PLL circuit, and radio communication apparatus equipped with same

1. A PLL circuit comprising:

a digitally controlled oscillator for oscillating at a frequency according to a set digital value;

a phase detector for generating a phase error value by detecting an error between an output phase of the digitally controlled oscillator and a reference phase based on a set frequency control digital value;

a loop filter for generating a first digital tuning value by multiplying a phase error value output from the phase detector by a predetermined loop gain;

an oscillator gain normalization unit which generates a second digital tuning value set in the digitally controlled oscillator, by multiplying the first digital tuning value output from the loop filter by a predetermined reference frequency and dividing the value by a set gain of the digitally controlled oscillator;

an oscillator gain estimation unit which estimates the gain of the digitally controlled oscillator, on the basis of the second digital tuning value output from the oscillator gain normalization unit; and

a mode switch unit which switches the value of the loop gain set in the loop filter in a stepwise manner during tuning, wherein

in a certain mode, the oscillator gain estimation unit estimates the gain of the digitally controlled oscillator from a ratio between a change of a frequency of the output signal of the digitally controlled oscillator and a change of the second digital tuning value obtained by changing the frequency control digital value, and

the oscillator gain estimation unit estimates a gain of the digitally controlled oscillator in another mode, on the basis of a device parameter of the digitally controlled oscillator and the gain of the digitally controlled oscillator estimated in the certain mode.

2. The PLL circuit according to claim 1 , wherein

the digitally controlled oscillator includes an LC oscillator,

the LC oscillator includes a plurality of capacitor arrays corresponding to the number of modes,

each capacitor array includes a plurality of varactors,

a combined capacitance of the plurality of varactors is set by the second digital tuning value, and

the oscillator gain estimation unit estimates the gain of the digitally controlled oscillator in another mode on the basis of the gain of the digitally controlled oscillator estimated in the certain mode and a ratio between a unit step width of a combined capacitance of the capacitor array for the certain mode and a unit step width of the combined capacitance of the capacitor array for the another mode.

3. The PLL circuit according to claim 2 , wherein

during tuning, the mode switch unit switches a mode from a rough adjustment mode in which the frequency of the output signal of the digitally controlled oscillator is roughly changed to a fine adjustment mode in which the frequency is changed finely as compared with the rough adjustment mode, and

the oscillator gain estimation unit estimates a gain of the digitally controlled oscillator in the fine adjustment mode on the basis of the gain of the digitally controlled oscillator estimated in the rough adjustment mode and a ratio between a unit step width of a combined capacitance of the capacitor array for the rough adjustment mode and a unit step width of a combined capacitance of the capacitor array for the fine adjustment mode.

4. The PLL circuit according to claim 2 , wherein during

tuning, the mode switch unit switches, in order, to a large mode in which the frequency of the output signal of the digitally controlled oscillator is changed most greatly, to a middle mode in which the frequency is changed less greatly than the large mode, and to a small mode in which the frequency is changed less greatly than the middle mode, and

the oscillator gain estimation unit estimates a gain of the digitally controlled oscillator in the small mode on the basis of the gain of the digitally controlled oscillator estimated in the middle mode and a ratio between a unit step width of a combined capacitance of the capacitor array for the middle mode and a unit step width of a combined capacitance of the capacitor array for the small mode.

5. A PLL circuit comprising:

a digitally controlled oscillator for oscillating at a frequency according to a set digital value;

a phase detector for generating a phase error value by detecting an error between an output phase of the digitally controlled oscillator and a reference phase based on a set frequency control digital value;

a loop filter for generating a first digital tuning value by multiplying a phase error value output from the phase detector by a predetermined loop gain;

an oscillator gain normalization unit which generates a second digital tuning value set in the digitally controlled oscillator, by multiplying the first digital tuning value output from the loop filter by a predetermined reference frequency and dividing the value by a set gain of the digitally controlled oscillator;

an oscillator gain estimation unit which estimates the gain of the digitally controlled oscillator, on the basis of the second digital tuning value output from the oscillator gain normalization unit; and

a mode switch unit which switches the value of the loop gain set in the loop filter in a stepwise manner during tuning, wherein

the oscillator gain estimation unit estimates the gain of the digitally controlled oscillator from time-change data of each of the first digital tuning value, the second digital tuning value, and the frequency of the output signal of the PLL circuit, and

the oscillator gain estimation unit estimates a gain of the digitally controlled oscillator in another mode, on the basis of a device parameter of the digitally controlled oscillator and the gain of the digitally controlled oscillator estimated in the certain mode.

6. A radio communication apparatus comprising:

an antenna for receiving a radio signal;

a local oscillator using the PLL circuit according to claim 1 ; and

a demodulation unit which demodulates a radio signal received with the antenna on the basis of a signal provided from the local oscillator.