Fool of The Book - Page 1
Forum section: electronics / general

author: IntegratedValve
author_rank: Regular Contributor
timestamp: September 23, 2013, 07:13:01 pm
content: It's not the first time I got fooled by the titles. I recently I bought a copy of this book:Operation and Modeling of the MOS Transistor by Tsividis and McAndrewAfter reading this description quoted from amazon.com:"Operation and Modeling of the MOS Transistor has become a standard in academia and industry."The industry thing tricked me into something more practical I can use for advanced circuit design using the MOSFETs. All I could find is semiconductor physics and low level behavior of electrons and holes which to me is just useless. I could not even make any use of the equations presented.Anyone tried it and found it helpful in their job?

author: free_electron
author_rank: Super Contributor
timestamp: September 23, 2013, 08:14:43 pm
content: the description on amazon is clear though ...* Energy bands and the energy barrier viewpoint are integrated into the discussion in a smooth, simple mannerhint1 : we're delving in atomic physics here* Expanded discussion of small-dimension effects, including velocity saturation, drain-induced barrier lowering, ballistic operation, polysilicon depletion, quantum effects, gate tunneling current, and gate-induced drain leakagehint2 : this is geometry of the fet structure related stuff. inside workings...* Expanded discussion of small-signal modeling, including gate and substrate current modeling and flicker noisehint3 : substrate ... as a 'user' you don't get to play with that...* New chapter on substrate nonuniformity and structural effects, discussing transversal and lateral (halo) doping nonuniformity, stress and well proximity effects, and statistical variabilityhint4 : there that substrate again.. doping ... proximity effects ... all stuff related to manufacturing of the fet, not the usagehow many more hints do you need ?i agree that it is hard to figure out if a book is going to be useful or not. that is why technical bookshops are valuable. you can browse the book before you buy. but in the above case it is pretty obvious that this is for fet designers. not for designers using fets.

author: Smokey
author_rank: Super Contributor
timestamp: September 23, 2013, 08:58:47 pm
content: Are you looking for practical and accurate SPICE models for current production MOSFETS? So is everyone elseThe really good models like EKV and BSIM that accurately model the characteristics through the whole voltage/current range are not really distributed by the manufactures much (not that I've found at least). Those models actually use the internal structure of the devices and their behavior as parameters for the model, so that's probably why the book goes so far into detail of that.Unless you are willing to spend a lot of money to have a third party lab accurately characterize a device for you, or get super lucky and find someone that already spent that money and is willing to give you their model (good luck with that), you are stuck with less than perfect models that give less than perfect results.What sucks even more is that the current revisions of the algorithms (for EKV at least) are not fully open so even if you wanted to try to make your own model from the data sheet data (which don't always have all the info you need anyway), you can't really make a stand alone solver to check it.There was a really good effort made a while back by a guy from the DIYaudio forum to make an EKV solver based on data sheet info. He gave up because the solver needed so much hand tweaking after it ran and it turned out LTSpice uses a new EKV algorithm that you can't get without an NDA.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 24, 2013, 01:10:52 am
content: During most of the time in which they have existed,MOSFETS were mainly either low level devices used in a linear mode,or they were internal parts of logic ICs.High power switching MOSFETS were nought but a twinkle in some semiconductor designer's eye,as the technology was not available to produce such things.As a Greybeard,I am often bemused by the way "MOSFET" means "big,clunky power switching device" to manymore recent entrants to this field.It's happening with LEDs too--most of the noobs only think of high power lighting applications when they hear the name.

author: amyk
author_rank: Super Contributor
timestamp: September 24, 2013, 12:14:39 pm
content: With the Internet being what it is, you could've easily "borrowed" a digital copy of it to look at first, then decide whether you should buy...

author: IntegratedValve
author_rank: Regular Contributor
timestamp: September 24, 2013, 03:34:29 pm
content: Interestingly MOSFETS main application is digital ICs, beyond that Bipolar rule. But MOSFETS are very popular in academia and professors fell in love with them for some reason...They could focus on writing more useful books on BJT. Anyway...

