AUTOMATIC CLOCK SWITCHING CIRCUIT

摘要

PURPOSE: An automatic clock switching circuit is provided to generate a switching control signal and stabilize an operation of a digital system by monitoring digitally a state of a remote clock. CONSTITUTION: An automatic clock switching circuit includes a clock switching portion, a frequency multiplication portion(32), and a clock switching control signal generation portion(30). The clock switching portion outputs selectively a remote clock as a system operating clock and switches a local clock to the system operating clock by selecting the local clock according to an active state of a clock switching signal. The frequency multiplication portion performs a frequency multiplication process for the local clock. The clock control signal generation portion performs a repeated counting operation during a predetermined time by sampling the remote clock and activates the clock switching signal when the counted value is less than the predetermined value.