WHICH IS FAST? BJT or MOS

[funnynypd]

whether bjt is faster or mosfet

BJT has larger power consumption rate and two kind of carriers. Also it use current to control current.

CMOS only use one type of carrier and use voltage to control current.

THe speed depends on physical layout, current, manufacturing process, etc. Check the detail datasheet from manufacturer will give what you want.

 

[Yasser A.Nour]

mos bjt design

The BJT is faster than MOSFETs*** for that reason the TTL family is faster that CMOS family
but the BJT consumes power statically and dinamically so it has high power consumption

 

[Element_115]

bjt or mosfet faster

Can you clear up some thing.

Are you talking about Process/technology: MOS, CMOS, BiCMOS, SiGe....

Or BJT's vs. FET's ?

Are you assuming highest frequency to be amplified is your merit of Speed,
(Frequency response of the device "S21")
or
How fast the device can transition from a Low to High state is your merit of speed?
(Max data throughput)

 

[tibm]

mosfet mos bjt

MOS is better than BJT due to the technology involved
Further as far as switching speed is concerned MESFET(Metal Semiconductor FET) and MOSFET(Metal Oxide Semiconductor FET) is used depending on application ........ MESFET usually finds its application in Microwave circuits.

 

[xylynn]

plz all of u give a good decription.... b'cause the readers complicate what u say

 

[yeechyan]

The power MOSFET has the advantages of the majority carrier devices, so it can achieve very high operating frequency. Compared to the MOSFET, the operating frequency of the IGBT & BJT is relatively low, mainly because of a so-called 'current-tail' problem during turn-off. This problem is caused by the slow decay of the conduction current during turn-off resulting from slow recombination of large number of minority carriers.

 

[funnynypd]

some of today's MOSFET design can be controled by TTL voltages.

 

[rajanarender_suram]

I think BJT is faster and if I remember it right one thing That MOS cannot do better than BJT is that BJT has Higher frequency Response. But others prefer MOS because of its lower size and lower power consumption.

Everyone whose saying Bjt is faster better read this........MOS is 100% faster...........Bacause as its name suggests.....Metal Oxide Semiconductor ,It has high input impedance which makes it much faster than BJTs........


Ishan
Electronics & Telecom. Engineer

As of i know the BJT is faster than mos hence they are used at higher frequencies,

Ishant what is the relation for higher input impedance and speed ??????

 

[faraz7777]

As a general answer we should select BJT as the faster one... BUT when we say about the switching and digital ckt, CMOS is the winner, since its newer technology helps it to use narrower channels to get the winning speeds.
In analog ckt, when we don't use a BJT is saturation mode,and it is in its active mode, it shows faster than Mos tech; since there is no need to involve with huge carriers in this case.

 

[JuegoMaestro]

I hope this clears up the misunderstanding.

mos is much slower than bi-polar (BJT) and I will tell you why. If any of you are an EE or CE and took VLSI you should have been tought the physical structures of both of these transistors. Lets start with mos. You have a p-substrate with 2 n-wells being separted by a thin silicon oxide layer. so the current is flowing sides ways from drain to the source. the gate sits right above the oxide. upon a voltage on the gate a channel is developed along the thin oxide to complete a connection. So an easy way to think of this is by holding your hand up flat and horizontal in front of you (this being the channel). The current will actually flow from from the sides of your hand... mean having the smallest amount of contact surface area. now this is where BJT differs from mos. Bjts current actually flows vertically from the top of your hand down. Thus, a much larger surface area for current to flow. this allows the transistor to turn on and off quickly therefor you can run at much higher clock rate. (study VLSI)

Now you may ask why did they give up on the bi-polar idea and picked up the cmos. Well for many reasons CMOS transistors can be designed much smaller than BJTs. there can be at least 4 cmos transistors that could fit in the area of a BJT and they just continue to find ways to make cmos transistors smaller. Second reason is the power dissipation issues. Because mos has a much higher impedeance they dissipate less heat. Because of the larger surface area of contact of BJT and more often they are on they produce much more heat.

