Patent ID: 7323943

Claim:
A PLL circuit comprising: a phase frequency detector, receiving a reference clock signal and a divided clock signal, for comparing phase or frequency of the reference clock signal with phase or frequency of the divided clock signal to output an up signal or a down signal depending on whether the phase of the divided clock signal leads or lags the phase of the reference clock signal, respectively, or on whether the frequency of the divided clock signal is lower or higher than the frequency of the reference clock signal, respectively; a charge pump circuit, receiving the up and down signals, for causing current to flow out to an output thereof and to flow in from the output thereof, responsive to said up signal and to said down signal, respectively, for outputting an error signal associated with phase or frequency difference detected by said phase frequency detector; a low-pass filter, receiving the error signal, for smoothing the error signal to output a control voltage; a voltage controlled oscillator, receiving the control voltage for generating an output clock signal, the frequency of which is controlled to vary to a higher or lower value in accordance with higher or lower level of said control signal, respectively; a divider circuit, receiving the output clock signal, for dividing the frequency of the output clock signal by a preset frequency division ratio to output said divided clock signal; and a deadlock detection circuit for detecting the falling of the PLL circuit into a deadlock state to output a deadlock detection signal; said deadlock detection circuit including a counter circuit for counting a clock signal, said deadlock detection circuit outputting the deadlock detection signal responsive to a signal output from said counter circuit when said counter circuit has counted a preset number of said clock signal in the deadlock state, said deadlock state being removed by said deadlock detection signal and being detected by monitoring one of said up and down signals.