DIGITAL CHARGE PUMP TYPE PLL CIRCUIT

摘要

PURPOSE:To prevent the fluctuation of the follower clock frequency despite the fault of a reference clock. CONSTITUTION:When a reference clock has a fault, a fault detector 8 detects this fault and at the same time forcibly sets the output value of an up-down counter 5 at the digital value equivalent to the center frequency of a VCO 7. This digital value is converted into the analog voltage value by a D/A converter 6 and inputted to the VCO 7. The output frequency of the VCO 7 is fixed at the center frequency.