Stages of high speed comparator

[carlson]

Hi, all!
There are ofter 3 stages comparator in the high speed comparator.
They are preamplifer stage,decision stage,output stage.
And I have the 2 questions.
1. What about the specifications for the 3 stages (for example gain et.)?
2. Is there any architechture for decision stage (for example postitive feedback)?
Can the decision stage without positive feedback be used? If yes, what are the specitial specification for it?

Best Regards

 

[jerryzhao]

If the 3 stage, first and second stage use diode-connected load op. the third stage use latch(positive feedback).
The two front end op are low gain high speed.(if the gain high it's speed will be low).
latch's resoution low, speed high, so need preamplifer)

 

[carlson]

Thanks!
And I saw a high speed comparator.
The first stage is resistive load comparator. The second stage use the two diff amp.
And the third stage use the diff amp. But this does not use latch.
why?

 

[jerryzhao]

U can design like that. But if the third stage is high gain(gain too high) it is bandwith will be low. U shoule take care it.
You'd tell your comparator's spec. Such as the speed, resolution.

 

[shake2004]

martin's book can tell you how to do