Need help...A Simple bandgap reference.

[hipichu777]

Hello every one, i'm new here and new to analog IC design.

Here's my first real job.

I need to design a bandgap reference (with startup) whose output is around 1.8v and is independent of temperature (-40 to 105 c) and vdd (2.7 to 3.3v)
using opamp and 8:1 BJT pairs in smic18 and Cadence environmnet.

Circuits shown below.

I know it's not that difficult, but i have been trying this for over a week and has got very limited results (output change greatly over variation of vdd)

Could anyone show me a real circuit that could work that way?

Thank you very much indeed.

 

[leo_o2]

It is a self-biased bandgap.
However, I suggest changing start-up circuit with detecting scheme.

 

[hipichu777]

Thanks for the advice, but right now I just want to make this work, and then improve it with other structure.

 

[rajanarender_suram]

1) the third terminal of the resistors are connected to Vdd. As Vdd changes ur resistance values change. So connect the third terminal to OUTPUT . so that the Vdd change doesn't have the effect on the resistance values

 

[hipichu777]

good idea.

Now I simply changed the resistors to ideal ones. The output is still greatly infulenced by vdd variation.

 

[rajanarender_suram]

i want to see the variation of OUTPUT Vs VDD plot??

1. in the schematic it looks like u shorted the bulk of PMOSes(M5 & M12) to its gate. Check the connection

 

[hipichu777]

Thanks eveybody for the your help

Problem solved!

I used a better opamp and did some other minor changes.