Frequency synthesizer for use in radio transmitter and receiver

Claim 2

A frequency synthesizer comprising: reference oscillator means for generating a reference oscillation signal; phase comparing means for generating a phase error signal concerning said reference oscillation signal and a frequency-divided signal; a loop filter operative on the basis of said phase error signal for generating and outputting a control voltage; voltage-controlled oscillator means for generating an oscillation signal of a frequency responsive to said control voltage; frequency-multiplying means for sending out a frequency-multiplied signal which is a frequency-multiplied version of said oscillation signal; frequency-dividing means for frequency-dividing said frequency-multiplied signal to supply said frequency-divided signal to said phase comprising means; and a band pass filter for letting a predetermined frequency band of said frequency-multiplied signal pass as an output of the frequency synthesizer.

Claim 3

The frequency synthesizer as defined in claim 1 wherein said frequency multiplying means comprises: an input resonance circuit which resonates said oscillation signal from said voltage-controlled oscillator means; and an amplifying and frequency-multiplying circuit for amplifying and frequency-multiplying a resonated oscillation signal from said input resonance circuit, said amplifying and frequency-multiplying circuit including: an output resonance circuit which resonates said frequency-multiplied signal.

Claim 4

The frequency synthesizer as defined in claim 2 wherein: said amplifying and frequency-multiplying circuit comprises a transistor.

Claim 5

The frequency synthesizer as defined in claim 2, wherein said amplifying and frequency-multiplying circuit comprises: a semiconductor device for distorting said resonated oscillation signal from said input resonance circuit.

Claim 6

The frequency synthesizer as defined in claim 4 wherein: said semiconductor device comprises a variable-capacitance diode.

Claim 7

The frequency synthesizer as defined in claim 1 wherein: said frequency dividing means is so arranged as to down convert said frequency of said oscillation signal from said voltage-controlled oscillator means into one of a plurality of frequencies with constant spacing.

Claim 8

The frequency synthesizer as defined in claim 6 wherein: said frequency dividing means is provided with setting means for setting said frequency of said oscillation signal for a desired one of said plurality of frequencies.

Claim 9

The frequency synthesizer as defined in claim 2, wherein: said output resonance circuit comprises a series resonance circuit; said output resonance circuit comprises a parallel resonance circuit; and said input and said output resonance circuit each comprises an inductor and a capacitor.

Claim 10

The frequency synthesizer as defined in claim 8 wherein: said capacitor comprises a distributed capacitance in the circuit.

Claim 11

A radio communication apparatus having an antenna for receiving a radio signal, a frequency synthesizer for generating a local oscillation signal, demodulating means for demodulating said radio signal with said local oscillation signal and outputting a demodulated signal, and outputting means for outputting said demodulated signal, wherein said frequency synthesizer comprises: reference oscillating means for supplying a reference oscillation signal; phase comparator means for outputting a phase error signal between said reference oscillation signal and a frequency-divided signal; a loop filter for producing a control voltage on the basis of said phase error signal; voltage-controlled oscillator means for sending out an oscillation signal with a frequency responsive to said control voltage; frequency multiplying means for frequency-multiplying said oscillation signal to send out said frequency-multiplied oscillation signal as said local oscillation signal; frequency dividing means for frequency-dividing said frequency-multiplied oscillation signal and supplying said frequency-divided signal to said phase comparator means; and a band pass filter for letting a predetermined frequency band of said frequency-multiplied signal pass as said local oscillation signal.

Claim 12

A radio communication apparatus having an antenna for receiving a radio signal, a frequency synthesizer for generating a local oscillation signal, demodulating means for demodulating said radio signal with said local oscillation signal and outputting a demodulated signal, and outputting means for outputting said demodulated signal, wherein said frequency synthesizer comprises: reference oscillating means for supplying a reference oscillation signal; phase comparator means for outputting a phase error signal between said reference oscillation signal and a frequency-divided signal; a loop filter for producing a control voltage on the basis of said phase error signal; voltage-controlled oscillator means for sending out an oscillation signal with a frequency responsive to said control voltage; frequency multiplying means for frequency-multiplying said oscillation signal to send out said frequency-multiplied oscillation signal as said local oscillation signal; frequency dividing means for frequency-dividing said frequency-multiplied oscillation signal and supplying said frequency-divided signal to said phase comparator means; and a band pass filter for letting a predetermined frequency band of said frequency-multiplied signal pass as said local oscillation signal.