| 摘要 |
PROBLEM TO BE SOLVED: To provide a UHF (ultrahigh frequency) band frequency FM transmitter for a wireless microphone which is difficult to invite audible noise occurrence that is caused by vibrations, feedback, etc., and is made small and inexpensive. SOLUTION: This UHF band carrier FM transmitter for a wireless microphone which adopts a PLL system has a voltage control crystal oscillator (VCXO) 50 which performs FM modulation of an oscillation frequency of a crystal oscillator circuit through a modulation signal input AF of an acoustic signal and uses an FM modulation signal fr that is acquired from the VCXO 50 as a reference signal Vr to be inputted to an analog phase comparator (PC) 61 of a PLL circuit 60. Since the PC 61 performs a phase comparison operation at a high speed (10 MHz or more), a cutoff frequency of a loop filter 62 can be a high pass frequency of about 100 kHz to 1 MHz and a frequency that is by far higher than the highest audible frequency can be selected. Because filter output is shifted in an inaudible frequency, the occurrence of audible noise is not invited, and shield measures and vibration proof measures are made unnecessary, miniaturization and cost reduction can be realized. |
