en>Tom.Reding: WP:GenFixes (page/s, endash, , unicodify, and/or concising wikilinks, etc.), et al., ed., ref cleanup using AWB

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WP:GenFixes (page/s, endash, &nbsp, unicodify, and/or concising wikilinks, etc.), et al., ed., ref cleanup using AWB

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← Older revision		Revision as of 10:02, 7 March 2013
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	~~Hello~~, ~~dear friend! I am Zak~~. ~~I am delighted that I could unify to~~ the ~~entire world~~. ~~I live~~ in ~~United Kingdom~~, in the ~~region~~. ~~I dream~~ to ~~see~~ the ~~different countries~~, to ~~obtain acquainted with appealing individuals~~.<br><br>~~Look into my web blog~~: ~~Fifa 15 Coin Generator~~ ([http://~~Xp5~~.~~net~~/~~profile~~/~~tacollie Xp5~~.~~Net~~])		The '''common-mode rejection ratio''' (CMRR) of a [[differential amplifier]] (or other device) is the rejection by the device of unwanted input signals common to both input leads, relative to the wanted difference signal. An ideal differential amplifier would have infinite CMRR; this is not achievable in practice. A high CMRR is required when a differential signal must be amplified in the presence of a possibly large common-mode input. An example is audio transmission over [[balanced line]]s.

			== Theory ==

			Ideally, a differential amplifier takes the voltages, <math>V_+</math> and <math>V_-</math> on its two inputs and produces an output voltage <math>V_\mathrm{o}=A_\mathrm{d}(V_+ - V_-)</math>, where <math>A_\mathrm{d}</math> is the differential gain. However, the output of a real differential amplifier is better described as
			:<math>V_{\mathrm{o}} = A_\mathrm{d} (V_+ - V_-) + \tfrac{1}{2} A_\mathrm{cm} (V_+ + V_-),</math>
			where <math>A_\mathrm{cm}</math> is the common-mode gain, which is typically much smaller than the [[differential gain]].

			The CMRR is defined as the ratio of the [[Power (physics)\|powers]] of the differential gain over the common-mode gain, measured in positive [[decibel]]s (thus using the [[20 log rule]]):
			:<math>\mathrm{CMRR} = \left (\frac{A_\mathrm{d}}{\|A_\mathrm{cm}\|} \right) = 10\log_{10} \left (\frac{A_\mathrm{d}}{A_\mathrm{cm}} \right)^2 dB = 20\log_{10} \left (\frac{A_\mathrm{d}}{\|A_\mathrm{cm}\|} \right) dB</math>

			As differential gain should exceed common-mode gain, this will be a positive number, and the higher the better.

			The CMRR is a very important specification, as it indicates how much of the [[common-mode signal]] will appear in your measurement. The value of the CMRR often depends on signal [[frequency]] as well, and must be specified as a [[function (mathematics)\|function]] thereof.

			It is often important in reducing noise on transmission lines. For example, when measuring the resistance of a [[thermocouple]] in a noisy environment, the [[signal noise\|noise]] from the environment appears as an offset on both input leads, making it a common-mode [[voltage]] signal. The CMRR of the measurement instrument determines the [[attenuation]] applied to the offset or noise.

			== Example: operational amplifiers ==

			[[File:Op-Amp Instrumentation Amplifier.svg\|right\|thumb\|Typical [[instrumentation amplifier]] implementation, designed to have a high CMRR.]]

			An [[operational amplifier]] (op-amp) has two inputs, V<sub>+</sub> and V<sub>-</sub>, and an [[open-loop gain]] G. In the ideal case, the output of an ideal op-amp behaves according to the equation

			:<math>V_\mathrm{out} = (V_+ - V_-) \cdot G_\mathrm{openloop}</math>

			This equation represents an infinite CMRR: if both inputs fluctuate by the same amount (while maintaining a constant difference V<sub>+</sub> - V<sub>-</sub>), this change will have no bearing on the output. In real applications, this is not always the case: the lower the CMRR, the larger the effect on the output signal, following the general equation

			:<math>V_\mathrm{out} = (V_+ - V_-) \cdot G_\mathrm{openloop} \pm \frac {V_\mathrm{cm}}{ 10 ^ {\frac {CMRR}{20}}} </math>

			Where V<sub>CM</sub> represents the common-mode voltage at the inputs, or (V<sub>+</sub> + V<sub>-</sub>)/2.

			The [[Operational amplifier#1968: Release of the .CE.BCA741\|741]] (a common op-amp chip) has a CMRR of 90 dB, which is reasonable in most cases. A value of 70 dB may be adequate for applications which are insensitive to the effects on amplifier output;some high-end devices may use op-amps with a CMRR of 120 dB or more.

			So for example, an op-amp with 90dB CMRR operating with 10V
			of common-mode will have an output error of ±316uV.

			== See also ==
			* [[Signal-to-noise ratio]]
			* [[Balanced line]]
			* [[XLR connector]]
			* [[Tip ring sleeve]]

			==External links==
			* [http://pages.emerson.edu/faculty/O/Owen%5FCurtin/Audio_Connectors.htm PowerPoint presentation on audio connectors]

			[[Category:Electronics]]
			[[Category:Engineering ratios]]

en>Mejor Los Indios at 22:01, 13 March 2011

2011-03-13T22:01:50Z

New page

Hello, dear friend! I am Zak. I am delighted that I could unify to the entire world. I live in United Kingdom, in the region. I dream to see the different countries, to obtain acquainted with appealing individuals.<br><br>Look into my web blog: Fifa 15 Coin Generator ([http://Xp5.net/profile/tacollie Xp5.Net])

Magnetosonic wave - Revision history

en>Tom.Reding: WP:GenFixes (page/s, endash, , unicodify, and/or concising wikilinks, etc.), et al., ed., ref cleanup using AWB

en>Addbot: Bot: Migrating 3 interwiki links, now provided by Wikidata on d:q844057

en>Mejor Los Indios at 22:01, 13 March 2011