| 摘要 |
PURPOSE:To set the frequency to a center frequency automatically by applying switching operation to return an external signal or a received input to an output of a D/A converter circuit DAC when the external signal or the received input level is less than a prescribed level. CONSTITUTION:An oscillator circuit is adopted for a voltage controlled oscillator VCO 11, AFC is implemented by PLL control and an SG or a stable frequency from a base station or the like is used as a reference frequency to make the frequency stable. Then the control voltage of the VCO 11 is converted into a digital value by an A/D converter circuit ADC 18, the digital value is stored in an EEPROM or a RAM 19 and when the input from a base station or the like is zero, the stored digital value is converted by a D/A converter circuit DAC 20 to set the center frequency fed to the VCO 11 and to correct a secular change. Thus, the center frequency is set externally. |
