| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the necessity of mechanical adjustment of the frequency modulated width in an FSK (frequency shift keying) modulation circuit in which a switching element switches a predetermined power supply voltage in accordance with a transmission signal and gives the power supply voltage to a variable capacitance capacitor disposed in an oscillation circuit, thereby executing frequency modulation on the basis of a change in capacitance of the variable capacitance capacitor using the transmission signal. SOLUTION: The FSK modulation circuit 21 has a configuration in which a transmission signal from an output port TX of a CPU 22 is amplified by an amplification transistor 3, and the amplified transmission signal is given via an LPF 4 for waveform shaping to an oscillation circuit 5 provided with a variable capacitance capacitor 7 for executing frequency modulation based on the change in capacitance in an LC parallel resonant circuit 6, thereby executing FSK modulation. In this FSK modulation circuit 21, the power supply voltage of the transistor 3 is generated by DC-smoothing a PWM signal from a PWM port of the CPU 22 by an LPF 23. As described above, since the power supply voltage itself is adjusted, a resistor 24 can be used as a fixed resistor and the necessity of mechanical adjustment can be eliminated. COPYRIGHT: (C)2009,JPO&INPIT
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