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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 Negative impedance converter ： ウィキペディア英語版 Negative impedance converter The negative impedance converter (NIC) is a one-port op-amp circuit acting as a negative load which injects energy into circuits in contrast to an ordinary load that consumes energy from them. This is achieved by adding or subtracting excessive varying voltage in series to the voltage drop across an equivalent positive impedance. This reverses the voltage polarity or the current direction of the port and introduces a phase shift of 180° (inversion) between the voltage and the current for any signal generator. The two versions obtained are accordingly a ''negative impedance converter with voltage inversion'' (VNIC) and a ''negative impedance converter with current inversion'' (INIC). The basic circuit of an INIC and its analysis is shown below. ==Basic circuit and analysis== INIC is a non-inverting amplifier (the op-amp and the voltage divider R1, R2 on the figure) with a resistor (R3) connected between its output and input. The op-amp output voltage is :$V\_\; \backslash right)\backslash ,$ The current going from the operational amplifier output through resistor $R\_3$ ''toward'' the source $V\_s$ is $-I\_s$, and :$-I\_s\; =\; \backslash frac\; =\; V\_s\; \backslash frac\; \}.$ So the input $V\_s$ experiences an ''opposing'' current $-I\_s$ that is proportional to $V\_s$, and the circuit acts like a resistor with ''negative'' resistance :$R\_\; =\; -R\_3\; \backslash frac.$ In general, elements $R\_1$, $R\_2$, and $R\_3$ need not be pure resistances (i.e., they may be capacitors, inductors, or impedance networks). ==Application== (詳細はcurrent generator and the resistor within the dotted line is the Norton representation of a circuit comprising a real generator and $R\_s$ is its internal resistance. If an INIC is placed in parallel to that internal resistance, and the INIC has the same magnitude but inverted resistance value, there will be $R\_s$ and $-R\_s$ in parallel. Hence, the equivalent resistance is :$\backslash lim\backslash limits\_\; R\_s\; \backslash |\; (-R\_\}\; \backslash to\; R\_s+\}\; \backslash frac\; =\; \backslash infty.$ That is, the combination of the real generator and the INIC will now behave like a composed ideal current source; its output current will be the same for any load $Z\_L$. In particular, any current that is shunted away from the load into the Norton equivalent resistance $R\_s$ will be supplied by the INIC instead. The ideal behavior in this application depends upon the Norton resistance $R\_s$ and the INIC resistance $R\_\}\; >\; R\_s$, the equivalent resistance of the combination will be greater than $R\_s$; however, if $R\_\; >\; \backslash frac\; +\; \backslash frac,\; \backslash quad\; \backslash text\; \backslash ,\; R\_\backslash ,$ the circuit is unstable (e.g., when in an unloaded system). In particular, the surplus current from the INIC generates positive feedback that causes the voltage driving the load to reach its power supply limits. By reducing the impedance of the load (i.e., by causing the load to draw more current), the generator–NIC system can be rendered stable again. In principle, if the Norton equivalent current source was replaced with a Norton equivalent voltage source, a VNIC of equivalent magnitude could be placed in ''series'' with the voltage source's series resistance. Any voltage drop across the series resistance would then be added back to the circuit by the VNIC. However, a VNIC implemented as above with an operational amplifier must terminate on an electrical ground, and so this use is not practical. Because any voltage source with nonzero series resistance can be represented as an equivalent current source with finite parallel resistance, an INIC will typically be placed in parallel with a source when used to improve the impedance of the source. 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「Negative impedance converter」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.