Improving Bandgap PSSR

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ccw27

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pssr bandgap

How can I improve the PSSR of the bandgap attached? I am only achieving PSSR of 30 dB.

Thanks
 

bandgap negative pssr

If it is your real schematic, why substrate of PMOS transistors not connected to VDD?
 

In my real schematic it is. This picture was taken from a paper
 

That's wrong! You should connect substrate to VDD. Change it and simulate again. By the way do you simulate PSRR by AC or transient analysis?
And what is your VDD range?
 

It is common low-voltage BG has poor PSRR. You can put a big capacitor at the output node to improve it.
 

Any suggestion for high PSSR bandgap topology? Paper?

Thanks
 

I think this circuit has poor PSRR because of M1+M3+M5 gate capacitor that connected between VDD and negative input of OP amp.
 

I think the output of opamp must be connected to the gate of M1 & M3. Because M2 & M4 are used just for current match (i1 & i2).
 

from which paper did you take the schematics?
 

Here is the paper
 

connect the output of OPA to the gate of M1,M3.Further to improve the PSR of bandgap you can increase the gain of OPA
 

I think M1~M4 need use long channel mos for get good PSRR
 

Do you want to improve PSRR for high frequency or low frequency?
 

less than 10 MHz
 

Can't connect output of OPA to the gate of M1,M3, you would short input to output of OP.
 

you DO not need connect the gate of M1&M3 to node X, just get rid of it and connected to the output of OP. And what about the gate of M2&M4 ? just refer to Razavi's book to find out how to bias the cascode stage.
 

i think your opamp's gain is low.
 

I think this structure is not good, the error amplifier output connect with the cascode PMOS gate, not thegate of M1 and M2 , then the gain will be very low. so i think that the error amplifier output connect with the gate of M1 and the M1 gate can't connect with the drain of M2.
 

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