https://hades.mech.northwestern.edu//index.php?action=history&feed=atom&title=ComparatorsComparators - Revision history2026-05-17T07:00:40ZRevision history for this page on the wikiMediaWiki 1.43.8https://hades.mech.northwestern.edu//index.php?title=Comparators&diff=9161&oldid=prevDanJohnson at 14:53, 9 December 20082008-12-09T14:53:31Z<p></p>
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</table>DanJohnsonhttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=9159&oldid=prevDanJohnson at 14:37, 9 December 20082008-12-09T14:37:31Z<p></p>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>In order to implement this electronically, we can use a comparator as shown in the circuit diagram below. This circuit creates a noninverting comparator with hysteresis.[[Image:hysteresiscomparatorcircuit.jpg]]</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>In order to implement this electronically, we can use a comparator as shown in the circuit diagram below. This circuit creates a noninverting comparator with hysteresis.[[Image:hysteresiscomparatorcircuit.jpg]]</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><br /></td>
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</table>DanJohnsonhttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=9157&oldid=prevDanJohnson at 14:32, 9 December 20082008-12-09T14:32:10Z<p></p>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Comparators with Hysteresis==</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>You may run into a problem with implementing a comparator circuit as described above if your input signal has any noise in it, especially in the ''anything goes'' region where the two inputs (inverting and non-inverting) are nearly equal. The noise in the signal could cause the comparator output to flicker, as shown on the right. [[image:comparatorflicker.jpg|right]]</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>You may run into a problem with implementing a comparator circuit as described above if your input signal has any noise in it, especially in the ''anything goes'' region where the two inputs (inverting and non-inverting) are nearly equal. The noise in the signal could cause the comparator output to flicker, as shown on the right. <ins style="font-weight: bold; text-decoration: none;">In order to eliminate this flickering behavior, a hysteresis band can be added to the comparator.</ins>[[image:comparatorflicker.jpg|right]]<ins style="font-weight: bold; text-decoration: none;"> </ins></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>A comparator with hysteresis has two important thresholds: upper and lower. Unlike a simple comparator, however, the output of the comparator doesn't depend solely on whether the input is above or below one of these thresholds. It depends on both the current state of the output '''and''' the current value of the input. If the output is high, it will stay high until the input voltage drops below the lower threshold. If the output is low, it will stay low until the input voltage rises above the upper threshold.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>A common example of a hysteresis band is the thermostat in your house. If the system is cooling, it will cool the house down to a given temperature and then turn off. It will not turn on until the room has heated up a certain amount again, otherwise it would be turning off and on quite rapidly. This difference in temperatures allowed before the cooling turns back on is a hysteresis band. If the system is currently on, the ''high'' output, it will stay on until the temperature is below a lower threshold. If the system is off, the ''low'' output, it will stay off until the temperature is above an upper threshold.</div></td>
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</table>DanJohnsonhttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=9154&oldid=prevDanJohnson at 14:17, 9 December 20082008-12-09T14:17:07Z<p></p>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* LM311 allows its inputs to range independently anywhere from +15 to -15, without damage. Many comparators are much more finicky. For many, the range of the inputs must not exceed the range between the power supply rails (e.g. 0 to +5)</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>* LM311 allows its inputs to range independently anywhere from +15 to -15, without damage. Many comparators are much more finicky. For many, the range of the inputs must not exceed the range between the power supply rails (e.g. 0 to +5)</div></td>
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</table>DanJohnsonhttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=4866&oldid=prevLIMS at 13:14, 12 January 20072007-01-12T13:14:31Z<p></p>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Comparators have two inputs, called inverting and non-inverting inputs, and labeled simply - and + on a circuit diagram. We will call the potential at these inputs V<sub>--</sub> and V<sub>+</sub>. Don't confuse these inputs with power supply connections! See figure 1: inputs on the side, power on the top and bottom. Often power is not even shown, but if you neglect to provide it the chip won't work. </div></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Comparators have two inputs, called inverting and non-inverting inputs, and labeled simply - and + on a circuit diagram. We will call the potential at these inputs V<sub>--</sub> and V<sub>+</sub>. Don't confuse these inputs with power supply connections! See figure 1: inputs on the side, power on the top and bottom. Often power is not even shown, but if you neglect to provide it the chip won't work. </div></td>
