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reducing power in bandgap reference circuit

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hi every one , i am designinig a BGR for sub-1-v range and low power. I have no clue how to choose the required collector current to drive the PNP device in PTAT loop. Also if anyone can tell me how do i choose the reference current to start with, it will be of great use for me.

TIA
raags
 

I use 200nA for 30 bjt transistors in parallel (ratio 1:30).
That's OK!
 

Hi Fom,

Wowsa! Does that mean you have 200nA for each bjt, or 200nA total for all 30?
If the latter, that means 6.7nA each!!!

Mind if I ask how much variation you see in the bangap voltage output?

thanks!
 

Yes 6.7nA for each bjt.
Bandgap need for comparator.
Deviation with comparator offset about 90mV. But we use trimming during CP test.
 

Yes 6.7nA for each bjt.
Bandgap need for comparator.
Deviation with comparator offset about 90mV. But we use trimming during CP test.
 

Hi, choose reference current you need according to its application. So that's ok for Fom to choose 200nA if deviation is not so much cared.
 

normally choose 1uA or 0.5uA for each branch.but you should also trade off the ground noise and power comsumption.
and BJT may choose 1:8 or 1:24 to form common centrid

if the bias current of bjt is too small. the beta of bjt will decrease drasticly.
 

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