Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

BJT is faster than MOS-Every reply will b clicked helped

Status
Not open for further replies.
N

nan_ishan

Member level 5
Member level 5
Joined
Oct 29, 2007
Messages
88
Helped
13
Reputation
26
Reaction score
3
Trophy points
1,288
Location
Nasik-India-Asia
Activity points
1,865
HI guys this one is for those who think that MOS is faster than BJT.
Actually BJT is faster than a cmos.
The reason behind this is that MOS has a high input capacitance which lowers the speed .
Although,Cmos is mostly used ,it is due its other advantages....which you all know and there's no need to mention..........
Here is the proof:

https://www.allaboutcircuits.com/vol_4/chpt_3/7.html


Bipolar transistors are used preferably when large load and speed are needed:
given in:

**broken link removed**

I'll click helped to everyone who replies,just say whether u agree or not.I have clicked helped to everyone who has posted a reply(the intention is just to spread knowledge.....)
 

Hello, there are other factors that are also important in determining bandwidth of a transistor. first of all it is true that input capacitance of MOSFET is higher but question is how much> with typical input capacitance of 120pF and output impedance of driver 100 Ohm it still has about 13MHz bandwidth. Some BJT transistors have even poorer bandwidth. One important factor in BJT bandwidth is speed of base-collector diode. while usually base-emitter is much faster that base collector diode, the base collector diode can restrict bandwidth of BJT. you should look at datasheet of each transistor some BJTs are faster than MOSFET some do not.
regards,
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
bjt is faster than mos... only by scaling mos has been made to approach higher speeds...
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
mosfet has a faster turnoff time , and the gate drive circuit can be designed to supply some few extra current to rapidly turn on the mos, also note to this expression from abraham pressman in the "switching power supply design" book ,chapter 9-introduction :
"the faster switching speed of MOSFET's has permitted increasing power supply switching frequencies from about 50 to 200 or 400 KHz."
.
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
is_razi said:
mosfet has a faster turnoff time , and the gate drive circuit can be designed to supply some few extra current to rapidly turn on the mos, also note to this expression from abraham pressman in the "switching power supply design" book ,chapter 9-introduction :
"the faster switching speed of MOSFET's has permitted increasing power supply switching frequencies from about 50 to 200 or 400 KHz."
.
Click to expand...

It does'nt mention that Mosfet is faster than BJT anywhere
 

As a matter of fact, the first advantage of CMOS ckt is its lower energy consumption, and the ability of usage with several levels of voltages... eg. we need 5 volt for BJT 74xxx ICs, but not necessarily for 74cxxx ones.
However, in some cases we may see a very fast modern CMOS IC which has reached good comparable speeds with JBTs.
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
Nice find.
Thanks
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
not only MOS takes less space, less power, it can work on lower voltages...
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
MOS is faster then BJTs as i think it for the switching delays.
for BJTs certain amount of current is to b maintained if we have to driver some circuit and that will depend upon the B(beta of BJT)

but for CMOS we can get sharp rise and falls of voltage for its switching as compared to BJT which will take some delay to aquire a value of current
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
ehsanelahimirza said:
MOS is faster then BJTs as i think it for the switching delays.
for BJTs certain amount of current is to b maintained if we have to driver some circuit and that will depend upon the B(beta of BJT)

but for CMOS we can get sharp rise and falls of voltage for its switching as compared to BJT which will take some delay to aquire a value of current
Click to expand...
did u check out d links posted by me
 

did u check out d links posted by me
can u post them again to the below given addr please
"parimisys@gmail.com"
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
thanks a lot
hey did u watch the topic "design of bot" posted by me
try to reply that please
 

nan_ishan said:
ehsanelahimirza said:
MOS is faster then BJTs as i think it for the switching delays.
for BJTs certain amount of current is to b maintained if we have to driver some circuit and that will depend upon the B(beta of BJT)

but for CMOS we can get sharp rise and falls of voltage for its switching as compared to BJT which will take some delay to aquire a value of current
Click to expand...
did u check out d links posted by me
Click to expand...

yes i did but there was no thing new in 1st one
and 2nd one yes good but i got only the overview as it is very difficult to read the whole page on screen
 

ehsanelahimirza said:
yes i did but there was no thing new in 1st one
and 2nd one yes good but i got only the overview as it is very difficult to read the whole page on screen
Click to expand...

Check the review topic at the end of page in first link...

This line is form second link:Bipolar transistors are used preferably when large load and speed are needed:
 

hello nan_ishan, your comparison is not correct. As I said there are many factors that determine bandwith of BJT or MOS. There are fast MOS, slow MOS, fast BJT, slow BJT. each of them are useful for a purpose. If you mean what will be speed limit of these technologies. Well at least I have not seen MOSes that can go beyond 1GHz but ther are BJTs that can operate happily in microwave area.
regards
 

    N

    nan_ishan

    Points: 2
    Helpful Answer Positive Rating
fala said:
There are fast MOS, slow MOS, fast BJT, slow BJT. each of them are useful for a purpose.
Click to expand...

thats the basic theme for this topic according to me.

actually MOS or BJTs, selection depends upon type of application and what power involved to drive or to be driven.
motor driving circuit, high VA power supplies/inverters, switching power supplies and memory elements, some times we look for power not the delay but some time exact timings are necessary at low power

and nan_ishan
i think u r reffering to last 2 points given there
again that depends upon application and ur requirements
that for "large load" BJT is used
 

My discussion is about general purpose......
Very Basic MOS andBJts......the very basic technology and not their advanced modified variants
 

so you are saying a general purpose bjt is faster than a general purpose mos?
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top