Wide lock range phase locked loop type frequency synthesizer capable of enhancing precision of phase/frequency comparator without increasing lockup time and its method for selecting oscillation frequency

A phase locked loop type frequency synthesizer comprising:

• a phase/frequency comparator for receiving an input signal;
• a charge pump circuit connected to said phase/frequency comparator;
• a bias voltage source for generating a bias voltage;
• a loop filter, selectively connected to one of said charge pump circuit and said bias voltage, for generating a control voltage, said charge pump circuit charging and discharging said loop filter in accordance with an output signal of said phase/frequency comparator, said bias voltage source applying said bias voltage to said loop filter;
• a voltage control oscillator block connected to said loop filter and including a plurality of voltage controlled oscillators controlled by said control voltage;
• a first frequency divider connected to said voltage controlled oscillator block;
• a second frequency divider connected to said first frequency divider, said phase/frequency comparator comparing a phase of said input signal with a phase of an output signal of said second frequency divider;
• a selecting circuit, connected to said first frequency divider and said voltage controlled oscillator block, for selecting and activating only one of said voltage controlled oscillators;
• said selecting circuit counting a number of output pulses of said first frequency divider within a predetermined number of output pulses of said input signal while applying said bias voltage to said loop filter, the one of said voltage controlled oscillators being selected so that;
• the number of the output pulses of said first frequency divider is brought close to an optimum value.