Editing Comparator (section)

==Differential voltage==
[[File:Opamp105.gif|thumb|upright=1.15|Illustration of how a comparator works]]
The differential voltages must stay within the limits specified by the manufacturer. Early integrated comparators, like the LM111 family, and certain high-speed comparators like the LM119 family, require differential voltage ranges substantially lower than the power-supply voltages (±15&nbsp;V vs. 36&nbsp;V).<ref>{{cite web |url=http://www.ti.com/lit/ds/symlink/lm111.pdf |title=LM111, LM211, LM311 Differential Comparators |publisher=Texas Instruments |date=August 2003 |access-date=2014-07-02}}</ref> ''Rail-to-rail'' comparators allow any differential voltages within the power-supply range. When powered from a bipolar (dual rail) supply, 
 
: <math>V_{S-} \le V_+, V_- \le V_{S+},</math>

or when powered from an unipolar [[Transistor-transistor logic|TTL]]/[[CMOS]] power supply,

: <math>0 \le V_+, V_- \le V_\text{cc}</math>.

Specific rail-to-rail comparators with [[bipolar junction transistor#PNP|p–n–p]] input transistors, like the LM139 family, allow the input potential to drop 0.3&nbsp;volts ''below'' the negative supply rail, but do not allow it to rise above the positive rail.<ref>{{cite web |url=http://www.ti.com/lit/ds/symlink/lm139.pdf |title=LM339B, LM2901B, LM339, LM239, LM139, LM2901 Quad Differential Comparators |publisher=Texas Instruments |date=August 2012 |access-date=2014-07-02}}</ref> Specific ultra-fast comparators, like the LMH7322, allow the input signal to swing below the negative rail ''and'' above the positive rail, although by a narrow margin of only 0.2&nbsp;V.<ref>{{cite web |url=http://www.ti.com/lit/ds/symlink/lmh7322.pdf |title=LMH7322 Dual 700 ps High Speed Comparator with RSPECL Outputs |publisher=Texas Instruments |date=March 2013 |access-date=2014-07-02}}</ref> Differential input voltage (the voltage between two inputs) of a modern rail-to-rail comparator is usually limited only by the full swing of power supply.