how to improve the TC in the bandgap voltage

[CISSE]

my AMP's loop gain is 13K,phase margin is 65,bandwidth is 13M,offset voltage is 60uV,but the TC is poor,about 35ppm/k.So,any suggestion about improvement?

 

[transbrother]

Could you kindly be a little bit more specific?
Are you talking about your amp's TC (i.e. Vout Vs T) or your Bandgap's TC? If it is your bandgap, I am assuming you have designed it to be 0 TC at Room temp. And, so I am assuming (again) that the 35 ppm/K is the max temp deviation that you see in the Vbg Vs. T.

If this is the case, check to see your Ptat current is indeed a Ptat. That is, if it linear and doesnt have any slight "bowing" that makes it an obviously non-linear fuction w.r.t to T; and try to improve upon it.
If you are using ideal resistors, with the best PTAT current that you can possibly generate, and you get rid of any temperature dependent offset of your amp and you still get a poor TC, you should probably switch to a temp-compensated BG.

 

[iamxo]

the opamp in the bandgap circuit just fixes two voltages the same , it will have little effect on the TC of output voltage.

so, I think the large TC comes from your res ratio, it is no well setted. the ratio of the res have large effect of TC.

 

[CISSE]

thanks,transbrother and iamxo.
transbrother:what's w.r.t?
iamxo:how can i get the good ratio?

 

[transbrother]

w.r.t = with respect to

sorry for the abbreviation

 

[CISSE]

the Ptat current i've checked is linear.
what's the meaning of temp-compensated BG?

 

[transbrother]

I meant curvature corrected bandgap....not temp compensated. sorry about that; I was in a hurry when i wrote the reply

-Did you take a dV/DT of the Ptat current and make sure you do not get any second order effects?

-Did you make the resistors ideal and see if there is a difference in the bandgap TC?

-Is your opamp having a temperature dependent static offset? What happens to the gain of the opamp
as temperature is varied?

 

[CISSE]

thanks,transbrother:
i will check them in detail.
i've posted the message to you in the forum,please check it.

 

[kidman561]

The good ratio of the res have large effect of TC.

 

[CISSE]

i just know that the ratio can make the 0 tc at about 300K,i dont know other effect，please tell me in detail

 

[bharatsmile2007]

hi

iam designing a BGR.I need to get the Temperature coefficents for the resistors used in BGR.

Where shall i find the TC values for TSMC 0.18um technology?

Thanks

 

[ytliang]

my AMP's loop gain is 13K,phase margin is 65,bandwidth is 13M,offset voltage is 60uV,but the TC is poor,about 35ppm/k.So,any suggestion about improvement?

your op-amp has little to no effects on the TC of your bandgap reference.
Also, 35ppm/k is good enough already as far as I know. Unless you are talking about the curvature correction design, which might take 35ppm/k as poor performance.