about Bandgap op connect problem

[super]

Dear all:
I design Low voltage Bandgap, use OP feedback type.
My question is , OP+ in connect to R/R ratio terminal
or connect only one R terminal ?
I connect OP+ to R/R ratio or Only one R
terminal , It will work well from simulation.
So I don't know which one is correct.

Thanks .

 

[suria3]

When you derive the Vref output equation, you should be able to find out which is the actual resistor ratio to be. If you are saying not sure on the connection, then there must be something wrong with your equation. Revise again your output Vref equation then i believe you should be able to fix the problem.

 

[jcpu]

Please perform AC anaysis,
one configuration gives you ngative feedback --> stable operation,
the other doesn't.

have fun

 

[dodoro]

Dear all:
I design Low voltage Bandgap, use OP feedback type.
My question is , OP+ in connect to R/R ratio terminal
or connect only one R terminal ?
I connect OP+ to R/R ratio or Only one R
terminal , It will work well from simulation.
So I don't know which one is correct.

Thanks .

The rule is that your negative feedback factor must larger than you positive feedback factor so that you have a stable system. please refer to Razavi's for detail.

 

[satyasiva]

yes. u should get more negative feedback than positive feedback such that system is stable.

 

[dodoro]

i am surprised that i registed this morning,
that the time displayed is 2005. it is a true funny.

 

[super]

Sorry , I still confused.
I refer Razavi's book it show OP+ is connect to One R side , but in my simulation need to connect to R/R ratio side.
I attach my schematic, and label VP , VN .
And please tell me my schematic label is right ?

thanks.[/youtube]

 

[bkat]

yes. u should get more negative feedback than positive feedback such that system is stable.

I agree about that

you should analysis the small signal model for more information.

 

[satyasiva]

i think ur circuit is ok.

 

[super]

Dear all:
Thank you for your suggestion. I have fixed it.
Then I have another question.
I research article about stability test method.And there are many
method I have try it all,but I don't know which one is true.
So I attach my schematic .
I plot VPP gain/phase , the phase margin is 56 degree, it's stable.
please check it for me the method is right ?

Thanks.