How to increase the gain of a comparator?

[menewbie]

Comparator

hi, I need to design this comparator that has a very gain around 2000000. So far, i have 3 stages for the comparator: diff amp with active loads, hysteresis and a CMOS diff amp. But the gain is only around 3000 and I need more than that. How can I increase the gain of the comparator?

 

[jlee]

Re: Comparator

Increasing DC gain can be done by several approaches... it is actually a tradeoff of different spec you have to filled.

In your case, you need another DC gain of about 1k. Probably try cascoded transistors or gain boosting to increase the output resistance of the first stage. Cascoded transistors will increase your DC Gain by gm*ro; Gain boosting will increase your DC gain by A*gm*ro. In both case, the tradeoff will be a smaller output swing on the first stage; fortunately, it is the first gain stage, so a smaller output swing should not hurt.

 

[mpig09]

Re: Comparator

Dear menewbie :

If you only want a very high gain comparator, you can try positive feedback
structure comparator.



mpig09