PLL circuit and radio communication terminal apparatus using the same
View Patent ↗In a PLL circuit, the number of LPFs is reduced to one to reduce mounting area and pin number, and to simplify design. In one embodiment, the PLL circuit includes a variable-gain phase comparator, a mixer, an LPF, VCOs, couplers, and a control circuit to controlling the on/off operation of the VCOs. The variable-gain phase comparator is capable of varying a phase difference gain. The on/off of the operation of the VCOs is controlled by the control circuit so that one of the VCOs is turned off. The phase difference conversion gain is varied in accordance with the sensitivity of the VCOs so the number of LPFs required for the PLL circuit can be reduced to only one.
1. A radio communication circuitry, to be used in a radio communication terminal apparatus, comprising:
transmitting circuitry including a transmitting modulator to which transmitting I and Q base band signals and a transmitting intermediate frequency local signal are supplied and a phase locked loop circuit to which a modulated output signal from an output node of said transmitting modulator and a transmitting radio frequency local signal are supplied;
receiving circuitry receiving a radio frequency input signal received by an antenna of said radio communication terminal apparatus and outputting received I and Q base band signals,
wherein said transmitting modulator of said transmitting circuitry outputs a transmitting intermediate frequency transmitting output signal,
wherein an output terminal of said phase locked loop circuit is adapted to be coupled to an input terminal of a radio frequency power amplifier, an output terminal of which is adapted to be coupled to said antenna of said radio communication terminal apparatus,
wherein said phase locked loop circuit of said transmitting circuitry comprises:
a phase comparator to output a signal related to a phase difference between said transmitting intermediate frequency transmitting output signal and a feedback intermediate frequency signal, a frequency of which is converted from a frequency of said transmitting radio frequency transmitting output signal by a frequency conversion circuit;
a low-pass filter, an input of which is coupled to an output terminal of said phase comparator; and
a frequency generator, including a controlled oscillator, an input terminal of which is coupled to an output terminal of said low-pass filter and an output terminal of which is adapted to generate a plurality of oscillating signals of a plurality of frequency bands;
wherein selected ones of said plurality of frequencies oscillating signals generated by said frequency generator originates said frequency of said transmitting radio frequency transmitting output signal, and
wherein said phase comparator of said phase locked loop circuit of said transmitting circuitry is so controlled that a parameter of a product of a sensitivity between a frequency of an oscillating output signal and a control input signal of said frequency generator and a gain between an output signal and an input phase difference of said phase comparator is almost constant even when said selected one of said plurality of frequencies oscillating signals generated by said frequency generator is assigned to any one of said plurality of oscillating signals of said plurality of frequency bands.