Patent ID: 7218176

Claim:
A digital phase-locked loop circuit for generating a control voltage signal that is used to enable a voltage controlled oscillator to generate a target frequency output, said digital phase-locked loop circuit comprising: a counter for outputting a count value corresponding to an output frequency outputted by the voltage controlled oscillator in response to the control voltage signal; a comparator coupled to said counter and receiving the count value therefrom, said comparator comparing the count value with a target value associated with the target frequency output and outputting a comparison signal according to a comparison result therebetween; a digital reference value generator coupled to said comparator and receiving the comparison signal therefrom, said digital reference value generator outputting a digital reference value according to the comparison signal, and including a register for storing the digital reference value therein; a digital-to-analog converter coupled to said digital reference value generator and receiving the digital reference value therefrom, said digital-to-analog converter generating the control voltage signal from the digital reference value; a low-pass filter coupled to said digital-to-analog converter for processing the control voltage signal therefrom; and wherein said comparator further outputs a measured difference value that is a difference between the target value and the count value, said digital phase-locked loop circuit further comprising a control circuit coupled to said comparator and said low-pass filter, said control circuit receiving the measured difference value from said comparator, comparing the measured difference value with a standard difference value, and selectively enabling and disabling said low-pass filter according to a comparison result between the measured difference value and the standard difference value.