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宽范围、高线性的脉冲频率调制器是PFM-IM制式彩色电视光纤传输系统的核心。用PFM-IM方式进行彩色电视信号的光纤传输,失真小,传输信噪比高,传输距离远,系统造价适中,所以受到国内外重视。其中的脉冲频率调制器对系统的指标起着重要作用。本文先简述其工作原理,进而讨论设计原则,最后导出工程设计方法,并给出设计实例。一、PFM调制器的工作原理 PFM-IM彩色电视光纤传输系统中的脉冲频率调制器实际上是一个高工作频率、高线性度,宽频率复盖范围的压控振荡器,控制电压就是所要传输的彩色电视信号(需要时还可混入伴音调频信号和数字调制信号,共同组成基带信号)。定量充放电型压控振荡器可以很好地满足各项要求。它的调制特性如图1所示,工作原理可由图2说明。图2中is为电容C的充电恒流源,它随控制电压
The wide range, high linearity pulse frequency modulator is the core of the PFM-IM standard color television optical fiber transmission system. PFM-IM way for the color television signal transmission, low distortion, high transmission SNR, transmission distance, the system cost is moderate, so by domestic and international attention. The pulse frequency modulator of the system plays an important role in the index. This article first briefly describes its working principle, and then discusses the design principles, and finally derives engineering design methods, and gives the design examples. First, the working principle of PFM modulator PFM-IM color TV optical fiber transmission system is actually a pulse frequency modulator high frequency, high linearity, wide frequency coverage of the voltage-controlled oscillator, the control voltage is the desired transmission Of the color television signal (if necessary, can also be mixed with audio frequency modulation signal and digital modulation signal, together form the baseband signal). Quantitative charge and discharge voltage-controlled oscillator can well meet the requirements. Its modulation characteristics shown in Figure 1, the working principle can be illustrated in Figure 2. Figure 2 is the capacitor C charging constant current source, it with the control voltage