#### dkace

##### Full Member level 6

I want to design a a relatively simple Bandgap reference in CMOS technology. I went through all the literature I could find - Razavi included- but I still have some unsolved issues:

1. It is mathematically proved that Vref=Vout of the OPAMP. I have seen topologies that Vref is the left input of the OPAMP. This contradicts the basic equation that wants TC=0 : Vref=Vbe + Vt Ln n* (1+R2/R3). Any idea?

2. Somebody has to explain me the issue with the OPAMP; We use the OPAMP to maintane equal inputs ( V+=V-) . Then what is the output of the OPAMP and how it corrects any small difference?

3. Second diode has a n - times larger area than first. What is the effect on the current? Which resistor is used to put the current same as reference current? Resostors are teperature dependent. What happens with them in this cell?

I would appreciate if you can back up your answer with maths or references. I am still working on the circuits equations - but I am still a bit rusty with design.

Thanks,

D.