| 摘要 |
A phase-locked loop circuit includes a voltage-controlled oscillator that includes a series circuit having a P-channel transistor, N-channel transistor, a third resistor and a first resistor connected in series in this order; a second resistor connected in parallel with a series circuit of the N-channel transistor and the third resistor; and an operational amplifier having its non-inverting input terminal connected to an output terminal of a lowpass filter, its inverting input terminal connected to a connected point of the third resistor and first resistor, and its output terminal connected to a gate of the N-channel transistor. The variable region of the resistance of the parallel circuit consisting of the N-channel transistor and the third and first resistors can be limited, which in turn enables the variable region of the control voltage of the voltage-controlled oscillator including a locking control voltage to be limited to a desired range. This makes it possible to limit the oscillation frequency of the voltage-controlled oscillator determined by the voltage signal fed from the lowpass filter to a desired range, and to increase its lock speed and stability at the same time.
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