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Design >> Analog Design >> Designing of Bandgap Circuit pointers
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Message started by avlsi on Sep 25^th, 2010, 6:50am

Title: Designing of Bandgap Circuit pointers
Post by avlsi on Sep 25^th, 2010, 6:50am

Hi all,
I donot know whether anyone encountered the problem I am facing.

When designing a current mode bandgap for low voltage like 1.2 V VDD, I have done the basic design with ideal current sources, ideal resistors, ideal VCVS and ideal CCCS(as mosfets), actual BJTs' . But the value of the resistors from hand calculations are not at all the final values of the design (to get a bell curve with peak at 27 Deg C).

Please suggest any good reference for bandgap designs as i feel the hand caculations may be an issue.

Thanks in advance

Title: Re: Designing of Bandgap Circuit pointers
Post by RobG on Sep 27^th, 2010, 4:19pm

You are doing the right thing in not just believe what the model shows. If you want a bg ref to work you need to understand what is not making work ideally.

Generally the problem is current density being too large so it no longer behaves as an ideal device -- usually from the IR drop in the base resistance. You should go to the model and zero out the non-ideal components (Rb, knee current, beta, etc). Also check the equations that your model uses. There are lots of temp dependencies in there: XTI, EG, temp dependence of EG, etc... make sure you hand calc includes these.

Title: Re: Designing of Bandgap Circuit pointers
Post by love_analog on Oct 11^th, 2010, 6:17am

Um...what is a current mode bandgap. Can you please post schematics so we can do a theoretical calculation. Typically your final resistor values will be close to the theoretical values, though not exact (to get the best tempco)