CMOS and transistors differences.

[Boki]

Hi All,

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 ?

Best regards,
Boki.

 

[Pooh Bear]

Hi All,

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? )

This is really the chip designer's territory but maybe bipolars use more
silicon 'real estate'. Bipolar circuitry tends to use more power too.

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 )

Discrete fets are indeed more expensive than bipolar devices.

Q3:and if I use a NOT gate chip that is also expensive than two FET (
nmos + pmos inverter )

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.

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 ... )

Manufacturer's website perhaps ? Many give 1k qty pricing.

e.g. http://www.fairchildsemi.com/pf/BC/BC550.html A device I use.
Pricing is as low as 2.3 cents @ 1k qty ( see the table )

Q5: What is the condition you decide to use a MOS or transistor ?

Depends on the application. Discrete designers will typically use bipolar
unless there's a specific reason to use a fet.

Graham

 

[Hlrsr]

Hi All,

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 ?

Best regards,
Boki.

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

GM

PS:Sorry for my English

 

[Boki]

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. http://www.fairchildsemi.com/pf/BC/BC550.html 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.

Graham

Great thanks!

Best regards,
Boki.

 

[Winfield Hill]

Boki wrote...

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 ... )

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,
http://www.digikey.com/ http://www.mouser.com/ http://www.jameco.com
http://www.newark.com/ http://uk.farnell.com http://www.alliedelec.com/

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.

 

[Stanislaw Flatto]

Hi All,

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 ?

Best regards,
Boki.

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.

HTH

Stanislaw
Slack user from Ulladulla.

 

[Joerg]

Hello Boki,

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? )

Sometimes you have to use them.

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 )

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).

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 ... )

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.

Q5: What is the condition you decide to use a MOS or transistor ?

Unless I need the functionality of a FET this boils down to one reason: $$$

Regards, Joerg

 

[Tim Shoppa]

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 ?

Boki:

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.

Tim.