| 摘要 |
PROBLEM TO BE SOLVED: To provide the tuning control system suitable for circuit integration in which fluctuation in a tuning frequency is prevented even in the case of circuit integration. SOLUTION: A tuning mechanism adopting the tuning control system has a phase locked loop including a tuning amplifier 1 whose tuning frequency is revised depending on a control voltage, a charge pump and a low pass filter. The tuning amplifier 1 is made up of a noninverting circuit 50, two phase shift circuits 10C, 30C and a voltage division circuit 60 connected in cascade, and an adder circuit consisting of a feedback resistor 70 and an input resistor 74. Each of the phase shift circuits 10c, 30c is made up of a 1st series circuit consisting of two resistors nearly halving an amplitude of a received AC signal, a 2nd series circuit consisting of a capacitor and a variable resistor to shift a phase of the received AC signal by a prescribed phase, and a differential amplifier amplifying a difference between the outputs of the 1st and 2nd series circuits and the tuning frequency of the tuning amplifier 1 is controlled constant by changing a resistance of the resistor being a component of the 2nd series circuit in response to an output voltage of the low pass filter. |
