PSRR in OTA

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adeineira

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Moved from ANALOG to ANALOG IC section
Dear all,

i want to ask about the psrr for the ota. how to improved the ota psrr.. i get -20dB in 1k


Just wonder anyone have similar experience and can share with me your thoughts.


 

DC PSRR wants more L or cascodes in the guts. But part of PSRR is also "injection pathways". Miller comp in rail-source-connected devices is good layout economics ("C multiplier") but a real bad degrader of "-that- rail PSRR" as any jerk of ourput-vs-rail Vgs applies big initial gain to the supply "input port" perturbation (leaving it to the feedback gain to correct, as far as it's able). Miller comp has no impact on DC PSRR but ruins HF PSRR (and possibly PM) unless you get the zero resistor exactly right.
And no saying that there is a single, tight "right" against PVTL....
 

Hi @adeineira
What is the DC gain of your amplifier? Usually, the PSRR approximately equal to your amplifier gain but with "-" notation...
I think that here is 2 main issues:
1. Differential pair current source is ideal, so whatever variation you have on VDD2 is directly translated to your diff pair. Replacing ideal current source with a real current mirror should help;
2. As @dick_freebird mentioned above, cascoding your current mirrors might be a good solution too.

Hopefully, that helps.
 

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