Q1:When I doing VLSI design, I remember that somebody told me never to use bipolar ( our process is standard cmos process ), because it is expensive ( ? really? )
Q2:When I doing discrete design, I saw a lot of bipolar here, and someone told me that FET is expensive. ( about two times than npn/pnp transistors )
Q3:and if I use a NOT gate chip that is also expensive than two FET ( nmos + pmos inverter )
Q4: I don't have too much idea about the price for FET / transistor / not gate ..etc, where can I get them ? ( what can I only do is to froogle it ... )
Q5: What is the condition you decide to use a MOS or transistor ?
This is really the chip designer's territory but maybe bipolars use more silicon 'real estate'. Bipolar circuitry tends to use more power too.
Discrete fets are indeed more expensive than bipolar devices.
An IC inverter is more expensive than a discrete one made from fets ? Unlikely. There are some cute 'baby' chips now that contain single inverters/gates instead of having to buy 4 or 6 in a package.
Manufacturer's website perhaps ? Many give 1k qty pricing.
e.g.
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A device I use. Pricing is as low as 2.3 cents @ 1k qty ( see the table )
Depends on the application. Discrete designers will typically use bipolar unless there's a specific reason to use a fet.
BJTs in VLSI are used mainly for driving Current-demanding circuitry and they are bulkier than CMOS devices. So, the answer depents on what your circuitry needs to do
You would do well to have access to catalogs from the following distributors (you may have observed us providing specific links and prices here on s.e.d.), and become familiar with their websites,
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There are many others I also use, but these have the best catalogs to learn from. You would also find AoE's component tables useful. Once you start finding your way around popular discrete parts you'll no doubt learn about local distributors who are easy to work with, even if they don't have huge staffs creating massive fancy catalogs.
A1)& A2) In industrial R&D "somebody said" is not used A3) On mass production we listen carefully to supply department, that's IS their expertise. A5) Past experience in solving similar problems, MTBF and warranty costs, existing parts in stores and so on and on...
In the end the finished part is usually sold to customer with working specs ~50% of the manufacturers advertising sheets.
True. As Win said keep a distributor web site open at all times when designing discrete circuitry. I usually have Digikey and Arrow open. Then gradually learn the cost of the most often used parts by heart so you don't even have to look at the other PC screen. When you get good at this you can predict the cost of your whole design to within 20% before running the BOM.
Try an example: On Digikey enter MMBT3904 and you'll find it around 1.5 cents. Now enter BSS123 and you'll see that it costs almost 5 cents. That is why I agonize over the use of a FET quite some time on high volume products. Do I really, really need a FET here? If there is any way to do it with bipolar transistors I'll do it. Even with 0.8 cents or so added in for the burdened cost of a base resistor the BJT typically wins. If you go for off-brand BJT you can sometimes get them into the BOM at well under one cent (Asian sources, mostly).
Go to Digikey, it's all there. You can buy a non-buffered 74HCU04 for under 10 cents. It contains six nmos/pmos pairs and you can do marvelous things with it. There is no way to buy 12 FET for that kind of money.
Unless I need the functionality of a FET this boils down to one reason: $$$
It is more than 30 years old now, but I HIGHLY RECOMMEND that you read and thoroughly understand the CD4007 data sheet. If you want 3 PMOS transistors and 3 NMOS transistors in one package and with some individual terminals accessible and others bussed for complementary pair use, then the CD4007 fills many of the needs most of the time.
The CD4007 is often lumped in with the CD4001 digital logic series but it isn't necessarily digital. Most clever uses come from using it in analog ways.
Also closely examine the ULN2003 data sheet (7 common-emitter NPN drivers) etc. as you seem to be struggling with bipolar drivers.
Neither represent high integration anymore but they are workhorses still.
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