I am designing Bandgap Bias gen circuit using UMC180 technology. I have following questions.

1. The process has only parasitic PNP BJT.  How to consider variations in base(Nwell) doping ? The foundry provides only one model file for BJT with no variations information.  

2. Which model parameters of BJT can vary due to process variations ? What is the amount of variations in these parameters ?  

3. In all if I want to consider all the type of variations and make sure that the designed circuit works on silicon what all I should consider apart from checking the circuit for all MOS and  Resistance variations given by their model files. ?


-CA