Patent ID: 6859073

Claim:
A frequency synthesizer to lock the frequency controlled oscillator (VCO) with a reference frequency, comprising: a reference frequency; a phase detector; a low pass filter to filter out any ac component from said phase detector and to derive a dc control voltage; and a voltage controlled oscillator (VCO), whose frequency is divided by a divider to compare with said reference frequency and is controlled by said dc control voltage, which is applied in two sequential modes: a calibration mode and an analog mode, wherein said calibration mode locks coarsely said VCO into limited number of discrete frequency steps within a predetermined frequency tolerance of the reference frequency by resetting and holding said dc control voltage in a coarse phase-locked loop, and said analog mode starts with the said dc control voltage reset and held during the calibration mode for fine adjustment of said VCO frequency to lock with said reference frequency in a fine phase-locked loop.