Generally, large L or cascode structure can improve PSRR. Because both of them lead to higher output resistance, which makes drain current more stable when there is Vds variation.
due to larger L the lamda effect will reduce hecnce the output resistance will increase and the circuit will be more robust for the any noise r any variation of VDD hence greater PSRR ..
hope this helps.
In my opinion, bandgap psrr is mainly depended on the structure which you choose. Secondly, the op amp is also important, refine its propery ,you can acquire more high psrr for the bandgap.
Can I use a voltage regulator before a bandgap to further inprove PSRR? In this case, it create a loops between bandgap and voltage regulator, where bandgap supply reference voltage to regulator. Anyone have experience in this?
Large L means
1. lambda effect lower
2. o/p res Rds of tr is higher
Basically u need higher resistance. U can do by decreasing W also but the lambda effect gets decreased by big L. So anther adv