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Pulse-Frequency Modulation (PFM) is a modulation method for representing an analog signal using only two levels (1 and 0). It is analogous to Pulse-Width Modulation (PWM), in which the magnitude of an analog signal is encoded in the duty cycle of a square wave. Unlike PWM, in which the width of square pulses is varied at constant frequency, PFM is accomplished using fixed-duration pulses and varying the repetition rate thereof. In other words, the frequency of the pulse train is varied in accordance with the instantaneous amplitude of the modulating signal at sampling intervals. The amplitude and width of the pulses is kept constant. The advantage of pulse frequency modulation is better immunity to noise interference than Pulse-Amplitude Modulation (PAM). The disadvantage is more complex transmitter and receiver design. The spike-rate coding model of neuronal communication is the same as pulse frequency modulation.〔 Albert Y. Zomaya. ("Handbook of Nature-Inspired and Innovative Computing: Integrating Classical Models with Emerging Technologies" ). 2006. Section 5.4: Implementing spiking neurons. p. 459. 〕 ==Potential applications== It has been proposed that PFM could serve as a suitable retinal prosthesis device. PFM's ability to operate independently and asynchronously promotes the flow of nutrients through the chip which is essential for living cells. Cell stimulation would be accomplished through the output of pulse streams by PFM. A large dynamic range is also practical in the replacement of photoreceptors.〔Ohta, J., Yoshida, N., Kagawa, K., & Nunoshita, N. (2002). Proposal of Application of Pulsed Vision Chip for Retinal Prosthesis. Japanese Journal of Applied Physics , 2322-2325.〕 PFM could be used to transmit intelligence signals, such as audio signals, by demodulating the signal from the receiving end at the transmitting end. 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「Pulse-frequency modulation」の詳細全文を読む スポンサード リンク
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