bandgap vref curve is downward concavity or upward concavity?

[williamy]

help: bandgap vref curve is downward concavity or upward concavity? Someone tell me if curve is upward concavity, it is error, why?
Thanks!

 

[sevak112]

My bandgap result go up from 0 to 20 C and then after its go downward.Its identical to one paper i saw online.As temperature increase thresold voltage increase and that's why reference voltage goes down.I have no idea why its go up in starting.

 

[saiaditya]

I guess it could be either way. It depends on how the compensation is being done. Assuming first order compensation vref=k1*vbe + k2*delta_vbe. So depending on how the constants are set, i guess vref could be upward or downward concave.

 

[dick_freebird]

Upward is not the norm, but it's not necessarily an "error".
The right set of component curvatures could give you a
"non-classical" profile. However the real question always
is, are your models really accurate enough for voltage
reference design?

Modeling dudes will pretend they did a good job until
you show them data. Of course if you can't show the
data then you've got nothing.

 

[williamy]

Upward is not the norm, but it's not necessarily an "error".
The right set of component curvatures could give you a
"non-classical" profile. However the real question always
is, are your models really accurate enough for voltage
reference design?
Modeling dudes will pretend they did a good job until
you show them data. Of course if you can't show the
data then you've got nothing.

Hi, dick_freebird:
the model I used is relatively accurate. More strangely, in some case, i can get upward and downward curve by adjust some paramenters.
you say upward is not the norm, can you explain more? Thanks!

---------- Post added at 09:45 ---------- Previous post was at 09:42 ----------

I use same structure, the temperature of Vbe and delta(Vbe) seem both right.

 

[IADanilov]

williamy, could you show your circuit and Vref curve?

 

[williamy]

I do not know how to upload picture. the circuit of bandgap is common used, about 1.2V vref out, and no use opa.
I find the Vbe change little with temperature, it seem not right. I wonder it is the reason of model.