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Criterion for ICMR max in opamp of BGR

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bharatsmile2007

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Hi,

iam designing Bandgap ref in 0.35um,3.3v supply,for the opamp in BGR i designed was , ICMR min is 0.65v and max is 3.14v.

what is the Criterion for ICMR max? (For ICMR min as the input is at around 0.7v,it should be less than 0.7v)

Thanks
 

it depends on the specs you are given and your applications.
 

For a amp used in BGR, that deals with only diode voltages, the ICMR need to only include 0.5 to 0.8., assuming that there is no latch-up when these limits are breached.
 
Thanks for the reply.

So ICMR should be only for the range 0.5 to 0.8 ?

Would you pls explain more on ur comment " assuming that there is no latch-up when these limits are breached " ?

Thanks in again....
 

Working CMR of 0.5 to 0.8 is enough assuming that there is no catastrophe outside it. Eventhough your circuit may not need to function there, these ranges will be exercised during start-up, power-up transients. Common-mode induced latch-up is an old phenomenon that causes output phase reversal when ICMR exceeds limits. I included it just for generality. In your CMOS circuit you don't have to worry about it.
 

bharatsmile2007 said:
Thanks for the reply.

So ICMR should be only for the range 0.5 to 0.8 ?

Would you pls explain more on ur comment " assuming that there is no latch-up when these limits are breached " ?

Thanks in again....
Click to expand...
I think he means as long as your amplifier is functioning with inputs ranging from 0.5v ~ 0.8v, your circuit should be fine. Your ICMR MAX can be as high as you want but no lower than 0.8V. 0.5v~0.8v comes from VBE of the BJT I think.
 
Basic question...

whats the ICMR min & max for the diff pmos?(equation)

Thanks in advance
 

ICMR max=vdd-Vov5-(Vthp1+Vov1)
ICMR min=vss+(vthn3+Vov3)-vthn1
 

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