why is bandgap curve upside-down??

[ddrr]

The characteristic curve of my bandgap is upside-down...(The TC of all the resistors are set to zero)

 

[saro_k_82]

You cant expect to get an answer showing just a plot. There are numerous ways to implement a reference and some circuits yield this.

 

[ddrr]

But my topology is typical...

 

[M.Sansen]

Hi ddrr,
I have met the same problem. It seems that the resistor has an influence on the tempco.

 

[leebluer]

Does 'The TC of all the resistors are set to zero' mean ideal resistor used in the simulation? In my simulation, if negative Tc resistor used, upside curve occurs. If possible, do not change resistor model, but use ideal ones.

 

[pankajdudulwar]

Please check the TC of the resistor and then the gain of opamp. Whether opamp is misbehaving

 

[dick_freebird]

There is no point simulating a bandgap with ideal resistors, unless
your implementation has them available.

 

[checkmate]

The circuit equations show that they are relatively independent of the tempco of R.
Vbg=Vbe + dVbe*R2/R1.
R2/R1 is temperature independent and depends only on its matching.
Differentiate this with T, and you will get the first term which is -ve and non-linear (closely resembling a TlnT relationship), and the 2nd term which is +ve but much more linear. This always give the characteristic bandgap as seen in most textbooks.

You should really be looking at other sources of error, ie how good is the current matching between the 2 bjts. You are using a non-cascoded current mirror, so that will affect the matching of the 2 currents. Does your resistors have any voltage dependence etc. etc.