| 摘要 |
PROBLEM TO BE SOLVED: To reduce modulation deviation by connecting a cathode of a varactor diode of a variable capacitance circuit to a control voltage terminal and connecting the cathode to a modulation signal input terminal via a coupling resistor with a high resistance. SOLUTION: A modulation signal input terminal 8 is connected to a cathode of a varactor diode 9 via a resistor 14 and a coupling resistor 22. A modulation signal received from the modulation signal input terminal 8 is divided by resistors 14, 15 and given to the cathode of the varactor diode 9 via the coupling resistor 22. Since the resistance of the coupling resistor 22 is selected to be a resistance (e.g. 3Mohms) sufficiently higher than the resistance of the voltage division resistors, almost no current flows to the coupling resistor 22, and only a voltage change in a connection of the resistors 14, 15 due to a modulation signal is given to the cathode of the varactor diode 9. Then a relative change in an oscillated frequency with respect to a constant modulation signal does not vary much even when the oscillated frequency is high or low to reduce the modulation deviation. |
