Questions about bandgap: bipolar transistor

[ietc]

questions about bandgap

there are many parameters in the mos devices which can be used to generate reference.
why use the bipolar transistor in the bandgap ?

how about use Temperature coeffecients of resistors in the bandgap ?

thanks in advance.

 

[shiowjyh]

Re: questions about bandgap

Hello,

Please go to this web, there does exist good stuffs for designers...

http://www.circuitsage.com/

Regards,

Ryan

 

[nuiscet]

questions about bandgap

The bipolar transistor has good linearity of dependence on temperature. and the mosfet transistor is unstabe with the temperature changing.

 

[pk3316]

questions about bandgap

for temp independed reference, we need pos and neg temp coefficient. Normally the delta Vbe can provide a very good pos TC, the Vbe can present a neg TC. Even the parasitic pn junction in CMOS process can meet this requirement in common IC works.

 

[limingchou]

questions about bandgap

that is to say
vref=Vbe+kVt
there, Vbe is neg temp and Vt is pos temp coefficient. and the pnp can be implement using the substrate transistor. and it is implemented at the trandition technology.

 

[electronrancher]

questions about bandgap

the mos parameters are not well controlled, so the variation in your reference will be large and it will need a lot of trim to get good precision.

for a ieee paper, it's fun to see how many different references you can make to get your name published. when you're shipping 1,000,000 units/month you are not interested in fun, only yield.

as far as the tempco of the resistors goes - haha you'll have to write the loop equations to figure it out!

no just kidding, if you use all the same resistors the % change is proportional and it washes out for the most part - perhaps moving your inflection point a little bit higher or lower, but that's no big deal. you build one, find the "magic" voltage of that cell and tell your test engineer to trim them all to Vmagic.

 

[huojinsi]

Re: questions about bandgap

According to Vref=KVt+Vbe,Vt has a positive coefficient and Vbe has a negative coefficient,K is resistance ratio.By adjusting resistance ratio can change K value,at last Vref can reach zero coefficient. So u don't care the resistor temperature coefficient under the condition of same type resistor.