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Hello, I am designing a bandgap on gf180, however,...
# analog-design
j
Hello, I am designing a bandgap on gf180, however, I wanted a smaller TC, so I used the topology that includes an opam, however, I have made several adjustments and I can't see the curvature, does anyone know what this could be? (the opam has a gain of 52db)
h
The BG voltage is dropping vs. temperature, this means that the negative TC component is too large. You need to tweak the relative scaling of the positive TC component (coming from the deltaVBE) and the negative TC component (coming from VBE).
j
Do you mean modifying the CTAT and PTAT?
l
try to print your screen instead of taking actual pictures of it. this way it is easier for us to analyse it
You can also plot the derivative of the output voltage and make parametric simulations. You can do that by change the values of the resistors. Try changing the second resistor until you find the best design. Remember that the best simulation results aren't always true. And you need to assure your circuit is stable.
h
@Juan Andres yes, you need more PTAT. Make R2 larger.
j
I understand, but this is already a more manual setting, right? A question that is asked when, well, the design works well in a typical corner, and when testing in others, the TC varies a lot?
h
Just the typical variation of a BG, which is on the order of 1-3%. If you want a precise voltage then you need to trim it. In any case, this is the typical design procedure: Get rid of the linear TC for nominal process, and live with the resulting variation.
j
What do you mean by removing the linear tc?
h
Tweak the CTAT and PTAT until you see a “hump” vs. temperature, means just a curvature of 2nd order. In the picture above you have a TC1 (pretty dominant) and a TC2 (hard to see since TC1 is so large).
j
Yes that I can fix but now I have error with corner
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