How to size BJT for BGR design...

[rajblr]

hi every one ,
can anyone tell me how to size the BJT for bandgap reference design. If u have any material it will be of great use for me.

TIA
raags

 

[Blackuni]

Hi,

Please search for voltage reference or BG in this forum there are also some recent post.

But most of them don't discuss about the device sizing in detail especially about BJT and the devices in error amplifier.

so I used to decide device size based on the current which will satisfy your power budget.

Hope this helps!

What is u r design spec? Designing BG for <1 is a tough thing as most of the device will operate in triode /deep triode region.

I posted few questions in this forum but no reply which helped to learn a lot.

Let me know for any more questions i will try 2 answer

Thanks

 

[ipierre]

Please refer to Page 31.

**broken link removed**

 

[rfzheng]

1:8 of 1:24 for easy layout and match,
1:8 is better for pratical use in the engineering

 

[rajblr]

hi Blackuni,
i am designing a BGR to generate a voltage about 0.6volts. I have finalised an architecture which is used for sub-1-v BGR without low Vth transistors and resisitive divide network. But my confusion is that how to size the BGR, like emitter are, base area or else. Also How exactly the temperature depence (PTAT & CTAT) will get cancelled each other with this architecture.

TIA
raags

 

[survivor]

Hi,

Usually, the BJT drawing size provided by foundary is used for design due to modeling accuracy. As for BJT area ratio of the PTAT part, it depend on the offset voltage of the OPA used in bandgap. If you want to have small statistics deviation of your 1.25V output during production, you can choose 1:24 or larger. Or you can try to minimize the offset of the OPA, then 1:8 ratio is OK,too.

Hope it helps