How to make the op amp faster?

[colinwang]

I've designed a traditional folder cascode op amp. If I want to make the settling time smaller, what's the best way to achieve it?

 

[deepa]

so now u have to increase your bandwidth,so that means you have to reduce the load capacitance or load resisitance or both.to reduce the capacitance make the transistors smaller ,but the ro of transistor is directly proportional to the length of the transistor.
else you can increase the bias currents to increase the bandwidth

 

[colinwang]

Thank you very much! But this will make the phase margin rather bad. If I use the miller capacitor to compensate, then the unity gain bandwith will become smaller than before. So how to extend the bandwidth and also have a good phase margin?

Regards!

 

[deepa]

well now you have twitch the sizes and currents of the transistors until u reach ur specifications.hope you don have a constraint on power ?
now since you know the factors affecting the bandwidth either try to achive one of the specs and then twitch the circuit to meet the other

 

[okguy]

If you really need high speed, decrease your gain and and an extra stage.
The drawback is that it burns more power power !!!