author: vk6zgo
author_rank: Super Contributor
timestamp: September 24, 2013, 03:50:28 pm
content: Quote from: IntegratedValve on September 24, 2013, 03:34:29 pm*Tell that to all the TV & Radio manufacturers who used dual gate MOSFETs extensively in linear RF applications throughout the 1970s,'80s.& '90s.

author: free_electron
author_rank: Super Contributor
timestamp: September 24, 2013, 04:14:08 pm
content: Quote from: IntegratedValve on September 24, 2013, 03:34:29 pmhave you looked at the catalogue of reputable comapnies like analog devices ? half of their opamps are cmos based..The preamplifiers (the read amplifier) in a harddisk are made in silicon germanium bicmos process. Given that over 2 million drives are made per day... i'd say that's plenty of cmos devices being used in analog...

author: IntegratedValve
author_rank: Regular Contributor
timestamp: September 24, 2013, 04:23:19 pm
content: Quote from: vk6zgo on September 24, 2013, 03:50:28 pm2000s?

author: IntegratedValve
author_rank: Regular Contributor
timestamp: September 24, 2013, 04:24:12 pm
content: Quote from: free_electron on September 24, 2013, 04:14:08 pmHave you looked at GHz bandwidth OpAmps?

author: free_electron
author_rank: Super Contributor
timestamp: September 24, 2013, 06:30:11 pm
content: Quote from: IntegratedValve on September 24, 2013, 04:24:12 pmhow's this for spec:programmable bandwidth corners (30Khz..250Khz low corner 3.2 to 4.6 Ghz high corner in 16 steps )Programmable gain (20 to 60 dB in steps of 1 dB)-3dB point higher than 4.6 Ghz.Phase and gain flat over entire range.many a bluetooth , wlan , gsm transmitters are mosfet based.

author: IntegratedValve
author_rank: Regular Contributor
timestamp: September 24, 2013, 06:43:51 pm
content: I was not aware that MOSFETS are now replacing BJTs even in RF applications...However the maximum bandwidth is still far less than what BJT offer.

author: free_electron
author_rank: Super Contributor
timestamp: September 24, 2013, 08:40:01 pm
content: Quote from: IntegratedValve on September 24, 2013, 06:43:51 pmIntel has a working tri-gate mosfet in 22 nanometer on fully depleted silicon that clocks in at slightly over 1 terahertz. Good luck finding a BJT that can handle that ..And they've had it since 2006 ... no guessing what it does now...

author: Phaedrus
author_rank: Frequent Contributor
timestamp: September 24, 2013, 09:40:33 pm
content: Don't feel too bad about the decline of BJTs. I still see them as high-power, high-frequency switches in SMPS from time to time. Usually in interleaved PFC circuits, I believe. But it's still dominated by FETs.

author: c4757p
author_rank: Super Contributor
timestamp: September 24, 2013, 09:46:36 pm
content: Oh, they'reover1 THz? I thought it was "almost" a terahertz.Damn. That isfast.

author: IntegratedValve
author_rank: Regular Contributor
timestamp: September 24, 2013, 10:04:39 pm
content: Ok then I'm wrong and got my information wrong. And my answer on one post was wrong too, BJT is getting obsolete. Perhaps the preference is debatable and rather personal than based on scientific facts. MOSFET kicked the BJT's ass in all areas.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: September 24, 2013, 10:29:15 pm
content: MOSFET proved equivalent or superior to BJT in enough areas to become the default, and BJT is being reduced to niche areas where its strengths still outshine MOSFETs. There's nothing personal about that. Clinging to and defending a specific technology just because it is no longer the de facto industry standard does strike me as a personal problem though.

author: free_electron
author_rank: Super Contributor
timestamp: September 24, 2013, 11:21:43 pm
content: BJT is not disappearing. both BJT and mos have their uses. BiCMOS process combine the best of both worlds.For low power operations MOSFET's will win simply because there are no bias currents. only bias voltages. no current means no power consumption.I would never use a BJT to turn on an LED for example. You need a base resistor and a transistor. And the transistor consumes current. slap in a 2n7002 and done. you save a resistor in the BOM and there is no static power consumption from the transistor. Instant win-winon the other hand if i need a circuit that requires a BJT i will not attempt to replace it.Both have their place. And both are useful.Technology moves fast. very fast. and the speed at which it evolves is still increasing.

