Voltage control oscillator which suppresses phase noise caused by internal noise of the oscillator

A frequency synthesizer in which a generated frequency signal is controlled by an externally provided numerical figure, comprising:

• a Q-bit binary numerical integration circuit that integrates a given numerical value K provided from the outside in the form of a Q-bit binary coded number by a Q-bit binary adder and a latch driven by the timing of a highly stable reference oscillator;
• a voltage-controlled oscillator (VCO) that generates an output signal with a frequency controlled by an applied control voltage as a reference frequency,
• a frequency divider that divides the frequency of the output of said VCO to generate a pulse signal output at a frequency proper for subsequent processings;
• a P-bit binary integration circuit that integrates a fixed numerical value L driven by the timing of the pulse signal output of said frequency divider;
• an R-bit binary adder that inputs the most significant R bits of said Q-bit binary integration circuit and of said P-bit binary integration circuit and outputs the difference therebetween;
• a D/A converter that converts a digital coded value of an output of said R-bit binary adder into an analog output voltage;
• and
• a low pass filter that smooths the analog output voltage of said D/A converter and provides the control voltage to the VCO.