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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Differential amplifier ： ウィキペディア英語版 Differential amplifier A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs $\backslash scriptstyle\; V\_\backslash text^-$ and $\backslash scriptstyle\; V\_\backslash text^+$ and one output $\backslash scriptstyle\; V\_\backslash text$ in which the output is ideally proportional to the difference between the two voltages :$V\_\backslash text\; =\; A(V\_\backslash text^+\; -\; V\_\backslash text^-)$ where $\backslash scriptstyle\; A$ is the gain of the amplifier. == Theory == Many electronic devices use differential amplifiers internally. The output of an ideal differential amplifier is given by: :$V\_\backslash text\; =\; A\_\backslash text(V\_\backslash text^+\; -\; V\_\backslash text^-)$ Where $V\_\backslash text^+$ and $V\_\backslash text^-$ are the input voltages and $A\_\backslash text$ is the differential gain. In practice, however, the gain is not quite equal for the two inputs. This means, for instance, that if $V\_\backslash text^+$ and $V\_\backslash text^-$ are equal, the output will not be zero, as it would be in the ideal case. A more realistic expression for the output of a differential amplifier thus includes a second term. :$V\_\backslash text\; =\; A\_\backslash text(V\_\backslash text^+\; -\; V\_\backslash text^-)\; +\; A\_\backslash text\backslash left(\backslash frac^-\}\backslash right)$ $A\_\backslash text$ is called the common-mode gain of the amplifier. As differential amplifiers are often used to null out noise or bias-voltages that appear at both inputs, a low common-mode gain is usually desired. The common-mode rejection ratio (CMRR), usually defined as the ratio between differential-mode gain and common-mode gain, indicates the ability of the amplifier to accurately cancel voltages that are common to both inputs. The common-mode rejection ratio is defined as: :$\backslash mathrm\; =\; 10\backslash log\_\; \backslash left\; (\backslash frac\}\; \backslash right)^2\; =\; 20\backslash log\_\; \backslash left\; (\backslash frac|\}\; \backslash right)$ In a perfectly symmetrical differential amplifier, $A\_\backslash text$ is zero and the CMRR is infinite. Note that a differential amplifier is a more general form of amplifier than one with a single input; by grounding one input of a differential amplifier, a single-ended amplifier results. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Differential amplifier」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.