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A comparator is a device designed detect whether the voltage at one input is higher or lower than the voltage at the other input. Any little difference in the voltage between the comparator
inputs will make the output to to saturation
(and sometimes there cna be some hysteresis in the
state change region). So you can think the
comparator to be in the outptu side a strict
two level output device (1 or 0 on logic world).
Operational amplifier is a device designed to
amplify the voltage difference between the two
inputs. So the operational amplifier will
amplify that voltage difference to the output
by the amplification factor of the opamp IC
(in order of thousands or tens of thousands typically) unless feedback electronics is added
to change the amplification factor to some
lower value. So operational amplifier is true
amplifier with analogue output.
An operational amplifier if used without
any extra feedback operated quite similarly
compared to a comparator, but not in exactly
same way in the transfer region (when those
input voltages are very near each other).
In some circuit design this difference matters,
in other it does not.
But question is, for small difference between the 2 input, is the comparator still a strict 2 level output device?
I think that OTA has high output resistant and opamp has low output resistant
Comparator is a nonlinear circuit, it may care more resolution , but opamp should care for linearity, and opamp are used in feedback loop so we also need to pay more attention to stability in opamp design
Actually there will be different kinds of amplifiers like for those whose output voltage is a function of the input voltage, out put current - as a function of the input current...
they can be named in short hand notation as:
1.)VCVS--voltage controlled voltage source
2.)CCVS
3.)CCVS
4.)CCCS
OTA is an op-amp-like device (operational transconductance amplifier, or OTA) exemplified by the LM13600, a dual amplifier in a 16-pin DIP. It has inverting and noninverting inputs, and an output, like a a normal op-amp, but it is a very different device, and cannot be used like a voltage op-amp. Its applications are specialized, even more so than those of the Norton op-amp, which at least could be persuaded to do the things a normal op-amp does. The OTA is frequently used as an open-loop amplifier. Its gain is not high, and it is not useful in most of the familiar feedback circuits.
The idea of the OTA is to provide a transconductance amplifier, whose input is the differential voltage between its inputs, which are the bases of the transistors of a standard differential amplifier, and whose output is a current proportional to the differential voltage. The transconductance is the ratio of the output current to the input voltage, denoted by gm. The transconductance of an OTA is proportional to the bias current IABC established by an external resistor. At a bias current of 500 μA, the gm of the LM13600 is typically 9.6 mS, but can vary from 6.7 mS to 13.0 mS.
And a comparator is which compares the input with a standard value and give the output accordingly. It is the main device as a state of transfer from analog to digital devices.
An opamp operating in it's saturation regions can also be visulaised as a comparator, but it's functionality is not a perfect one. As you proceed learning op amps you will come across some better circuits for comparators especially the schmitt inverter being used as a comparator.
In that case, how do i know whether my circuit is linear or not? Is it shown by conducting a DC analysis and see if there is a straight line pass the origin when i ramp the input voltage?
If i want something to do comparation for an ADC, and, if say, i can achieve the resolution requirement using an opamp, are there other factors that require me to use a comparator instead? Read somewhere that a comparator uses less power compared to an opamp but i dont see why this is necessary so.
Yes, the way to check whether or not the circuit is in linear region, you can do a DC analysis, however, it's not necessary for the line pass origin since offset exist.
Usually, comparator is a dynamic circuit, so it consume less power.
OTA is current output with high output resistance, Op-amp is voltage output with low output resistance, which can drive resistive load, or high output for capative load. Besides, OTA has relatively higher distortion at large signal and Op-amp has low distortion due to negative feedback.
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