| 摘要 |
PROBLEM TO BE SOLVED: To provide a phase synchronous circuit capable of performing automatic adjustment so that a VCO (voltage-controlled circuit) can meet a prescribed frequency range even within a frequency range that the VCO oscillates due to a leak current caused when a low threshold process is applied. SOLUTION: This phase synchronous circuit is composed of a PLL part comprising a phase comparator 1, a charge pump 2, a loop filter 3, the VCO 4, and a frequency divider 5, and a calibration circuit 14 for automatically adjust a frequency range of the VCO. A switch SW1 is closed with a signal Rst of the calibration circuit 14 before convergence start, and a loop filter output is grounded to make the loop open. A VCO output Fo is set to an upper limit or lower limit frequency with a Vcal signal, the cycle of the Vcal signal is compared with the cycle of a reference signal Fr to measure a frequency, and signals Hb and Lb for adjusting the frequency of the VCO are updated. The signals Hb and Lb are updated until the VCO satisfies the prescribed frequency range, a value is subsequently held, the SW1 is opened with the Rst signal, and the PLL is switched to a closed loop to start phase synchronization. |
