stuff is so tight budget its all based on probability of projections coming through to put ANY money into improving ANYTHING. This is mostly based on hearsay amongst businessmen.... you might consider alot of tech being left behind at a expensive legacy level simply because the bosses think demand might decrease making it unprofitable based on the company history not the cost of the capital (true for any technology outside of the say middle 25% of the bell curve in terms of actual demand and projections). That is, the line runs with the upmost priority being lowest possible severance costs (meaning absolutely bare minimum input towards upkeep and zero input for improvement, for instance something as simple as replacing some manual pressure gauges and valves with a PLC that automates part of some process at costs under 10k dollars when its not even the cost of a months return). this kind of stuff exists! It sometimes even happen because there is no growth expected, even if the demand is not expected to change, if the business strategy chosen happens to be "only put money into things that are likely to grow! we are not even interested in reducing day to day and manufacturing cost because we might grow elsewhere, its what the board wants this quarter!!!!!" this results in something being unbelievably bad but IT EXISTS!!!!!! and if someone wants to do a external industry-info cost study of such a thing, you will get a fucking stone wall bullshitter that makes you think its all running at peak fucking efficiency and its been studied to death, your talkin north korea levels of honesty here and then there is the geopolitical side of things. that can make it extra stupid. like mega. when you involve washington, and the pentagon, into costs, the ramifications are only the limits of peoples imaginations. --- End quote --- Obviously you don't have a semiconductor background, nor bother to study up on things related. Today a new SOTA CMOS fab costs north of $25B, takes over 5 years to come on line and produce the first penny of revenue, and requires continual investments per year well over $1B just to keep up!! TSMC is leading the CMOS charge followed by Samsung, and Intel trying to play catch up!! The USG is trying help the US catch up to what they let out of the bag long ago, thanks to both DC parties involved, and now eventually trying to help US semiconductor technology play catch up. TSMC with some USG $ assistance, is building 2 SOTA CMOS fabs in US (Az), but coming on-line being delayed because of lack of high level US semiconductor talent, embarrassing indeed!!! Apple's new M3 chip sets are in TSMC 3nm CMOS process and the most advanced chip has 25 Billion MOS transistors!! If a transistor costs just 1 penny, this chip would cost $250,000,000.00 and yet you can buy a complete Apple computer today for considerable less!! Good example of the massive semiconductor investments paying off in the long run, hopefully someday Apple and Nividia chips will be fabricated on shore!! We still have a few shinning spots in US advanced technology, semiconductors used to be at the top of that list, but sadly has faded over the years, hopefully the future will bring some of this technology back home. BTW I do recall something about plastic transistors from way back, and some guy making chips/transistors in his garage, but can't remember details. Funny, that made me think of as a kid about 10~11 getting a couple diodes and connecting them to make a transistor :o Best --- End quote --- the ones you mention are the hot '25 percent' of the semiconductor manufacturing world. I mean idk the real percentage, but those are the hot looked at ones right now. what I am saying is that some esoteric old op amp process might not have had so much care and optimization and modernization / honest cost analysis done on it, making it possible to improve and not quite so expensive as originally quoted, if bright people are working on it that don't have really strong corporate 'guidelines' holding them back. like my gut feeling from what I have seen and heard is that probobly they don't incorporate as much new technology or optimize the process as much as we think or even spent time researching how to improve or bypass hard parts of the process because of it simply being uninteresting to the R&D elements of a company if they are told to only work on GROWTH areas not STEADY INCOME areas. They often seem to want to focus on things that have MASSIVE potential not incremental improvements. Like they need to do something to look like the promise they made about the GROWTH of the company, which attracts investors, is being honored. What gets people interested is 'we are a 150 million dollar company looking at being a 5 billion dollar company in 3 years' not '300 million'. They just know the market well enough to know that despite the fact there might be good money to be made, its not the kind of money that keeps people interested in supporting them! that is like talking about 5th avenue and forgetting about the bronx like it goes hand in hand with moores law. investors love moores law. it means their money has geometric growth potential. the company is looking at ways to at least look like its trying to grow geometrically or whatever the hell you call moores law curve. if their not doing that then its often considered a bad company. like think big shoot for the stars type stuff. because someone is gonna make that promise elsewhere and their gonna take their money else where. so its like 'nah we don't waste our time on that old shit just keep it running titrated to the nearest cent'. But behind the scenes there might be enough data and insight gained to make pretty massive improvements (in terms of available industry research, and company know how, and realizations about exactly what you need to pass QC), just its not agreeing with moores law, so its kinda put to the side, even if its a mainstay. And the contracts I imagine don't make it easy to change nothing, like lawyers get involved, you could pin a delay on someone 'messing' with the production... exposure... |
| PartialDischarge:
I’ll leave this article here, it’s old but with some interesting thoughts, the author is an expert in power electronics and very smart guy |
| mawyatt:
Interesting read, thanks, but as you mentioned quite old (1993). His conclusion hints at an improved Si bipolar transistor structure for high speed and power applications, which we don't recall seeing. At that time Power MOS was beginning to made some inroads into SMPS use with the Siliconix VMOS and IR HexFET technologies which he fails to mention. Today believe most new SMPS designs are utilizing some form of MOSFET, especially new SMPS chips. For higher Power Density which implies smaller magnetics and thus higher switching frequencies the GaN FET is beginning to win new designs for the main power switching device. Anyway, the power sector of semiconductors is rather special case compared to the massive digital CMOS world, but also seems to be yielding to CMOS for the lower to moderate power levels, with some special CMOS technologies for higher voltage use with direct mains SMPS now available. If you look at the popular mains USB power modules, the new designs seem to all be CMOS based. Edit: Remember being on a panel session with Dr. Tom Lee from Stanford in the early renditions of what later became the RFIC Symposium at the IEEE MTT back in 90s. Believed that SiGe bipolar technology would continue into the future and grow due to the many advantages of SiGe bipolar over CMOS, Tom thought otherwise that CMOS would eventually dominate in spite of the SiGe advantages, well guess who was right ??? Best, |
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