Patent ID: 6011818
Filing Date: 2000-01-04
Classification: H03J

Abstract:
An automatic frequency control method, comprising:a first process for comparing an oscillation frequency of a voltage controlled oscillator of a phase locked loop with an intermediate frequency, checking an uppermost bit and a lowermost bit of an inner interface control bus, which transmits the comparison result to a control section, increasing and decreasing a frequency value of the voltage controlled oscillator according to the bit check result, and storing the frequency value when the oscillation frequency of the voltage controlled oscillator is synchronized with the intermediate frequency; anda second process for checking whether an oscillation control voltage is in a range for operating the phase locked loop when the frequency of the voltage controlled oscillator is not tuned with the intermediate frequency in the first process, increasing or decreasing the frequency value of the voltage controlled oscillator according to the voltage checking result, and storing the frequency value when the voltage of the voltage controlled oscillator is in a range for operating the phase locked loop; wherein the said second process includes:a first step for checking the oscillation control voltage of the voltage controlled oscillator;a second step for decreasing the value of the voltage controlled oscillator when the oscillation control voltage of the voltage controlled oscillator in the first step is larger than a first reference voltage, increasing the value of the voltage controlled oscillator when the oscillation control voltage of the voltage controlled oscillator in the first step is less than a second reference voltage, which is lower than the first reference voltage, incrementing a counter value and determining whether the counter value is larger than a predetermined value.