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comparator compared with amplifier?

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liuyonggen_1

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Could you tell me why two or three-stage comparator do not need miller capacitor to stablize the system??

In my opinion, the difference between the two input voltages is small enough, the comparator is just an amplifier, right??

thank you for your help!
 

the outpput of comparator circuit is binary signal based on the comparison, so it needn't.
 

Because the comparator work in nolinear region,it only need to tell the high olow level ,the opamp work in linear region ,so comp don't need capacitor to stablize ,opamp need!
 

Comparator is open loop system and no question arises for stability. Most of the amplifiers are used in negative fedback in the application, where (beta, the feedback factor is finite) , therefore stability is a concern and we need to do frequency compensation by adding miller cap.
 

liuyonggen_1 said:
Could you tell me why two or three-stage comparator do not need miller capacitor to stablize the system??

In my opinion, the difference between the two input voltages is small enough, the comparator is just an amplifier, right??

thank you for your help!
Click to expand...

The key point is that the comparator works in open loop, and amplifier is used in close loop. Sometimes, the two stage amplifier can be used for a comparator in open loop.
 

some comparators need hysterises but some doesn't, why?? depend on the voltage gain or resolution??
 

hi friend

The compare operation if performed on two inputs . one is the analog input and second is the ref. input. If the analog input is greater than the ref input your o/p will become one(high). else zero(low). most ADCs 0804,0809,0808 will use the comparator as an input to the ADC to set or reset the MSB bit in the SAR resister.
I dont think it will not amp_ any thing
 

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