| 摘要 |
A two-point frequency modulation apparatus is proposed whereby the spectrum of transmission waves is kept within the spectrum mask. Voltage is supplied to the control voltage terminal of VCO 1 in accordance with modulation data via noise shaper 101 that has operating characteristics of attenuating more noise at higher frequencies. As a result, by virtue of the working of noise shaper 101, the signal level outputted from the PLL circuit combining the modulation signal and the quantization noise decreases in proportion to the distance form the central frequency, so that two-point frequency modulation apparatus 100 is made possible whereby the spectrum of an RF modulation signal is kept within the spectrum mask.
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