bias for high gain opamp

[rajblr]

Hi every one i am designing a BGR for low power specifications, which uses a high gain opamp. I am not so sure how to design a BIAS circuit for opamp to generate a current of 3uA.SO if any one can give me details or design method how to design a bias ckt it will be a great help............


TIA
raags

 

[safwatonline]

u can use the Vbg/R current to bias it , but u will nedd some start up circuit

 

[rajblr]

hi can you just eloborate vbg/r means.........

 

[safwatonline]

Ok , i now think Vbg/R is not a good choice as u will need a buffer, so maybe the better choice is to use a constant gm current
for the bias , but here u will also need a start up circuit.
refer to razavi for more details on the constant gm current