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A fully differential amplifier, usually referred to as an 'FDA' for brevity, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and differential outputs. In its ordinary usage, the output of the FDA is controlled by two feedback paths which, because of the amplifier's high gain, almost completely determine the output voltage for any given input. In a fully differential amplifier, common-mode noise such as power supply disturbances is rejected; this makes FDAs especially useful as part of a mixed-signal integrated circuit.〔Nancy Y. Sun. ("A DC Stabilized Fully Differential Amplifier" ). 2005. p. 22. 〕 An FDA is often used to convert an analog signal into a form more suitable for driving into an analog-to-digital converter; many modern high-precision ADCs have differential inputs.〔 Jim Karki. ("Fully differential amplifiers" ). 2000. 〕〔 Michael Steffes. ("Wideband fully differential amplifier noise improved using active match" ). 2013-06-09. 〕〔 Rick. ("ADC Input Driver FULLY DIFFERENTIAL AMPLIFIER" ) 〕 == The Ideal FDA == For any input voltages the ''ideal'' FDA has infinite open-loop gain, infinite bandwidth, infinite input impedances resulting in zero input currents, infinite slew rate, zero output impedance and zero noise. In the ideal FDA, the difference of the output voltages is equal the difference between the input voltages multiplied by the gain. The common mode voltage of the output voltages is not dependent of the input voltage. In many cases, the common mode voltage can be directly set by a third voltage input. * Input voltage: * Output voltage: 〔 * Output common-mode voltage: 〔 A real FDA can only approximate this ideal, and the actual parameters are subject to drift over time and with changes in temperature, input conditions, etc. Modern integrated FET or MOSFET FDAs approximate more closely to these ideals than bipolar ICs where large signals must be handled at room temperature over a limited bandwidth; input impedance, in particular, is much higher, although the bipolar FDA usually exhibit superior (i.e., lower) input offset drift and noise characteristics. Where the limitations of real devices can be ignored, an FDA can be viewed as a Black Box with gain; circuit function and parameters are determined by feedback, usually negative. An FDA as implemented in practice is moderately complex integrated circuit. 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「Fully differential amplifier」の詳細全文を読む スポンサード リンク
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