The pfm technology includes two kinds modes : constant width pfm and swfm 脉冲频率调制又包括了两种方式，即等宽pfm和swfm 。
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The swfm mode is adopted as the modulation of the optic transmitter in the circuit ' s design by researching the advantages and disadvantages when the two ways are used to transmit the signals . the mc1658 which is adopted by the most designers is used to accomplish the swfm modulation here 对比研究了利用这两种方式进行信号传输的优缺点，并在电路设计中选择swfm方式作为光发射机的调制方式，采用目前大多数设计者使用的mc1658来完成swfm调制，而等宽pfm方式作为接收机的解调方式。
