Patent ID: 7965144

Claim:
A phase locked loop circuit comprising: a voltage controlled oscillator; a variable frequency-dividing circuit for frequency-dividing an oscillation signal having an oscillation frequency of the voltage controlled oscillator into a frequency-dividing signal having a frequency of (1/N) (N: positive integral number) of the oscillation frequency of the oscillation signal; a phase comparing circuit for comparing a phase of the frequency-dividing signal outputted from the variable frequency-dividing circuit, and a phase of a signal having a reference frequency with each other; a charge pump circuit to which a comparison output signal is supplied from the phase comparing circuit; a loop filter for fetching a direct current component from an output signal from the charge pump circuit, and supplying the direct current component thus fetched as a control signal for the oscillation frequency of the voltage controlled oscillator to the voltage controlled oscillator; a voltage supplying circuit for, in a phase of measurement, supplying a predetermined first control voltage as a control signal for the oscillation frequency of the voltage controlled oscillator to the voltage controlled oscillator instead of the output signal from the charge pump circuit; a frequency measuring circuit for, in the phase of the measurement, measuring the oscillation frequency of the voltage controlled oscillator; and a voltage measuring circuit for, in a phase of use, measuring a magnitude of a second control voltage supplied as a control signal for the oscillation frequency of the voltage controlled oscillator to the voltage controlled oscillator; wherein in the phase of the measurement, a data table representing a relationship between the first control voltage, and a rate of a change in oscillation frequency of the voltage controlled oscillator is created by the voltage supplying circuit and the frequency measuring circuit; in the phase of the use, the second control voltage measured by the voltage measuring circuit is converted into a control sensitivity representing the rate of the change in oscillation frequency by referring to the data table; and a magnitude of a charge pump current of the charge pump circuit is controlled by using the control sensitivity as a result of the conversion so that a transfer function in a phase of an open loop becomes constant irrespective of the frequency-dividing ratio N, wherein the voltage supplying circuit including: a digital to analog converter circuit; and a control circuit for supplying digital data which is digital to analog-converted into the first control voltage to the digital to analog converter; and the voltage measuring circuit including an analog to digital converter circuit for analog to digital-converting the second control voltage, and supplying the resulting digital voltage to the control circuit.