What is the ratio of BJT in BGB ?

[varma_cs012]

Hi chap,

In BGB we will be having two BJTs. Upto now I seen the reatios of BJTs 1:8, 1:24, 1:48.
But most of the circuits we will use 1:24 only. Why it is like that ?

Thank You.
Varma

 

[ken_cn]

Hi Varma,
these ratioes are chosen for centrosymmetric layout consideration.
taking the 1:8 for example, you can layout the 1 in the centre and place the 8 around it to make up a 3*3 centrosymmetric array.
hope it help.

 

[varma_cs012]

Thanks,

I also know that we will choose that ratios for centrosymmetric layout.But my doubt is how we will decide the ratio whether 1:8 or 1:24 or 1:48. In most of the designs 1:24 is used. I want to know why we use that ? Thank You in Advance.

Varma

 

[DenisMark]

See my post for answer:

 

[yibinhsieh]

The bigger ratio of BJT means it can tolerance more offset voltages in the BG circuits. Usually I use 1:8 to save power and area. But the variation in mass production is a little big but can be accepted.