</tr>
<tr>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
</tr>
<tr>
<td class="diff-marker" data-marker="−"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The output of a comparator is logic high (+5V) if V<sub>+</sub> > V<sub>--</sub> and low (0V) if V<sub>+</sub> < V<sub>--</sub> . If they are within 1mV of equal, anything goes.</div></td>
<td class="diff-marker" data-marker="+"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The output of a comparator is logic high (+5V) if V<sub>+</sub> > V<sub>--</sub> and low (0V) if V<sub>+</sub> < V<sub>--</sub> . If they are within<ins style="font-weight: bold; text-decoration: none;"> about</ins> 1mV of equal, anything goes.</div></td>
</tr>
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<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
</tr>
<tr>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Comparators are much like opamps, but opamps intend to have a continuous output Vout = G(V<sub>+</sub> - V<sub>--</sub>), where comparators intend to saturate, that is, always to have a full positive or zero output. </div></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Comparators are much like opamps, but opamps intend to have a continuous output Vout = G(V<sub>+</sub> - V<sub>--</sub>), where comparators intend to saturate, that is, always to have a full positive or zero output. </div></td>
</tr>
</table>LIMShttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=4865&oldid=prevLIMS at 13:13, 12 January 20072007-01-12T13:13:57Z<p></p>
<table style="background-color: #fff; color: #202122;" data-mw="interface">
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<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><br></div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<tr>
<td class="diff-marker" data-marker="−"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The LM311P, like most comparators, is open-collector. That means it is capable of grounding its output to indicate logic low, but that's all it can do. It cannot drive its output high (to +5V for instance). All it can do to indicate logic high output is NOT ground its output. It's your job to pull the output high (with a "pull up resistor") and the LM311P will pull it low when it needs to. <del style="font-weight: bold; text-decoration: none;">[[image:lm311p.jpg|right]]</del></div></td>
<td class="diff-marker" data-marker="+"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">[[image:lm311p.jpg|right]] </ins>The LM311P, like most comparators, is open-collector. That means it is capable of grounding its output to indicate logic low, but that's all it can do. It cannot drive its output high (to +5V for instance). All it can do to indicate logic high output is NOT ground its output. It's your job to pull the output high (with a "pull up resistor") and the LM311P will pull it low when it needs to. </div></td>
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<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
</tr>
<tr>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Why don't they include a pull up resistor inside? Sometimes they do. However, the open collector output allows you to pull it up to other voltages besides +5 at your whim, for instance to +3 or +24, or to drive an LED (and its limiting resisitor.) You can also arrange several comparators "wired OR", meaning the outputs of several comparators are connected and if any of them pulls the output to ground, it dominates all the others. You couldn't do that if one was pulling the output high and another pulling it low.</div></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Why don't they include a pull up resistor inside? Sometimes they do. However, the open collector output allows you to pull it up to other voltages besides +5 at your whim, for instance to +3 or +24, or to drive an LED (and its limiting resisitor.) You can also arrange several comparators "wired OR", meaning the outputs of several comparators are connected and if any of them pulls the output to ground, it dominates all the others. You couldn't do that if one was pulling the output high and another pulling it low.</div></td>
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</table>LIMShttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=4864&oldid=prevLIMS at 13:13, 12 January 20072007-01-12T13:13:23Z<p></p>
<table style="background-color: #fff; color: #202122;" data-mw="interface">
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><br></div></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><br></div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<tr>
<td class="diff-marker" data-marker="−"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has infinite input impedance. That means that it observes the voltage at its input while allowing no current to flow. Real comparators are pretty close to this ideal, swallowing only a few nA. This is very useful when you have a high impedance signal (having very little current available) such as a phototransistor.</div></td>
<td class="diff-marker" data-marker="+"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">[[image:light.jpg|right]] </ins>An ideal comparator, like an ideal opamp, has infinite input impedance. That means that it observes the voltage at its input while allowing no current to flow. Real comparators are pretty close to this ideal, swallowing only a few nA. This is very useful when you have a high impedance signal (having very little current available) such as a phototransistor.</div></td>
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<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
