Editing Comparator (section)

===Hysteresis===
A comparator normally changes its output state when the voltage between its inputs crosses through approximately zero volts. Small voltage fluctuations due to noise, always present on the inputs, can cause undesirable rapid changes between the two output states when the input voltage difference is near zero volts. To prevent this output oscillation, a small [[hysteresis]] of a few millivolts is integrated into many modern comparators.<ref>{{cite web |author=Ron Mancini |title=Adding Hysteresis to comparators |url=https://www.edn.com/adding-hysteresis-to-comparators/ |website=EDN |date=May 3, 2001<!--Correct date from https://web.archive.org/web/20050221054157/http://edn.com/article/CA84881.html-->}}</ref> 
For example, the LTC6702,<ref>{{cite web |title=LTC6702 - Tiny Micropower, Low Voltage Dual Comparators |publisher=Linear Technology |url=http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1154,C1004,C1012,P38930 |archive-url=https://web.archive.org/web/20110102140904/http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1154,C1004,C1012,P38930 |archive-date=2011-01-02 |url-status=dead}}</ref> MAX9021,<ref>{{cite web |title=MAX9021, MAX9022, MAX9024: Micropower, Ultra-Small, Single/Dual/Quad Single-Supply Comparators |publisher=Maxim Integrated Products |url=http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2411/t/al |archive-url=https://web.archive.org/web/20090330140406/http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2411/t/al |archive-date=2009-03-30 |url-status=dead}}</ref> and MAX9031,<ref>{{cite web |title=MAX9030, MAX9031, MAX9032, MAX9034: Low-Cost, Ultra-Small, Single/Dual/Quad Single-Supply Comparators |publisher=Maxim Integrated Products |url=http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2363/t/al |archive-url=https://web.archive.org/web/20090331134510/http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2363/t/al |archive-date=2009-03-31 |url-status=dead}}</ref> have internal hysteresis desensitizing them from input noise. In place of one switching point, hysteresis introduces two: one for rising voltages, and one for falling voltages. The difference between the higher-level trip value (VTRIP+) and the lower-level trip value (VTRIP-) equals the hysteresis voltage (VHYST).

If the comparator does not have internal hysteresis or if the input noise is greater than the internal hysteresis then an external hysteresis network can be built using positive feedback from the output to the non-inverting input of the comparator. The resulting [[Schmitt trigger]] circuit gives additional noise immunity and a cleaner output signal. Some comparators such as LMP7300,<ref>{{cite web |title=LMP7300 - Micropower Precision Comparator and Precision Reference with Adjustable Hysteresis from the PowerWise® Family |publisher=National Semiconductor Corporation |url=http://www.national.com/pf/LM/LMP7300.html |url-status=dead |archive-date=2009-05-03 |archive-url=https://web.archive.org/web/20090503133351/http://www.national.com/pf/LM/LMP7300.html}}</ref> LTC1540,<ref name=LTC1540/> MAX931,<ref>{{cite web |title=MAX931, MAX932, MAX933, MAX934: Ultra-Low-Power, Low-Cost Comparators with 2% Reference |publisher=Maxim Integrated Products |url=http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1219 |url-status=dead |archive-url=https://web.archive.org/web/20100330215239/http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1219 |archive-date=2010-03-30}}</ref> MAX971,<ref name=qv_pk/1279>{{cite web |title=MAX971, MAX972, MAX973, MAX974, MAX981, MAX982, MAX983, MAX984: Ultra-Low-Power, Open-Drain, Single/Dual-Supply Comparators |publisher=Maxim Integrated Products |url=http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1279/t/al |url-status=dead |archive-url=https://web.archive.org/web/20090330185135/http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1279/t/al |archive-date=2009-03-30}}</ref> and ADCMP341,<ref>{{cite web |title=ADCMP341: Dual 0.275% Comparator and Reference with Programmable Hysteresis |publisher=Analog Devices, Inc. |url=http://www.analog.com/en/power-management/battery-management/adcmp341/products/product.html |archive-url=https://web.archive.org/web/20090815095219/http://www.analog.com/en/power-management/battery-management/adcmp341/products/product.html |archive-date=2009-08-15 |url-status=dead}}</ref> also provide the hysteresis control through a separate hysteresis pin. These comparators make it possible to add a programmable hysteresis without feedback or complicated equations. Using a dedicated hysteresis pin is also convenient if the source impedance is high since the inputs are isolated from the hysteresis network.<ref>{{cite web |id=AN3616 |publisher=Maxim Integrated Products |url=http://www.maxim-ic.com/appnotes.cfm/an_pk/3616/ |title=Adding Extra Hysteresis to Comparators |url-status=dead |archive-url=https://web.archive.org/web/20080509160549/http://www.maxim-ic.com/appnotes.cfm/an_pk/3616/ |archive-date=2008-05-09}}</ref> When hysteresis is added then a comparator cannot resolve signals within the hysteresis band.