author: Smokey
author_rank: Super Contributor
timestamp: September 24, 2013, 11:26:20 pm
content: Isn't there some sort of fundamental limit in the Thz range based on electron velocity?

author: tom66
author_rank: Super Contributor
timestamp: September 25, 2013, 12:06:18 am
content: I thought BJTs were faster than MOSFETs, but the main reason you don't see a Core i3 made with them is it'd need to dissipate several tens of kilowatts instead of 65W.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 25, 2013, 03:54:36 am
content: Quote from: IntegratedValve on September 24, 2013, 04:23:19 pmIn the early 2000s,due to alleged poor dynamic range,(although many people have never experienced any problems from this) designers moved away from dual gate CMOS discretes in the early stages of high performance HF receivers,but they still appear in other equipment where immunity to nearby powerful signals is not so important.In many cases they are now part of a linear IC with many functions.Bipolarshavemade a comeback in RF preamp stages at UHF & above----germanium ones,at that!!The reasons for this are,generally lower noise & better dynamic range.That said,plenty of GASFETs & even 1980s vintage dual gate MOSFETs continue in service.The great thing about dual gate MOSFETs is that they are so easy to use as preamps.mixers,AGC controlled IF stages,etc.The extra gate allows great flexibility --one device,-v- two or more with bipolars,JFETs,etc.,

author: vk6zgo
author_rank: Super Contributor
timestamp: September 25, 2013, 04:04:02 am
content: Actually,in the previous posting,I should have used BJT instead of the more sloppy "bipolar",as years ago one or two manufacturers made what they at that time called a "bipolar" transistor.Its claim to fame was that emitter & collector were interchangeable---I'm sure there was some advantage to this,but it is beyond me!!I thought I'd just add this so someone with an even longer,greyer beard didn't pick me up on it!

author: madsci
author_rank: Regular Contributor
timestamp: September 25, 2013, 05:40:30 am
content: It is indeed the standard in academia. Those equations were the bane of my existence last semester....especially because my prof LOVES proofs.We had toderivethem on the exams. The other professor gave you the equation and expected you to use it. We had to conjure it up using diff-eq.Did I mention my academic adviser slotted me in that course with Differential Equations as a concurrent? Yeah, it was rough.

author: IntegratedValve
author_rank: Regular Contributor
timestamp: September 25, 2013, 04:32:49 pm
content: QuoteYeah I know prof's love proofsbut do they really use such equations in making FETs? or at least did they use all this math before they made the first FET? Or is it academia fart?

author: IntegratedValve
author_rank: Regular Contributor
timestamp: September 26, 2013, 04:42:19 am
content: Quote from: wilfred on September 25, 2013, 10:44:00 pmI believe things when I see them in action, so proofs can be sit on the bookshelf. Why should I learn about electron life-cycle inside these devices while I cannot put them in a useful design??? How can I design such devices if I don't know how they work from outside???I've been reading about semiconductor devices and how they work since very long but could never make sense of any not intuitively...and I bet you the authors don't know either, all copying and repeating the same bla bla bla...at least no creativity in explaining the amplification action at the electron/hole level.I believe that such devices work but I don't buy it when it comes to interpret things at the very low level...remember atomic structure keeps changing all time.

author: madsci
author_rank: Regular Contributor
timestamp: September 26, 2013, 06:39:29 am
content: I have my doubts that deriving the equations themselves is useful for an undergrad student. It's not like I can make a BSIM model that's worth a darn from just a datasheet.

author: KJDS
author_rank: Super Contributor
timestamp: September 26, 2013, 10:02:42 am
content: Quote from: vk6zgo on September 25, 2013, 03:54:36 amThe last LNA I put into production used InGaP pHEMT, 0.3dB noise figure at 850MHz. I'd be interested to know of anything other than a pHEMT that would achieve that noise figure.