Difference between Differential op amp. and comparator

[kidi3]

What is the Difference between differential op. amp and comparator
I know a comparator only can give me 2 values, supply values.

The differential op. amp amplifies the difference between the inputs.. but should a comparator not do the same then?..
what is the specific difference.

 

[FvM]

OPs have frequency compensated gain needed for stable feedback operation. OPs can be used as a comparator, but switching speed is considerably lower than uncompensated comparators.

 

[rahdirs]

There are several important differences between opamps and comparators.

• Opamps can pull up or down (source or sink current). Many comparators sink current only. They rely on some external means to pull the output positive when the output is off.
• Comparators are usually designed to switch their outputs as fast and hard as possible for the least input differential voltage. Opamps are purposely slowed a bit, and their high frequency response rolled off,to let them stabilize the output voltage at any point in its swing whenever the inputs are brought to a match by negative feedback. If you connect negative feedback around a comparator, it can be expected to oscillate.
• An opamp is also obviously designed to operate in a linear mode, a comparator isn't designed that way, there's no need for it to be so.
• Opamps usually limit output current to some maximum value with an active current measuring circuit, while comparators carry as much current as the the output switch can carry. So the maximum current the output will carry generally varies more with comparators than it does with opamps, unit to unit.
• Opamps are designed to produce an output voltage that is an arbitrary function of input signals, based on the input and feedback networks.Comparators are designed to tell you which input is more positive, as quickly as possible.

 

[FvM]

I agree to most explanation details, except for:

Opamps can pull up or down (source or sink current). Many comparators sink current only. They rely on some external means to pull the output positive when the output is off.

Only moderate speed comparators can have open collector/open drain without detoriating performance. All really fast comparators use push pull outputs, also some newer "micropower" comparators, e.g. TLC3702. Vice versa there are a few open collector OPs like TAA761.