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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 Phase modulation ： ウィキペディア英語版 Phase modulation Phase modulation (PM) is a modulation pattern that encodes information as variations in the instantaneous phase of a carrier wave. Phase modulation is widely used for transmitting radio waves and is an integral part of many digital transmission coding schemes that underlie a wide range of technologies like WiFi, GSM and satellite television. PM is used for signal and waveform generation in digital synthesizers, such as the Yamaha DX7 to implement FM synthesis. A related type of sound synthesis called phase distortion is used in the Casio CZ synthesizers. ==Theory== PM changes the phase angle of the complex envelope in direct proportion to the message signal. Suppose that the signal to be sent (called the modulating or message signal) is $m(t)$ and the carrier onto which the signal is to be modulated is :$c(t)\; =\; A\_c\backslash sin\backslash left(\backslash omega\_\backslash mathrmt\; +\; \backslash phi\_\backslash mathrm\backslash right).$ Annotated: :carrier(time) = (carrier amplitude) *sin(carrier frequency *time + phase shift) This makes the modulated signal :$y(t)\; =\; A\_c\backslash sin\backslash left(\backslash omega\_\backslash mathrmt\; +\; m(t)\; +\; \backslash phi\_\backslash mathrm\backslash right).$ This shows how $m(t)$ modulates the phase - the greater m(t) is at a point in time, the greater the phase shift of the modulated signal at that point. It can also be viewed as a change of the frequency of the carrier signal, and phase modulation can thus be considered a special case of FM in which the carrier frequency modulation is given by the time derivative of the phase modulation. The modulation signal could here be :$m(t)\; =\; \backslash cos\backslash left(\backslash omega\_\backslash mathrm\; t\; +\; k\backslash omega\_\backslash mathrm(t)\backslash right)\backslash$ The mathematics of the spectral behavior reveals that there are two regions of particular interest: *For small amplitude signals, PM is similar to amplitude modulation (AM) and exhibits its unfortunate doubling of baseband bandwidth and poor efficiency. *For a single large sinusoidal signal, PM is similar to FM, and its bandwidth is approximately ::$2\backslash left(h\; +\; 1\backslash right)f\_\backslash mathrm$, :where $f\_\backslash mathrm\; =\; \backslash omega\_\backslash mathrm/2\backslash pi$ and $h$ is the modulation index defined below. This is also known as Carson's Rule for PM. 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「Phase modulation」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.