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An operational amplifier (a.k.a. "op-amp") is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.〔(Maxim Application Note 1108: Understanding Single-Ended, Pseudo-Differential and Differential ADC Inputs ) – Retrieved November 10, 2007〕 In this configuration, an op-amp produces an output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the potential difference between its input terminals.〔(Analog devices MT-044 Tutorial )〕 Operational amplifiers had their origins in analog computers, where they were used to do mathematical operations in many linear, non-linear and frequency-dependent circuits. The popularity of the op-amp as a building block in analog circuits is due to its versatility. Due to negative feedback, the characteristics of an op-amp circuit, its gain, input and output impedance, bandwidth etc. are determined by external components and have little dependence on temperature coefficients or manufacturing variations in the op-amp itself. Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities.〔(【引用サイトリンク】url=http://www.digikey.com/product-detail/en/PA98/598-1337-ND/1761961 )〕 Op-amps may be packaged as components, or used as elements of more complex integrated circuits. The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network). ==Operation== The amplifier's differential inputs consist of a non-inverting input (+) with voltage ''V''+ and an inverting input (–) with voltage ''V''−; ideally the op-amp amplifies only the difference in voltage between the two, which is called the ''differential input voltage''. The output voltage of the op-amp ''V''out is given by the equation: : where ''A''OL is the open-loop gain of the amplifier (the term "open-loop" refers to the absence of a feedback loop from the output to the input). 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「Operational amplifier」の詳細全文を読む スポンサード リンク
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