Editing Comparator (section)

==Applications==
{{main|Comparator applications}}
[[File:Calibration Comparator (7504822476).jpg|thumb|right|A precision calibration comparator]]
===Null detectors===
A null detector identifies when a given value is zero. Comparators are ideal for null detection comparison measurements, since they are equivalent to a very high gain amplifier with well-balanced inputs and controlled output limits. The null detector circuit compares two input voltages: an unknown voltage and a reference voltage, usually referred to as v<sub>u</sub> and v<sub>r</sub>. The reference voltage is usually on the non-inverting input (+), while the unknown voltage is usually on the inverting input (&minus;). (A circuit diagram would display the inputs according to their sign with respect to the output when a particular input is greater than the other.)  Unless the inputs are nearly equal (see below), the output is either positive or negative, for example ±12&nbsp;V. In the case of a null detector the aim is to detect when the input voltages are nearly equal, which gives the value of the unknown voltage since the reference voltage is known.

When using a comparator as a null detector, accuracy is limited; an output of zero is given whenever the magnitude of the voltage difference multiplied by the gain of the amplifier is within the voltage limits. For example, if the gain is 10<sup>6</sup>, and the voltage limits are ±6&nbsp;V, then an output of zero will be given if the voltage difference is less than 6&nbsp;μV. One could refer to this as a fundamental uncertainty in the measurement.<ref>{{cite book |title=Electronics and Instrumentation for Scientists |last1=Malmstadt |first1=Howard V. |last2=Enke |first2=Christie G. |last3=Crouch |first3=Stanley R. |publisher=The Benjamin/Cummings Publishing Co |year=1981 |isbn=978-0-8053-6917-5 |pages=[https://archive.org/details/electronicsinstr0000malm/page/108 108–110] |url-access=registration |url=https://archive.org/details/electronicsinstr0000malm}}</ref>

===Zero-crossing detectors===
For this type of detector, a comparator detects each time an [[Alternating Current|AC]] pulse changes polarity. The output of the comparator changes state each time the pulse changes its polarity, that is the output is HI (high) for a positive pulse and LO (low) for a negative pulse squares the input signal.<ref>{{cite book |title=Electronics and Instrumentation for Scientists |last1=Malmstadt |first1=Howard V. |last2=Enke |first2=Christie G. |last3=Crouch |first3=Stanley R. |publisher=The Benjamin/Cummings Publishing Co |year=1981 |page=[https://archive.org/details/electronicsinstr0000malm/page/230 230] |isbn=978-0-8053-6917-5 |url-access=registration |url=https://archive.org/details/electronicsinstr0000malm}}</ref>

===Relaxation oscillator===
A comparator can be used to build a [[relaxation oscillator]]. It uses both positive and negative feedback. The positive feedback is a [[Schmitt trigger]] configuration. Alone, the trigger is a [[bistable multivibrator]]. However, the slow [[negative feedback]] added to the trigger by the RC circuit causes the circuit to oscillate automatically. That is, the addition of the RC circuit turns the hysteretic bistable [[multivibrator]] into an [[astable multivibrator]].<ref>{{cite book |author1=Paul Horowitz |author2=Winfield Hill |title=The Art of Electronics |publisher=Cambridge University Press |edition=2nd |place=Cambridge |year=1989 |pages=284–285}}</ref>

===Level shifter===
[[File:DOV-1X - National Semiconductor LM393N on printed circuit board-9800.jpg|thumb|National Semiconductor LM393]]
This circuit requires only a single comparator with an open-drain output as in the LM393,<ref>{{cite web |title=LM393: Dual differential comparator, commercial grade |publisher=Texas Instrument |url=http://www.ti.com/product/lm393}}</ref> TLV3011,<ref>{{cite web |title=TLV3011: Low-power comparator with reference (open-drain) |publisher=Texas Instrument |url=https://www.ti.com/product/TLV3011}}</ref> or MAX9028.<ref name=qv_pk/4268/> The circuit provides great flexibility in choosing the voltages to be translated by using a suitable pull up voltage. It also allows the translation of bipolar ±5&nbsp;V logic to unipolar 3&nbsp;V logic by using a comparator like the MAX972.<ref name=qv_pk/1279/><ref name="test"/>

===Analog-to-digital converters===
When a comparator performs the function of telling if an input voltage is above or below a given threshold, it is essentially performing a 1-bit [[Quantization (signal processing)|quantization]]. This function is used in nearly all analog to digital converters (such as [[Flash ADC|flash]], pipeline, [[Successive-approximation ADC|successive approximation]], [[delta-sigma modulation]], folding, interpolating, [[Integrating ADC|dual-slope]] and others) in combination with other devices to achieve a multi-bit quantization.<ref>{{cite book |author1=Phillip Allen |author2=Douglas Holberg |title=CMOS Analog Circuit Design |publisher=Oxford University Press |edition=2nd |place=Oxford |year=2002}}</ref>

===Window detectors===
Comparators can also be used as window detectors. In a [[window detector]], a comparator is used to compare two voltages and determine whether a given input voltage is under voltage or over voltage.

===Absolute-value detectors===
Comparators can be used to create absolute-value detectors. In an absolute-value detector, two comparators and a digital logic gate are used to compare the absolute values of two voltages.<ref>{{cite book |last1=Iranmanesh |first1=S. |last2=Rodriguez-Villegas |first2=E. |title=2016 14th IEEE International New Circuits and Systems Conference (NEWCAS) |chapter=CMOS implementation of a low power absolute value comparator circuit |publisher=IEEE Newcas |date=June 2016 |pages=1–4 |doi=10.1109/NEWCAS.2016.7604807 |isbn=978-1-4673-8900-6 |s2cid=10810576}}</ref>