</tr>
<tr>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has zero output impedance. That means, when it drives its output to 0V, it will maintain 0V regardless of how much current it has to sink in order to do so. Real comparators are pretty good -- if forced to sink too much current they may burn up, but the output voltage won't rise more than 100mV or so. </div></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has zero output impedance. That means, when it drives its output to 0V, it will maintain 0V regardless of how much current it has to sink in order to do so. Real comparators are pretty good -- if forced to sink too much current they may burn up, but the output voltage won't rise more than 100mV or so. </div></td>
</tr>
<tr>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
</tr>
<tr>
<td class="diff-marker" data-marker="−"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del style="font-weight: bold; text-decoration: none;">[[image:light.jpg|right]] </del>We will focus on the LM311P, a particularly nice comparator. Look up its datasheet. In the application shown, it is performing as a thresholding detector for a phototransistor. The trimmer potentiometer sets V- to an adjustable potential between 0V and 5V. If the phototransistor receives enough light and conducts enough current to bring V+ above the potential of V-, the output of the comparator goes high.</div></td>
<td class="diff-marker" data-marker="+"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>We will focus on the LM311P, a particularly nice comparator. Look up its datasheet. In the application shown, it is performing as a thresholding detector for a phototransistor. The trimmer potentiometer sets V- to an adjustable potential between 0V and 5V. If the phototransistor receives enough light and conducts enough current to bring V+ above the potential of V-, the output of the comparator goes high.</div></td>
</tr>
<tr>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><br></div></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><br></div></td>
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</table>LIMShttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=4863&oldid=prevLIMS at 13:13, 12 January 20072007-01-12T13:13:04Z<p></p>
<table style="background-color: #fff; color: #202122;" data-mw="interface">
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 08:13, 12 January 2007</td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has zero output impedance. That means, when it drives its output to 0V, it will maintain 0V regardless of how much current it has to sink in order to do so. Real comparators are pretty good -- if forced to sink too much current they may burn up, but the output voltage won't rise more than 100mV or so. </div></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has zero output impedance. That means, when it drives its output to 0V, it will maintain 0V regardless of how much current it has to sink in order to do so. Real comparators are pretty good -- if forced to sink too much current they may burn up, but the output voltage won't rise more than 100mV or so. </div></td>
</tr>
<tr>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
</tr>
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<td colspan="2" class="diff-empty diff-side-deleted"></td>
<td class="diff-marker"><a class="mw-diff-movedpara-right" title="Paragraph was moved. Click to jump to old location." href="#movedpara_3_1_lhs">⚫</a></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><a name="movedpara_1_0_rhs"></a><ins style="font-weight: bold; text-decoration: none;">[[image:light.jpg|right]] </ins>We will focus on the LM311P, a particularly nice comparator. Look up its datasheet. In the application shown, it is performing as a thresholding detector for a phototransistor. The trimmer potentiometer sets V- to an adjustable potential between 0V and 5V. If the phototransistor receives enough light and <ins style="font-weight: bold; text-decoration: none;">conducts</ins> enough current to bring V+ above the potential of V-, the output of the comparator goes high.</div></td>
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<td class="diff-marker" data-marker="−"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>[[image:light.jpg|right]] </div></td>
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</tr>
<tr>
<td class="diff-marker" data-marker="−"></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td class="diff-marker"><a class="mw-diff-movedpara-left" title="Paragraph was moved. Click to jump to new location." href="#movedpara_1_0_rhs">⚫</a></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><a name="movedpara_3_1_lhs"></a>We will focus on the LM311P, a particularly nice comparator. Look up its datasheet. In the application shown, it is performing as a thresholding detector for a phototransistor. The trimmer potentiometer sets V- to an adjustable potential between 0V and 5V. If the phototransistor receives enough light and <del style="font-weight: bold; text-decoration: none;">coducts</del> enough current to bring V+ above the potential of V-, the output of the comparator goes high.</div></td>
<td colspan="2" class="diff-empty diff-side-added"></td>
</tr>
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<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td class="diff-marker"></td>
<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><br></div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><br></div></td>
