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OPamp and comparators' design

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Templar

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i have a question here...

isn't a comparator just a bunch of cascaded amplifiers?

I've made a comparator formed of cascaded common src stages, with an input differential stage , with single o/p. and it's working just fine, producing a perfect square wave at the o/p when the differential i/p is in range of 100s of microvolts...

so, what's the difference between this comparator and an opamp like 741, for instance?

i think that 741 or other opamps are nothing but comparators if used in open loop configuration.

i have another question, can my simple multistage amplifiers comparator act as a gain-controlled amplifier with -ve fb configurations like the various opamp circuits :?:

thanks
 

I think, it is just a bunch of cascaded amplifiers, but without internal compensation capacitor, thus , the comparators slew rate is much higher and it is less stable
 

Comparator input impedance

1st. Thanks both
2nd. I've found in your posted link PIXEL that comparators have a lower i/p impedance than that of opamps when the latter are used in -ve FB configs.

Well, can this be fixed if a large resistor is placed at the i/p of the comparator, or, it's not that simple ?
 

opamp has negative feedback for stability and comparator has positive feedback
 

There is some good information on this in the below link:
 

comparator has pre-opamp and latch which operated as positive feedback.choose pre-opamp cuz you want to minimize offset,and it has not fb or compensation,so it works faster than opamp.that depands on ft of input transisitor
 

thanks for the link ipsc
 

they are different. of course u can have a bunch of cascaded amps as comparator but that is not efficient in terms of power & area. that is why comparator design is a specialization like opamap. there is no compensation in comp . and it generally functions in openloop while almost all of the amps work in closed loop. slewrate shd be more in comp. the 3db bw is higher for the same config(say 2 stage comp. or amp) because "no compensation" is the answer. so slew rate shd be better to process higher bw signals.

also my gain has to great for comparator so that my resolution(vmin) will be less and ultimately by switching time will also be less. these are some of the aspects for comaprator deisgn
 

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