So many of you have been noticing Cmos is not getting any faster. Why? Well it certainly not because they can't make the transistors smaller. Transistors are getting smaller but they are finding that the copper traces are not scaling well. This why research is being put into optical and carbon nanotubes. Carbon nanotubs have amazing electrical properties but they are having a problem fabricating them. Multi cores are not doing well either. The only thing that has been found to parallelize well is graphics and servers. check out amdahl's law to find more information on this.

 

[si14]

For the design of Low Noise Amplifier, which one is better, BJT or FET?
Another question, how can I test a FET, and see whether it's unharmed or not?

 

[xulfee]

i think mosis faster

 

[neils_arm_strong]

@nan_ishan
Does High impedance mean faster performance ??

 

[siongboon]

I don't think so that
high impedance means high speed.

I think high impedance provide better isolation.

Best Regards,
Siong Boon

 

[Dharmander Malik]

The extrinsic or circuit speed of Bjt is faster than Mosfet because bjt has larger capacitance to charge or discharge the load capacitance, but their extrinsic speed are equal.
Source :- Fundamentals of solid-state electronics
By Chih-Tang Sah page 906
direct link of page :- Fundamentals of solid-state electronics - Chih-Tang Sah - Google Books

The switching speed of mosfet is larger than bjt because of absence of minority carrier charge sorage phenomena.

 

[the_falcon]

Definitely BJT is faster than MOSFET because of the higher gm factor
MOSFET is capable of having higher density than BJT and so its famous in one way out of many other specific advantages associated with MOSFET

---------- Post added at 14:32 ---------- Previous post was at 14:27 ----------

CNT MOSFETS have been started to get fabricated nowadays
the output resistance is horribly small and so the electrical model is in a tuff situation to get matched with the ideal one.
but still its a great step which has to be appreciated for sure

falcon

I hope this clears up the misunderstanding.

mos is much slower than bi-polar (BJT) and I will tell you why. If any of you are an EE or CE and took VLSI you should have been tought the physical structures of both of these transistors. Lets start with mos. You have a p-substrate with 2 n-wells being separted by a thin silicon oxide layer. so the current is flowing sides ways from drain to the source. the gate sits right above the oxide. upon a voltage on the gate a channel is developed along the thin oxide to complete a connection. So an easy way to think of this is by holding your hand up flat and horizontal in front of you (this being the channel). The current will actually flow from from the sides of your hand... mean having the smallest amount of contact surface area. now this is where BJT differs from mos. Bjts current actually flows vertically from the top of your hand down. Thus, a much larger surface area for current to flow. this allows the transistor to turn on and off quickly therefor you can run at much higher clock rate. (study VLSI)

Now you may ask why did they give up on the bi-polar idea and picked up the cmos. Well for many reasons CMOS transistors can be designed much smaller than BJTs. there can be at least 4 cmos transistors that could fit in the area of a BJT and they just continue to find ways to make cmos transistors smaller. Second reason is the power dissipation issues. Because mos has a much higher impedeance they dissipate less heat. Because of the larger surface area of contact of BJT and more often they are on they produce much more heat.

So many of you have been noticing Cmos is not getting any faster. Why? Well it certainly not because they can't make the transistors smaller. Transistors are getting smaller but they are finding that the copper traces are not scaling well. This why research is being put into optical and carbon nanotubes. Carbon nanotubs have amazing electrical properties but they are having a problem fabricating them. Multi cores are not doing well either. The only thing that has been found to parallelize well is graphics and servers. check out amdahl's law to find more information on this.

 

[DartPlayer170]

Re: is bjt faster than mosfet

BJT is faster in the linear region but becomes slower as a switch when it is driven into strong saturation.
Even though Ft is generally higher, the turn off delay impairs the switching time for BJT depending on the design.
Ultimately the answer depends on the design of the circuit not the type of transistor.