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</table>LIMShttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=4862&oldid=prevLIMS at 13:12, 12 January 20072007-01-12T13:12:39Z<p></p>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>A comparator subtracts two voltages and gives you a logic output. Thus it lives at the boundary between the analog world of continuous voltages, and the digital world of 1's and 0's, represented by +5V and 0V, logic high and logic low.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">[[image:just5.jpg|right]] </ins>A comparator subtracts two voltages and gives you a logic output. Thus it lives at the boundary between the analog world of continuous voltages, and the digital world of 1's and 0's, represented by +5V and 0V, logic high and logic low.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Comparators have two inputs, called inverting and non-inverting inputs, and labeled simply - and + on a circuit diagram. We will call the potential at these inputs V<sub>--</sub> and V<sub>+</sub>. Don't confuse these inputs with power supply connections! See figure 1: inputs on the side, power on the top and bottom. Often power is not even shown, but if you neglect to provide it the chip won't work. <del style="font-weight: bold; text-decoration: none;">[[image:just5.jpg|right]]</del></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Comparators have two inputs, called inverting and non-inverting inputs, and labeled simply - and + on a circuit diagram. We will call the potential at these inputs V<sub>--</sub> and V<sub>+</sub>. Don't confuse these inputs with power supply connections! See figure 1: inputs on the side, power on the top and bottom. Often power is not even shown, but if you neglect to provide it the chip won't work. </div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The output of a comparator is logic high (+5V) if V<sub>+</sub> > V<sub>--</sub> and low (0V) if V<sub>+</sub> < V<sub>--</sub> . If they are within 1mV of equal, anything goes.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The output of a comparator is logic high (+5V) if V<sub>+</sub> > V<sub>--</sub> and low (0V) if V<sub>+</sub> < V<sub>--</sub> . If they are within 1mV of equal, anything goes.</div></td>
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</table>LIMShttps://hades.mech.northwestern.edu//index.php?title=Comparators&diff=4861&oldid=prevLIMS at 13:12, 12 January 20072007-01-12T13:12:21Z<p></p>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has infinite input impedance. That means that it observes the voltage at its input while allowing no current to flow. Real comparators are pretty close to this ideal, swallowing only a few nA. This is very useful when you have a high impedance signal (having very little current available) such as a phototransistor.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has infinite input impedance. That means that it observes the voltage at its input while allowing no current to flow. Real comparators are pretty close to this ideal, swallowing only a few nA. This is very useful when you have a high impedance signal (having very little current available) such as a phototransistor.</div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has zero output impedance. That means, when it drives its output to 0V, it will maintain 0V regardless of how much current it has to sink in order to do so. Real comparators are pretty good -- if forced to sink too much current they may burn up, but the output voltage won't rise more than 100mV or so.</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>An ideal comparator, like an ideal opamp, has zero output impedance. That means, when it drives its output to 0V, it will maintain 0V regardless of how much current it has to sink in order to do so. Real comparators are pretty good -- if forced to sink too much current they may burn up, but the output voltage won't rise more than 100mV or so.<ins style="font-weight: bold; text-decoration: none;"> </ins></div></td>
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<td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br /></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>[[image:light.jpg|right]] </div></td>
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<td class="diff-marker"><a class="mw-diff-movedpara-left" title="Paragraph was moved. Click to jump to new location." href="#movedpara_5_1_rhs">⚫</a></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><a name="movedpara_4_0_lhs"></a>We will focus on the LM311P, a particularly nice comparator. Look up its datasheet. <del style="font-weight: bold; text-decoration: none;"> [[image:light.jpg|right]]</del> In the application shown, it is performing as a thresholding detector for a phototransistor. The trimmer potentiometer sets V- to an adjustable potential between 0V and 5V. </div></td>
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<td class="diff-marker"><a class="mw-diff-movedpara-right" title="Paragraph was moved. Click to jump to old location." href="#movedpara_4_0_lhs">⚫</a></td>
<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><a name="movedpara_5_1_rhs"></a>We will focus on the LM311P, a particularly nice comparator. Look up its datasheet. In the application shown, it is performing as a thresholding detector for a phototransistor. The trimmer potentiometer sets V- to an adjustable potential between 0V and 5V. <ins style="font-weight: bold; text-decoration: none;">If the phototransistor receives enough light and coducts enough current to bring V+ above the potential of V-, the output of the comparator goes high.</ins></div></td>
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</table>LIMS