Abstract: A novel programmable lock detector in phase locked loop is fabricated in SMIC 0.18μm process.A novel pulse width detector in the lock detector is proposed to compare its programmable threshold with the pulse width of the phase detector's output which is proportional to the phase error,and the results are adopted to judge whether PLL is locked.A clock extractor is proposed to get clock from not only the reference clock but also the feedback clock of PLL as the system drive clock,so that the circuit could keep working correctly when the reference clock is lost.The measurements results show that the lock detector works well and can make accurate judgment with different thresholds.