Why we use MOS family if BJT has better GAIN or BW?

• Jun 10, 2004

• #21

duncan94022

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Re: Why we use MOS family?

duguzhang is the only one that really answered the question: MOS transistors are better because they don't exhibit minority charge storage effects. Therefore they switch faster (because you don't have to wait for low mobility minority carriers) and therefore they dissipate less power. Because they use the "field effect" and don't require vertical current flow like a BJT, they can be made much smaller. Everything else falls out of these two facts.

 

• Jun 11, 2004

• #22

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alphi

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Re: Why we use MOS family?

to open some BJT and mos datasheet,I think you can find their merit.

 

• Jun 14, 2004

• #23

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zanov

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Re: Why we use MOS family?

Actually price is an important role but dont forget the main reason which is permanent: power. Does power cost money? The chip all the time needs power.

Guys what do you think for LinMOS power saving technology?

 

• Jun 15, 2004

• #24

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micel99

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Why we use MOS family?

People still use BJT. In opamp design, very high slew-rate and bandwidth can be achieved by it. But life is not always so critical. I think most advantages of MOS are on digital point of view.

 

• Jun 16, 2004

• #25

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Charlie.za

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Why we use MOS family?

CMOS have symmetrical noise margin, high input and low out impedance, high gain in transition region, high packing density and low power dissipation with respect to BJT techology. But the restricting factor is speed. Therefore you can integrate MOS with BJT for improvement output currents.

 

• Jun 21, 2004

• #26

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s.b.f

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Re: Why we use MOS family?

it has some features that makes it more suited for use:
1. ease of fab
2. high integrity

3. its high input imp.
4. its low power consumption
5. its rail to rail sewing

 

• Jun 21, 2004

• #27

lord_of_destruction

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Re: Why we use MOS family?

Bjt is better than mos in both gain and BW
it's also faster
but the mos advances bjt in
it's very high input impedance due to the use of oxide
it's easy fabrication and easy scaling technology that makes its speed very high and near to bjt
lower cost
low power consumption since scaling gives it ability 2 use lower supplies
and it's symmetical device unlike bjt
in digital we can see that mos is a faster switch since leakage is very low compared to bjt

 

• Jun 21, 2004

• #28

lord_of_destruction

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Re: Why we use MOS family?

duguzhang said:

Physically speaking, BJT is minor carrier conducting device and CMOS is major carrier conducting device.

BJT has its own advantages such as higher gain and higher current driving capability.

Click to expand...

sorry but i guess bjt is a majority carrier device as NPN carriers are electrons while mos is minor carrier since we make a channel opposite to kind of used SC like n-channel

 

• Jun 22, 2004

• #29

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Hughes

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Re: Why we use MOS family?

lord_of_destruction said:

sorry but i guess bjt is a majority carrier device as NPN carriers are electrons while mos is minor carrier since we make a channel opposite to kind of used SC like n-channel

Click to expand...

Bjt IS a minority carrier conducting device and CMOS IS majority carrier conducting device. Electrons in NPN bipolar transistor's emmiter area are majorities, but electrons ejected into base area are minorities. In NMOS, the channel is n-type when the device turns on, so electrons from source are majorities in channel.

 

• Dec 10, 2004

• #30

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ashish sharma

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Re: Why we use MOS family?

c there is al ot of diff between the two and if you really wanna discriminate go for a specific problem oriented discrimination so as to reveal the facts to you. post a specific application where you wanna use them and may be i will help you in this matter.

greets!

 

• Dec 10, 2004

• #31

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amarnath

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Why we use MOS family?

cmos is basically used because of its high integration density,zero static power dissipation,high noise margin and many more.

regards
amarnath

 

• Dec 10, 2004

• #32

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konqueror

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Why we use MOS family?

cmos has a very high density so more mos transistors can be integrated on one chip.besides these if cmos ckts. are used they consume less static power.bjts are very fast but consume a lot of power.

 

• Dec 12, 2004

• #33

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boot_strap

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Re: Why we use MOS family?

hi
Low power

 

• Dec 13, 2004

• #34

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DrDolittle

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Re: Why we use MOS family?

For switching operations CMOS is better than BJT,therby this goes digital.As dar as the area of the device CMOS occupies lesser area therbby giving a better compaction inside a chip.As per ashish sharma,be specific in your applicaion.

Regards
drdolittle

 

• Mar 4, 2007

• #35

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maharshi_qis

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Re: Why we use MOS family?

Becoz it is giving us economically more advantages than BJT interms of fabrication,control,logic levels etc..